Conditional Weighted Residuals (CWRES): A Model Diagnostic for the FOCE Method

Population pharmacokinetic modeling of zavegepant, a calcitonin gene-related peptide receptor antagonist, in healthy adults and patients with migraine

Zavegepant (ZAVZPRET™) is a high-affinity, selective, small-molecule calcitonin gene-related peptide receptor antagonist available for acute treatment of migraine in adults. A population pharmacokinetic analysis was performed to describe zavegepant plasma concentration-time course, characterize bioavailability, and identify covariates affecting zavegepant exposure. The model was developed and validated using data from 10 phase I clinical studies, wherein zavegepant was administered intravenously, intranasally, or orally to healthy adults and patients with migraine. Plasma concentration-time data were analyzed using nonlinear mixed-effects modeling. A three-compartment model with first-order elimination from the central compartment, and sequential zero- and first-order absorption best described the observed plasma concentration-time course of zavegepant. Bioavailability was 5.1% and 0.65% for intranasal and oral treatment, respectively; absorption rate constants were 5.8 and 0.8 h-1, respectively. Body weight-based empirical allometric scaling was applied using standard exponents (0.75 for clearance and 1 for volume of distribution). Age (range 18-71 years), race, ethnicity, sex, renal function, and co-administration of oral contraceptives or sumatriptan did not significantly change zavegepant pharmacokinetics. Moderate hepatic impairment (Child-Pugh score 7-9) or co-administration of rifampin decreased elimination clearance of oral zavegepant by ~40%. The zavegepant population pharmacokinetic model adequately characterized zavegepant concentration-time profiles, the bioavailability of intranasal and oral zavegepant, as well as the effect of intrinsic and extrinsic factors on zavegepant pharmacokinetics.

Exposure-Response Analysis of Tofacitinib in Active Psoriatic Arthritis: Results from Two Phase 3 Studies

Tofacitinib is an oral Janus kinase inhibitor for the treatment of psoriatic arthritis (PsA). These post hoc exposure-response (E-R) analyses of pooled data from two Phase 3 studies (NCT01877668 and NCT01882439) characterized the relationships between tofacitinib exposure and efficacy (American College of Rheumatology [ACR] criteria), and changes in hemoglobin (Hgb) in patients with PsA. Efficacy data for the proportion of patients receiving tofacitinib 5 or 10 mg twice daily, or placebo, achieving ACR ≥20%, ≥50%, or ≥70% response criteria (ACR20, ACR50, and ACR70, respectively) at Month 3, were modeled jointly using a four-category ordered categorical exposure-response model (ACR20 non-responder, ACR20 responder but not ACR50 responder, ACR50 responder but not ACR70 responder, and ACR70 responder). A maximum drug effect (Emax) model (using average concentrations of tofacitinib at steady state [Cavg]) adequately described the exposure-ACR response rate relationship. Model-predicted response rates for tofacitinib 5 and 10 mg twice daily were 51% and 58%, respectively, for ACR20; 29% and 36% for ACR50; and 15% and 20% for ACR70. The E-R relationship between tofacitinib exposure and changes in Hgb was assessed using an indirect response model, which generally predicted Hgb concentration-time profiles across treatments well. The proportions of patients experiencing a decrease in Hgb of >2 g/dL were similar with tofacitinib 5 mg twice daily or placebo. These results were generally consistent with previous analyses in rheumatoid arthritis and psoriasis, and support the use of tofacitinib 5 mg twice daily for active PsA.

A fully automatic tool for development of population pharmacokinetic models

Population pharmacokinetic (PK) models are widely used to inform drug development by pharmaceutical companies and facilitate drug evaluation by regulatory agencies. Developing a population PK model is a multi-step, challenging, and time-consuming process involving iterative manual model fitting and evaluation. A tool for fully automatic model development (AMD) of common population PK models is presented here. The AMD tool is implemented in Pharmpy, a versatile open-source library for pharmacometrics. It consists of different modules responsible for developing the different components of population PK models, including the structural model, the inter-individual variability (IIV) model, the inter-occasional variability (IOV) model, the residual unexplained variability (RUV) model, the covariate model, and the allometry model. The AMD tool was evaluated using 10 real PK datasets involving the structural, IIV, and RUV modules in three sequences. The different sequences yielded generally consistent structural models; however, there were variations in the results of the IIV and RUV models. The final models of the AMD tool showed lower Bayesian Information Criterion (BIC) values and similar visual predictive check plots compared with the available published models, indicating reasonable quality, in addition to reasonable run time. A similar conclusion was also drawn in a simulation study. The developed AMD tool serves as a promising tool for fast and fully automatic population PK model building with the potential to facilitate the use of modeling and simulation in drug development.

Optimal dosing regimen of caspofungin in adolescents with allogeneic haematopoietic stem cell transplantation

OBJECTIVES

The optimal dosing regimen of caspofungin in adolescents undergoing allogeneic haematopoietic stem cell transplantation against Candida spp. is unknown. The study aimed to compare body surface area (BSA)-based and fixed dosing regimens through population pharmacokinetic (PPK) analysis and to optimize dosing regimens likely to achieve therapeutic exposures.

METHODS

Opportunistic sampling was used to collect plasma concentrations through a prospective observational pharmacokinetic study. PPK analysis and Monte Carlo simulations (n = 1000) were performed using NONMEM.

RESULTS

A total of 86 samples of 30 adolescents (12-17 years old) were best described by a two-compartment pharmacokinetic model. BSA is the only covariate on clearance and central volume of distribution. For Candida glabrata and Candida albicans, a standard dosing regimen could achieve at least a 90% probability of target attainment for the indicator of AUC0-24/MIC90. Dosing regimen simulations identified a BSA cut-off value of 1.3 m2, where a fixed loading dose (LD) is preferred when BSA ≥ 1.3 m2 and a BSA-based LD is preferred when BSA < 1.3 m2. For maintenance dose (MD), however, the BSA-based dose was proposed, regardless of BSA. The current maximum dosing regimen of LD 70 mg/day and MD 70 mg/day could not result in sufficient antifungal exposure for Candida parapsilosis with MIC90 of 1 mg/L. Furthermore, an LD of 70 mg/day and MD of 60 mg/m2/day rendered 90.4% steady-state trough concentration (Ctrough) over 1 mg/L in the virtual population.

CONCLUSIONS

Our study proposed optimized dosing regimens of caspofungin based on AUC0-24/MIC90 or Ctrough, which may support further individualized treatment.

Trilaciclib dosage in Chinese patients with extensive-stage small cell lung cancer: a pooled pharmacometrics analysis

This study aimed to analyze potential ethnic disparities in the dose-exposure-response relationships of trilaciclib, a first-in-class intravenous cyclin-dependent kinase 4/6 inhibitor for treating chemotherapy-induced myelosuppression in patients with extensive-stage small cell lung cancer (ES-SCLC). This investigation focused on characterizing these relationships in both Chinese and non-Chinese patients to further refine the dosing regimen for trilaciclib in Chinese patients with ES-SCLC. Population pharmacokinetic (PopPK) and exposure-response (E-R) analyses were conducted using pooled data from four randomized phase 2/3 trials involving Chinese and non-Chinese patients with ES-SCLC. PopPK analysis revealed that trilaciclib clearance in Chinese patients was approximately 17% higher than that in non-Chinese patients with ES-SCLC. Sex and body surface area influenced trilaciclib pharmacokinetics in both populations but did not exert a significant clinical impact. E-R analysis demonstrated that trilaciclib exposure increased with a dosage escalation from 200 to 280 mg/m2, without notable changes in myeloprotective or antitumor efficacy. However, the incidence of infusion site reactions, headaches, and phlebitis/thrombophlebitis rose with increasing trilaciclib exposure in both Chinese and non-Chinese patients with ES-SCLC. These findings suggest no substantial ethnic disparities in the dose-exposure-response relationship between Chinese and non-Chinese patients. They support the adoption of a 240-mg/m2 intravenous 3-day or 5-day dosing regimen for trilaciclib in Chinese patients with ES-SCLC.

Population pharmacokinetics of total and unbound valemetostat and platelet dynamics in healthy volunteers and patients with non-Hodgkin lymphoma

Valemetostat is an EZH2/1 inhibitor that has been approved in Japan for the treatment of patients with relapsed/refractory adult T-cell leukemia/lymphoma, based mainly on results from a single-arm phase II trial. It is currently under investigation worldwide for the treatment of other non-Hodgkin lymphomas (NHLs), including peripheral T-cell lymphoma, and for solid tumors. Semi-mechanistic population pharmacokinetic modeling of total and unbound valemetostat and an analysis of the platelet time course during treatment with valemetostat were conducted using data from five clinical trials (two in patients with NHL and three in healthy volunteers). Pharmacokinetic data, including 3162 total/1871 unbound valemetostat observations from 102 patients and 72 healthy volunteers, were described by a three-compartment model with sequential zero-/first-order absorption and saturable binding in the central compartment. Alpha-1-acid glycoprotein (AAG) was the most influential covariate for total valemetostat exposure, yet had little impact on unbound exposure, meaning no dose adjustment was warranted based on AAG levels. The longitudinal platelet data from 101 patients (2313 observations) were adequately described by a modified Friberg model with two proliferation compartments, which characterized unique spontaneous recovery of platelet counts without dose modifications. A model-based simulation quantitatively assessed the proposed dose-adjustment guidance in case of platelet count decreased by comparing the probability of treatment discontinuation due to platelet count decreased with or without the dose adjustment. In summary, the models described observed total and unbound valemetostat concentrations and a unique time course of platelets during treatment, which can justify the clinical dose and provide dose-adjustment guidance.

High adsorption capacity of hemoperfusion on imipenem in critically ill patients with septic shock: a case report

BACKGROUND

Sepsis is a life-threatening organ dysfunction caused by an excessive host response to infection, manifested by elevated levels of inflammatory cytokines. At present, the use of hemoperfusion to remove inflammatory cytokines from the bloodstream has been expanding. Meanwhile, the pharmacokinetics and pharmacodynamics characteristics of antibiotics in critically ill patients may be impacted by hemoperfusion.

CASE PRESENTATION

The patient was a 69-year-old male with poorly controlled type 2 diabetes. When admitted to the ICU, Multiple Organ Dysfunction Syndrome (MODS) appeared within 48 h, and he was suspected of septic shock due to acute granulocytopenia and significantly increased procalcitonin. Broad-spectrum antibiotics imipenem was administered according to Sepsis 3.0 bundle and hemoperfusion lasting 4 h with a neutron-macroporous resin device (HA-380, Jafron, China) five times was conducted to lower the extremely high value of serum inflammatory factors. Blood samples were collected to measure imipenem plasma concentration to investigate the effect of hemoperfusion quantitatively. This study showed that 4 h of hemoperfusion had a good adsorption ability on inflammatory factors and could remove about 75.2% of imipenem.

CONCLUSIONS

This case demonstrated the high adsorption capacity of hemoperfusion on imipenem in critically ill patients. It implies a timely imipenem supplement is required, especially before hemoperfusion.

A Pooled Population Pharmacokinetic Study of Oral and Intravenous Administration of Clavulanic Acid in Neonates and Infants: Targeting Effective Beta-Lactamase Inhibition

Data published on the oral clavulanic acid pharmacokinetics in the pediatric population is lacking. This research aimed to describe clavulanic acid disposition following oral and intravenous administration and to provide insights into clavulanic acid exposure based on threshold concentrations for (pre-)term neonates and infants. This pooled population pharmacokinetic study combined four datasets for analysis in NONMEM v7.4.3. Clavulanic acid exposure was simulated using the percentage of time above the threshold concentrations (%fT > CT). Multiple dosage regimens and amoxicillin/clavulanic acid dosage ratios were evaluated. The cohort consisted of 89 (42 oral, 47 intravenous) subjects (403 samples) with a median (range) postnatal age 54.5 days (0-365), gestational age 37.4 weeks (23.0-41.7), and current bodyweight 3.9 kg (0.6-9.0). A one-compartment model with first-order absorption best described clavulanic acid pharmacokinetics with postnatal age as a covariate on the inter-individual variability of clearance. Oral bioavailability was 24.4% in neonates up to 10 days of age. An oral dosing regimen 90 mg/kg/day amoxicillin/clavulanic acid (4:1 ratio) resulted in 40.2% of simulated patients achieving 100% fT > CT,2mg/L. An amoxicillin/clavulanic acid ratio of 4:1 is preferred for neonatal oral regimens due to the higher exposure along the entire %fT > CT range (0-100%) as ratios higher than 4:1 might result in inadequate exposure. Our results highlight substantial exposure differences (%fT > CT) when using threshold concentrations of 1 mg/L vs. 2 mg/L. This first population pharmacokinetic model for clavulanic acid in neonates may serve as a foundational step for future research, once more precise clavulanic acid targets become available.

A Slow-Exchange Interstitial Fluid Compartment in Volunteers and Anesthetized Patients: Kinetic Analysis and Physiology

BACKGROUND

Physiological studies suggest that the interstitial space contains 2 fluid compartments, but no analysis has been performed to quantify their sizes and turnover rates.

METHODS

Retrospective data were retrieved from 270 experiments where Ringer's solution of between 238 and 2750 mL (mean, 1487 mL) had been administered by intravenous infusion to awake and anesthetized humans (mean age 39 years, 47% females). Urinary excretion and hemoglobin-derived plasma dilution served as input variables in a volume kinetic analysis using mixed-models software.

RESULTS

The kinetic analysis successfully separated 2 interstitial fluid compartments. One equilibrated rapidly with the plasma and the other equilibrated slowly. General anesthesia doubled the rate constants for fluid entering these 2 compartments (from 0.072 to 0.155 and from 0.026 to 0.080 min -1 , respectively). The return flows to the plasma were impeded by intensive fluid therapy; the rate constant for the fast-exchange compartment decreased from 0.251 to 0.050 when the infusion time increased from 15 to 60 minutes, and the rate constant for the slow-exchange compartment decreased from 0.019 to 0.005 when the infused volume increased from 500 to 1500 mL. The slow-exchange compartment became disproportionately expanded when larger fluid volumes were infused and even attained an unphysiologically large size when general anesthesia was added, suggesting that the flow of fluid was restrained and not solely determined by hydrostatic and oncotic forces. The dependence of the slow-exchange compartment on general anesthesia, crystalloid infusion rate, and infusion volume all suggest a causal physiological process.

CONCLUSIONS

Kinetic analysis supported that Ringer's solution distributes in 2 interstitial compartments with different turnover times. The slow compartment became dominant when large amounts of fluid were infused and during general anesthesia. These findings may explain why fluid accumulates in peripheral tissues during surgery and why infused fluid can remain in the body for several days after general anesthesia.

Understanding adefovir pharmacokinetics as a component of a transporter phenotyping cocktail

PURPOSE

Adefovir (as dipivoxil) was selected as a probe drug in a previous transporter cocktail phenotyping study to assess renal organic anion transporter 1 (OAT1), with renal clearance (CLR) as the primary parameter describing renal elimination. An approximately 20% higher systemic exposure of adefovir was observed when combined with other cocktail components (metformin, sitagliptin, pitavastatin, and digoxin) compared to sole administration. The present evaluation applied a population pharmacokinetic (popPK) modeling approach to describe adefovir pharmacokinetics as a cocktail component in more detail.

METHODS

Data from 24 healthy subjects were reanalyzed. After establishing a base model, covariate effects, including the impact of co-administered drugs, were assessed using forward inclusion then backward elimination.

RESULTS

A one-compartment model with first-order absorption (including lag time) and a combination of nonlinear renal and linear nonrenal elimination best described the data. A significantly higher apparent bioavailability (73.6% vs. 59.0%) and a lower apparent absorption rate constant (2.29 h-1 vs. 5.18 h-1) were identified in the combined period compared to the sole administration period, while no difference was seen in renal elimination. The population estimate for the Michaelis-Menten constant (Km) of the nonlinear renal elimination was 170 nmol/L, exceeding the observed range of adefovir plasma maximum concentration, while the maximum rate (Vmax) of nonlinear renal elimination was 2.40 µmol/h at the median absolute estimated glomerular filtration rate of 105 mL/min.

CONCLUSION

The popPK modeling approach indicated that the co-administration primarily affected the apparent absorption and/or prodrug conversion of adefovir dipivoxil, resulting in the minor drug-drug interaction observed for adefovir as a victim. However, renal elimination remained unaffected. The high Km value suggests that assessing renal OAT1 activity by CLR has no relevant misspecification error with the cocktail doses used.

Modeling an evaluation of the efficacy of the novel neuroanalgesic drug mirogabalin for diabetic peripheral neuropathic pain and postherpetic neuralgia therapy

Diabetic peripheral neuropathic pain (DPNP) and postherpetic neuralgia (PHN) are challenging and often intractable complex medical conditions, with a substantial impact on the quality of life. Mirogabalin, a novel voltage-gated Ca2+ channel α2δ ligand, was approved for the indication of DPNP and PHN. However, the time course of effects has not yet been clarified.We aimed to establish pharmacodynamic and placebo effect models of mirogabalin and pregabalin in DPNP and PHN, and to quantitatively compare the efficacy characteristics (maximum efficacy, onset time, and other pharmacodynamic parameters) and safety of mirogabalin and pregabalin. Public databases were comprehensively searched for randomized placebo-controlled clinical trials. A model-based meta-analysis (MBMA) was developed to describe the time course of drug efficacy and placebo effects. Adverse events were compared using a fixed-effects meta-analysis. Sixteen studies including 5,147 participants were eligible for this study. The placebo effect was relatively high and gradually increased with time, and it required at least eight weeks to reach a plateau. The pharmacodynamic model revealed that the maximum pure efficacy for mirogabalin and pregabalin was approximately -7.85 % and -8.86 %, respectively; the efficacy of mirogabalin to relieve DPNP and PHN was not superior to that of pregabalin, and both drugs had similar safety. While the rate constant of the onset rate of pregabalin was approximately thrice as high as that of mirogabalin. In addition, the baseline level of pain was an important factor affecting pregabalin efficacy. These findings are helpful in evaluating the clinical extension value of mirogabalin. They suggest that the high placebo effect and the baseline level of pain should be considered when grouping patients in future research and development of voltage-gated Ca2+ channel neuroanalgesic.

Population Pharmacokinetics of Cabozantinib in Metastatic Renal Cell Carcinoma Patients: Towards Drug Expenses Saving Regimens

INTRODUCTION

Cabozantinib is one of the preferred treatment options in the latest metastatic renal cell carcinoma (mRCC) guidelines. Cabozantinib is also associated with high drug expenses irrespective of the used dose, because a flat-prizing model has been implemented. In addition, concomitant intake with a high-fat meal increases its bioavailability on average by 57%. Combined with the long terminal half-life of cabozantinib (99 h), this creates possibilities to extend the dosing interval to reduce drug expenses whilst maintaining equivalent exposure.

OBJECTIVES

The primary objective was to evaluate the population pharmacokinetic (POPPK) model of cabozantinib developed for its registration using real-world patients' therapeutic drug monitoring (TDM) data. The secondary objective was to design, simulate, and evaluate alternative dose regimens with the aim to reduce drug expenses whilst maintaining comparable exposure.

METHODS

Retrospective TDM data from mRCC patients treated with cabozantinib were obtained. The data were evaluated using the published Food and Drug Administration (FDA) cabozantinib POPPK model, a two-compartment disposition model with a dual (fast and slow) lagged first-order absorption process derived from FDA registration documents, as a basis. Subsequently, simulations of alternative drug expenses saving regimens were evaluated.

RESULTS

Twenty-seven mRCC patients with 75 pharmacokinetic observations were included. Patients were treated for a median of 75 days with a median dose of 40 mg. Model evaluation results showed that the cabozantinib TDM concentrations were adequately predicted by the published FDA cabozantinib POPPK model, except for a slightly higher clearance (CL) of 3.11 L/h compared to the reported value (2.23 L/h). The simulation study indicated that an alternative dose regimen that consists of taking 60 mg of cabozantinib for 2 days and then skipping 1 day results in comparable average exposure when compared with a 40 mg daily dose, both without food interaction, while saving 33.3% of the total drug expenses per month. The food effect of a high-fat meal was also taken into account when simulating other alternative dose regimens; 40 mg every 72 h combined with a high-fat meal resulted in comparable exposure when compared with a 20 mg daily dose fasted, while saving 66.7% in drug expenses.

CONCLUSIONS

In this study, the optimized cabozantinib POPPK model resulted in adequate prediction of real-world cabozantinib pharmacokinetic data. Alternative dosing regimens with and without using known food interactions were proposed that resulted in potential strategies to significantly reduce cabozantinib drug expenses.

Integrating Clopidogrel's First-Pass Effect in a Joint Semi-Physiological Population Pharmacokinetic Model of the Drug and Its Inactive Carboxylic Acid Metabolite

Clopidogrel (CLO), a pro-drug for preventing thrombotic events, undergoes rapid absorption and extensive metabolism, with approximately 85-90% converted to an inactive carboxylic acid metabolite (CLO-CA) and the remaining to an active thiol (CLO-TH). Few pharmacokinetic models for the drug and its metabolites exist, with most focusing on CLO-TH. Although CLO-CA is inactive, its predominant (compared to its parent drug and metabolites) presence in plasma underscores the importance of characterizing its formation and pharmacokinetic profile. This study aimed to characterize the process of the absorption of CLO and its conversion to CLO-CA via developing a population pharmacokinetic model. Individual participants' data from two bioequivalence studies were utilized. Extensive blood samples were collected at predetermined intervals, including 841 concentrations of CLO and 1149 of CLO-CA. A nonlinear, mixed-effects modelling approach using NONMEM® software (v 7.5) was applied. A one-compartment model was chosen for CLO, while a two-compartment proved optimal for CLO-CA. Absorption from the depot compartment was modeled via two transit compartments, incorporating transit rate constants (Ktr). A semi-physiological model explained the first-pass effect of CLO, integrating a liver compartment. The estimated mean transit times (MTTs) for the studies were 0.470 and 0.410 h, respectively. The relative bioavailability for each study's generic medicine compared to the reference were 1.08 and 0.960, respectively. Based on the estimated parameters, the fractions metabolized to inactive metabolites (FiaM_st1 and FiaM_st2) were determined to be 87.27% and 86.87% for the two studies, respectively. The appropriateness of the final model was confirmed. Our model offers a robust framework for elucidating the pharmacokinetic profiles of CLO and CLO-CA.

Population pharmacokinetics, dosing optimization and clinical outcomes of biapenem in patients with sepsis

Introduction: Biapenem is a carbapenem antibiotic widely used in Asia, can be used for the treatment of adults and children with infections due to susceptible bacteria. Although biapenem is utilized in the treatment of a diverse range of bacterial infections, current pharmacokinetic data in the context of septic populations remain limited. Consequently, our research aims to evaluate the pharmacokinetics and efficacy of biapenem within a septic population to optimize biapenem therapy. Methods: In this study, we characterized the pharmacokinetics of biapenem in septic patients using a population pharmacokinetic (PPK) approach. The clinical PK data to develop the PPK model were obtained from 317 septic patients admitted to Nanjing Drum Tower Hospital between 2018 and 2022. All patients were randomized to the modeling and validation cohorts at a 3:1 ratio, with PPK modeling and validation performed utilizing the NONMEM software. Results: The model found to best describe the available data was a two-compartment PPK model with first-order elimination characterized by the parameters clearance (CL), central volume (V1), peripheral volume (V2), and intercompartmental clearance (Q). A covariate analysis identified that creatinine clearance (CLCR) was a significant covariate influencing biapenem CL, while blood urea nitrogen (BUN) was a significant covariate influencing biapenem Q. Accoding to the clinical outcome analyses, 70% of the time that the free antimicrobial drug concentration exceeds the MIC (fT >MIC) is associated with favourable clinical outcomes. The PPK model was then used to perform Monte Carlo simulations to evaluate the probability of attaining 70% fT >MIC. Conclusions: A final PPK model of biapenem was established for patients with sepsis. The current daily dosage regimen of 1.2 g may insufficient to achieve 70% fT >MIC in septic patients. The dosage regimen of 600 mg every 6 h appears to be the optimal choice.

Understanding hemoglobin contribution to high-dose methotrexate disposition-population pharmacokinetics in pediatric patients with hematological malignancies

PURPOSE

The aim of the present study was to develop a population pharmacokinetic model for methotrexate (MTX) during high-dose treatment (HDMTX) in pediatric patients with acute lymphoblastic leukemia (ALL) and non-Hodgkin's lymphoma (NHL) and to describe the influence of variability factors.

METHODS

The study included 50 patients of both sexes (aged 1-18 years) who received 3 or 5 g/m2 of HDMTX. A nonlinear mixed effect modeling approach was applied for data analysis. Parameter estimation was performed by first-order conditional estimation method with interaction (FOCEI), whereas stepwise covariate modeling was used to assess variability factors.

RESULTS

The final model is a two-compartment model that incorporates the effect of body surface area and the influence of hemoglobin and serum creatinine on MTX clearance (CL). Population pharmacokinetic values for a typical subject were estimated at 5.75 L/h/m2 for clearance (CL), 21.3 L/m2 for volume of the central compartment (V1), 8.2 L/m2 for volume of the peripheral compartment (V2), and 0.087 L/h/m2 for intercompartmental clearance (Q). According to the final model, MTX CL decreases with increasing serum creatinine, whereas a positive effect was captured for hemoglobin. A difference of almost 32% in MTX CL was observed among patients' hemoglobin values reported in the study.

CONCLUSION

The developed population pharmacokinetic model can contribute to the therapy optimization during HDMTX in pediatric patients with ALL and NHL. In addition to renal function and body weight, it describes the influence of hemoglobin on CL, allowing better understanding of its contribution to the disposition of HDMTX.

CYP2D6 Phenotype Influences Pharmacokinetic Parameters of Venlafaxine: Results from a Population Pharmacokinetic Model in Older Adults with Depression

In this study, we aimed to improve upon a published population pharmacokinetic (PK) model for venlafaxine (VEN) in the treatment of depression in older adults, then investigate whether CYP2D6 metabolizer status affected model-estimated PK parameters of VEN and its active metabolite O-desmethylvenlafaxine. The model included 325 participants from a clinical trial in which older adults with depression were treated with open-label VEN (maximum 300 mg/day) for 12 weeks and plasma levels of VEN and O-desmethylvenlafaxine were assessed at weeks 4 and 12. We fitted a nonlinear mixed-effect PK model using NONMEM to estimate PK parameters for VEN and O-desmethylvenlafaxine adjusted for CYP2D6 metabolizer status and age. At both lower doses (up to 150 mg/day) and higher doses (up to 300 mg/day), CYP2D6 metabolizers impacted PK model-estimated VEN clearance, VEN exposure, and active moiety (VEN + O-desmethylvenlafaxine) exposure. Specifically, compared with CYP2D6 normal metabolizers, (i) CYP2D6 ultra-rapid metabolizers had higher VEN clearance; (ii) CYP2D6 intermediate metabolizers had lower VEN clearance; (iii) CYP2D6 poor metabolizers had lower VEN clearance, higher VEN exposure, and higher active moiety exposure. Overall, our study showed that including a pharmacogenetic factor in a population PK model could increase model fit, and this improved model demonstrated how CYP2D6 metabolizer status affected VEN-related PK parameters, highlighting the importance of genetic factors in personalized medicine.

Population Pharmacokinetics of Ozoralizumab in Patients with Rheumatoid Arthritis

Ozoralizumab is a bispecific NANOBODY compound that binds tumor necrosis factor alpha (TNFα) and human serum albumin. Ozoralizumab inhibits the TNFα physiological activity while maintaining long-term plasma retention owing to its human serum albumin-binding ability. A population pharmacokinetic (PK) model was developed using data from 494 Japanese patients with rheumatoid arthritis in Phase II/III and Phase III trials to assess the effects of potential PK covariates. The ozoralizumab PK after subcutaneous administration was described using a 1-compartment model with first-order absorption and first-order elimination processes. A proportional error model was used for inter- and intra-individual variabilities, with covariance set between inter-individual variabilities of the apparent clearance and apparent distribution volume. Body weight, sex, antidrug antibody status, estimated glomerular filtration rate, and concomitant methotrexate use were identified as covariates for apparent clearance, while body weight and sex were covariates for apparent distribution volume in the final model. Body weight had the greatest effect on the PK of ozoralizumab, while the other covariates had minor effects. When administered at 30 mg every 4 weeks, the predicted steady-state plasma trough concentration in a patient weighing 83.2 kg exceeded the trough concentration required to maintain efficacy of ozoralizumab, and the estimated exposure in a patient weighing 42.5 kg did not exceed the mean exposure at 80 mg, a well-tolerated dose, throughout 52 weeks. We developed a population PK model that adequately described the ozoralizumab PK in Japanese patients with rheumatoid arthritis, and none of the evaluated covariates showed clinically relevant effects on the PK of ozoralizumab.

Accelerating drug development for amyotrophic lateral sclerosis: construction and application of a disease course model using historical placebo group data

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is an irreversible degenerative disease. Placebo-controlled randomized trials are currently the main trial design to assess the clinical efficacy of drugs for ALS treatment. The aim of this study was to establish models to quantitatively describe the course of ALS, explore influencing factors, and provide the necessary information for ALS drug development.

METHODS

We conducted a comprehensive search of PubMed and the Cochrane Library Central Register for placebo-controlled trials that evaluated treatments for ALS. From these trials, we extracted the clinical and demographic characteristics of participants in the placebo group, as well as outcome data, which encompassed overall survival (OS) and Amyotrophic Lateral Sclerosis Functional Rating Scale (ALSFRS-R) scores, at various time points.

RESULTS

In total, 47 studies involving 6118 participants were included. Disease duration and the proportion of patients receiving riluzole were identified as significant factors influencing OS in the placebo group. Specifically, the median OS was 35.5 months for a disease duration of 9 months, whereas it was 20.0 months for a disease duration of 36 months. Furthermore, for every 10% increase in the proportion of patients treated with riluzole (100 mg daily), there was an association with a median OS extension of approximately 0.4 months. The estimated time for the ALSFRS-R score in the placebo group to decrease to 50% of its maximum effect from baseline level was approximately 17.5 months, and the time to reach a plateau was about 40 months.

CONCLUSIONS

The established disease course model of the historical placebo group is valuable in the decision-making process for the clinical development of ALS drugs. It serves not only as an external control to evaluate the efficacy of the tested drug in single-arm trials but also as prior information that aids in accurately estimating the posterior distribution of the disease course in the placebo group during small-sample clinical trials.

Evidence of serial connection between the plasma volume and two interstitial fluid compartments

BACKGROUND

Kinetic analysis of fluid volume shifts can identify two interstitial fluid compartments with different turnover rates, but how they are connected to the bloodstream is unknown.

METHODS

Retrospective data were retrieved from 217 experiments where 1.5 L of Ringer's solution (mean) had been administered by intravenous infusion over 30 min to awake and anesthetized humans (mean age 40 years). Urinary excretion and hemoglobin-derived plasma dilution served as input variables in a volume kinetic analysis using mixed models software. Possible modes of connection between the two interstitial fluid compartments and the bloodstream were judged by covariance analysis between kinetic rate constants, physiological variables, and time factors.

RESULTS

The return flow of already distributed fluid to the plasma via a fast-exchange interstitial compartment was inhibited ongoing infusion of fluid (-38 %), which was probably due to increase of the venous pressure during volume loading. Ongoing infusion also greatly retarded the entrance of fluid to the slow-exchange compartment (-85 %), which suggests that infused Ringer's first had to enter the fast-exchange compartment. A high mean arterial pressure markedly increased the urine output and, to a lesser degree, also the rate of entrance of fluid to the fast-exchange compartment. Moreover, a high blood hemoglobin concentration retarded the rate of entrance of fluid to the fast-exchange compartment.

CONCLUSIONS

The fast-exchange but not the slow-exchange interstitial fluid compartment was affected by intravascular events, which suggests that only the fast-exchange compartment is directly connected to the circulating blood.

A Physiologically Based Pharmacokinetic Approach to Recommend an Individual Dose of Tacrolimus in Adult Heart Transplant Recipients

Tacrolimus is the principal immunosuppressive drug which is administered after heart transplantation. Managing tacrolimus therapy is challenging due to a narrow therapeutic index and wide pharmacokinetic (PK) variability. We aimed to establish a physiologically based pharmacokinetic (PBPK) model of tacrolimus in adult heart transplant recipients to optimize dose regimens in clinical practice. A 15-compartment full-PBPK model (Simbiology® Simulator, version 5.8.2) was developed using clinical observations from 115 heart transplant recipients. This study detected 20 genotypes associated with tacrolimus metabolism. CYP3A5*3 (rs776746), CYP3A4*18B (rs2242480), and IL-10 G-1082A (rs1800896) were identified as significant genetic covariates in tacrolimus pharmacokinetics. The PBPK model was evaluated using goodness-of-fit (GOF) and external evaluation. The predicted peak blood concentration (Cmax) and area under the drug concentration-time curve (AUC) were all within a two-fold value of the observations (fold error of 0.68-1.22 for Cmax and 0.72-1.16 for AUC). The patients with the CYP3A5*3/*3 genotype had a 1.60-fold increase in predicted AUC compared to the patients with the CYP3A5*1 allele, and the ratio of the AUC with voriconazole to alone was 5.80 when using the PBPK model. Based on the simulation results, the tacrolimus dosing regimen after heart transplantation was optimized. This is the first PBPK model used to predict the PK of tacrolimus in adult heart transplant recipients, and it can serve as a starting point for research on immunosuppressive drug therapy in heart transplant patients.

Evaluation of postprandial total triglycerides within the TIGG model for characterizing postprandial response of glucose, insulin, and GLP-1

The TIGG model is the first model to integrate glucose and insulin regulation, incretin effect, and triglyceride (TG) response in the lipoprotein subclasses of chylomicrons and VLDL-V6. This model described the response following a high-fat meal in individuals who are lean, obese, and very obese and provided insights into the possible regulation of glucose homeostasis in the extended period following a meal. Often, total TGs are analyzed within clinical studies, instead of lipoprotein subclasses. We extended the existing TIGG model to capture the observed total TGs and determined if this model could be used to predict the postprandial TG response of chylomicron and VLDL-V6 when only total TGs are available. To assess if the lipoprotein distinction was important for the model, a second model (tTIGG) was developed using only the postprandial response in total TGs, instead of postprandial TG response in chylomicrons and VLDL-V6. The two models were compared on their predictability to characterize the postprandial response of glucose, insulin, and active GLP-1. Both models were able to characterize the postprandial TG response in individuals who are lean, obese, or very obese following a high-fat meal. The extended TIGG model resulted in a better model fit of the glucose data compared to the tTIGG model, indicating that chylomicron and VLDL-V6 provided additional information compared to total TGs. Furthermore, the expanded TIGG model was able to predict the postprandial TG response of chylomicrons and VLDL-V6 using the total TGs and could therefore be used in studies where only total TGs were collected.

Population pharmacokinetics of esaxerenone, a novel non-steroidal mineralocorticoid receptor blocker, in patients with essential hypertension, patients with diabetic nephropathy, and healthy volunteers

OBJECTIVES

Esaxerenone is a novel, non-steroidal mineralocorticoid receptor (MR) blocker with improved selectivity and affinity for MR. The objectives of this study were to model the population pharmacokinetics of esaxerenone in a diverse population and to evaluate the effect of covariates on pharmacokinetics parameters.

METHODS

A total of 8263 plasma esaxerenone concentrations from 166 healthy volunteers, 1097 hypertensive patients and 360 patients with diabetic nephropathy were pooled. A three-compartment model with sequential zero- and first-order absorption was used to describe the time-courses of plasma esaxerenone following single and multiple doses once daily for up to 12 weeks. Covariate effects were estimated using the full covariate modeling approach. Clinical relevance of covariates was ascertained using tornado plots.

RESULTS

Esaxerenone was estimated to have high bioavailability (85.3%), low clearance (3.28 L/h) and relatively large distribution volume at steady state (94.8 L). Body weight (-26 to +36%) and coadministration of itraconazole (+64%) or rifampicin (-68%) were associated with a greater influence on esaxerenone exposure.

CONCLUSIONS

The most influential covariates on esaxerenone exposure were coadministrations of itraconazole and rifampicin, followed by body weight. The clinical relevance of effects of renal impairment, mild to moderate hepatic impairment, and age is limited.

Phase I, Randomized, Placebo-Controlled, Dose-Escalation Study of GB223, a Fully-Humanized Monoclonal Antibody to RANKL, in Healthy Chinese Adults

BACKGROUND

GB223 is a novel, fully-humanized monoclonal antibody against the receptor activator of nuclear factor-kappa B ligand (RANKL). In this phase I study, the safety, tolerability, pharmacokinetics, pharmacodynamics, and immunogenicity of GB223 were investigated.

PATIENTS AND METHODS

This was a randomized, double-blinded, placebo-controlled, single-dose escalation study conducted in 44 healthy Chinese adults. Participants were randomly assigned to receive a single subcutaneous injection dose of 7, 21, 63, 119, or 140 mg of GB223 (n = 34) or placebo (n = 10) and were followed up for 140-252 days.

RESULTS

The results of noncompartmental analysis showed that GB223 was slowly absorbed after dosing, with a time to reach maximum concentration (Tmax) ranging from 5 to 11 days. Serum GB223 concentrations decreased slowly, with a long half-life ranging from 7.91 to 19.60 days. A two-compartment Michaelis-Menten model was found to best describe the pharmacokinetics of GB223, and the absorption rate of GB223 differed between males (0.0146 h-1) and females (0.0081 h-1). Serum C-terminal telopeptide of type I collagen decreased significantly postdose, and the inhibition lasted 42-168 days. No deaths or drug-related serious adverse events occurred. The most frequent adverse events were blood parathyroid hormone increased (94.1%), blood phosphorus decreased (67.6%) and blood calcium decreased (58.8%). In the GB223 group, 44.1% (15/34) of subjects were antidrug antibody positive after dosing.

CONCLUSION

In this study, we demonstrated for the first time that a single subcutaneous injection of GB223, from 7 to 140 mg, is safe and well tolerated in healthy Chinese subjects. GB223 has a nonlinear pharmacokinetic profile, and sex was a potential covariate that may affect the absorption rate of GB223.

CLINICAL TRIAL REGISTRATION

NCT04178044 and ChiCTR1800020338.

Optimization of secukinumab dose regimens in patients with moderate-to-severe plaque psoriasis via exposure-response modeling

BACKGROUND

Further dose optimization is required for patients with moderate-to-severe plaque psoriasis who do not benefit from the approved secukinumab dose regimen. This study aimed to develop an exposure-response model for secukinumab to recommend dose regimens for patients of different body weights.

METHODS

We searched the PubMed and Cochrane Library databases for randomized controlled trials using PASI 75 and PASI 90 response rates as primary outcomes. A model-based meta-analysis was developed to quantitatively analyze the distribution of six secukinumab dose regimens in patients weighing 50-120 kg.

RESULTS

Sixteen trials involving 6,197 subjects were included in the analysis. The established model accurately described the time-course characteristics of PASI 75 and PASI 90 response rates over 52 weeks. Simulations indicated that maintenance doses could be reduced to 150 mg every 4 weeks and to 150 mg every 3 weeks for patients weighing 50 and 60 kg, respectively. In contrast, maintenance doses of 300 mg every 3 weeks should be selected for patients weighing 120 kg. Patients weighing 70-110 kg remained on approved maintenance doses of 300 mg every 4 weeks.

CONCLUSIONS

Based on patient body weights, the exposure-response model recommends efficacious and economical dose regimens for patients with moderate-to-severe plaque psoriasis.

Therapeutic Drug Monitoring and Population Pharmacokinetic Analysis of Teicoplanin among Chinese Patients with Gram-Positive Infections in a Tertiary Hospital

Background. To explore the use of teicoplanin among Chinese patients with Gram-positive infections in a tertiary hospital. Methods. The medical records of patients, who were monitored for teicoplanin plasma concentration (TPC) from December 2017 to February 2019, were collected. By combining the therapeutic drug monitoring (TDM) and nonlinear mixed-effects model, a population pharmacokinetic (PPK) model of teicoplanin was established. Results. The proportions of TPCs lower and higher than 10 mg/L were nearly the same (102 vs. 108 cases). A two-compartment model of teicoplanin PPK in Chinese patients was established. Compared with 400 mg, the 600 mg regimen was more able to reach the target concentration (10 mg/L), especially for high-weight patients. Conclusions. The standard regimen of teicoplanin, 400 mg, failed to reach the target value in the present population. Moreover, the 600 mg regimen was feasible for high-weight patients based on TDM and individualized pharmacokinetic dosing adjustment.

Population pharmacokinetics of ruxolitinib in children with hemophagocytic lymphohistiocytosis: focus on the drug-drug interactions

PURPOSE

The optimal dose regimen of ruxolitinib (RUX) in children with hemophagocytic lymphohistiocytosis (HLH) remains to be determined. The aim was to develop and verify a population pharmacokinetic (PPK) model, and then provide references for the optimization of dose regimen of RUX in children with HLH.

METHODS

A total of 189 RUX concentrations from 32 children were included. The PPK model was established using the nonlinear mixed-effects model approach. Predictive performance and stability of the final PPK model were evaluated. The exposure of RUX in different clinical scenarios was simulated through Monte Carlo simulations.

RESULTS

A one-compartment model with first-order absorption and linear elimination was identified to describe the disposition of RUX. The absorption rate constant (K_a) in the final PPK model was 1.05 h^-1, and the apparent clearance (CL/F) and volume of distribution (V/F) were 9.80 L/h and 30.6 L, respectively. Coadministration with triazoles (TZS) and azithromycin (AZM) resulted in approximately 31.0% and 32.4% reductions in the CL/F of RUX, respectively. Multiple evaluation procedures showed satisfactory predictive performance and stability of the final model. Monte Carlo simulations showed that the exposure of RUX was significantly affected by the coadministration with TZS and/or AZM under different clinical scenarios.

CONCLUSION

For the first time, a PPK model of RUX in children with HLH was developed and evaluated. The coadministration with TZS and/or AZM were found to reduce the clearance of RUX in children. These findings could provide new insights for the precise treatment of RUX in children with HLH.

Fractal Kinetic Implementation in Population Pharmacokinetic Modeling

Compartment modeling is a widely accepted technique in the field of pharmacokinetic analysis. However, conventional compartment modeling is performed under a homogeneity assumption that is not a naturally occurring condition. Since the assumption lacks physiological considerations, the respective modeling approach has been questioned, as novel drugs are increasingly characterized by physiological or physical features. Alternative approaches have focused on fractal kinetics, but evaluations of their application are lacking. Thus, in this study, a simulation was performed to identify desirable fractal-kinetics applications in conventional modeling. Visible changes in the profiles were then investigated. Five cases of finalized population models were collected for implementation. For model diagnosis, the objective function value (OFV), Akaike's information criterion (AIC), and corrected Akaike's information criterion (AICc) were used as performance metrics, and the goodness of fit (GOF), visual predictive check (VPC), and normalized prediction distribution error (NPDE) were used as visual diagnostics. In most cases, model performance was enhanced by the fractal rate, as shown in a simulation study. The necessary parameters of the fractal rate in the model varied and were successfully estimated between 0 and 1. GOF, VPC, and NPDE diagnostics show that models with the fractal rate described the data well and were robust. In the simulation study, the fractal absorption process was, therefore, chosen for testing. In the estimation study, the rate application yielded improved performance and good prediction-observation agreement in early sampling points, and did not cause a large shift in the original estimation results. Thus, the fractal rate yielded explainable parameters by setting only the heterogeneity exponent, which reflects true physiological behavior well. This approach can be expected to provide useful insights in pharmacological decision making.

Population pharmacokinetics and limited sampling strategy for therapeutic drug monitoring of mycophenolate mofetil in Japanese patients with lupus nephritis

BACKGROUND

Mycophenolate mofetil (MMF), a prodrug of the immunosuppressive agent mycophenolic acid (MPA), is difficult to administer because of the pharmacokinetic complexity of MPA. Although dosage adjustment according to the 12-h area under the concentration-time curve (AUC0-12) is thought to be desirable, multiple blood samplings for AUC calculation may pose a clinical challenge. A limited sampling strategy (LSS) would provide a solution; however, little is known about MPA pharmacokinetics in lupus nephritis patients, especially in those with Asian backgrounds, or few, if any, LSSs are reported for them.

METHODS

Thirty-four adult Japanese patients receiving MMF for lupus nephritis were examined retrospectively. MPA pharmacokinetics were investigated, and a PPK model was developed using Phoenix® NLME™ software. Single and double blood sampling strategies from Bayesian estimation using the PPK model and from multiple linear regression were compared. Tolerability was also evaluated.

RESULTS

In the pharmacokinetic analysis, renal function and serum albumin had significant effects on dose-normalized AUC0-12; and serum albumin, concomitant proton pump inhibitor (PPI) and iron/magnesium oxide did on dose-normalized maximum concentration. As a PPK model, a two-compartment model was developed with a transit absorption model and first-order elimination, in which creatinine clearance and serum albumin were covariates for MPA clearance. The double sampling strategy at 1 and 4 h by multiple linear regression showed the best agreement with the observed AUC0-12 (r2 = 0.885). Of the single sampling strategies, the one at 6 h by Bayesian estimation performed best (r2 = 0.769). The tolerability evaluation showed that correlations were suggested for gastrointestinal involvement.

CONCLUSIONS

The present study developed the first PPK model of MPA for Japanese lupus nephritis patients. As for LSSs, a double sampling strategy at 1 and 4 h by multiple linear regression would work best; when only a single blood sampling is allowed, a strategy at 6 h by Bayesian estimation using the PPK model developed in this study would be best. The LSSs good enough for clinical use may facilitate safer, more effective, and individualized therapy.

Joint population pharmacokinetic modeling of venlafaxine and O-desmethyl venlafaxine in healthy volunteers and patients to evaluate the impact of morbidity and concomitant medication

Introduction: Venlafaxine (VEN) is a widely used dual selective serotonin/noradrenaline reuptake inhibitor indicated for depression and anxiety. It undergoes first-pass metabolism to its active metabolite, O-desmethyl venlafaxine (ODV). The aim of the present study was to develop a joint population pharmacokinetic (PPK) model to characterize their pharmacokinetic characters simultaneously. Methods: Plasma concentrations with demographic and clinical data were derived from a bioequivalence study in 24 healthy subjects and a naturalistic TDM setting containing 127 psychiatric patients. A parent-metabolite PPK modeling was performed with NONMEM software using a non-linear mixed effect modeling approach. Goodness of fit plots and normalized prediction distribution error method were used for model validation. Results and conclusion: Concentrations of VEN and ODV were well described with a one-compartment model incorporating first-pass metabolism. The first-pass metabolism was modeled as a first-order conversion. The morbid state and concomitant amisulpride were identified as two significant covariates affecting the clearance of VEN and ODV, which may account for some of the variations in exposure. This model may contribute to the precision medication in clinical practice and may inspire other drugs with pre-system metabolism.

Timing of Live Attenuated Vaccination in Infants Exposed to Infliximab or Adalimumab in Utero: A Prospective Cohort Study in 107 Children

BACKGROUND AND AIMS

For infants exposed in utero to anti-tumour necrosis factor-α [TNF] medications, it is advised that live-attenuated vaccinations be postponed until the drug is cleared, but little is known about time to clearance. To minimize delays before live-attenuated vaccination can be given, we aimed to develop a pharmacokinetic model to predict time-to-clearance in infants exposed during pregnancy.

METHODS

We prospectively followed in utero infliximab/adalimumab-exposed infants of mothers with inflammatory bowel disease across four countries between 2011 and 2018. Infants with a detectable anti-TNF umbilical-cord level and at least one other blood sample during the first year of life were included.

RESULTS

Overall, 107 infants were enrolled, including 166 blood samples from 71 infliximab-exposed infants and 77 samples from 36 adalimumab-exposed infants. Anti-TNF was detectable in 23% [n = 25] of infants at 6 months. At 12 months, adalimumab was not detected but 4% [n = 3] had detectable infliximab. A Bayesian forecasting method was developed using a one-compartment pharmacokinetic model. Model validation showed that the predicted clearing time was in accordance with the measured observations. A clinician-friendly online calculator was developed for calculating full anti-TNF clearing time: https://xiaozhu.shinyapps.io/antiTNFcalculator2/.

CONCLUSIONS

Almost one-quarter of infants born to mothers receiving anti-TNF during pregnancy have detectable anti-TNF at 6 months. To limit the time to live-attenuated vaccination in infants of mothers receiving anti-TNF during pregnancy, the results of a cord drug level at birth and a second sample ≥ 1 month thereafter can be used to estimate the time for full anti-TNF clearance in these children.

Population Pharmacokinetics of Oral Brepocitinib in Healthy Volunteers and Patients

Brepocitinib is a tyrosine kinase 2 and Janus kinase 1 inhibitor in development for treatment of inflammatory autoimmune diseases. This analysis aimed to add to the pharmacokinetic knowledge of the medication, through development of a population pharmacokinetic model and identification of factors that affect drug disposition. Plasma samples from 5 clinical trials were collated, composed of healthy volunteers, patients with psoriasis and patients with alopecia areata taking oral brepocitinib. NONMEM was used to develop a population pharmacokinetic model, and patient demographics were tested as covariates. The final model was a 1-compartment model with first-order absorption. The typical values for apparent clearance and apparent volume of distribution were 18.7 L/h (78% coefficient of variation [CV]) and 136 L (60.5% CV), respectively. Absorption was rapid with an absorption constant of 3.46 h, with an absorption lag of 0.24 hours observed with the oral tablet formulation. The proportional residual error was found to be 52.7% CV in healthy volunteers and 87.5% CV in patients. High-fat meals were associated with a reduction in both the rate (69.9% lower) and extent (28.3% lower) of absorption, while Asian populations had reduced clearance (24.3% lower). Nonlinear pharmacokinetics were observed at doses of 175 mg and above, with a 35.1% higher relative bioavailability at these doses. There were insufficient data to describe this nonlinearity as a continuous relationship. This initial description of the population pharmacokinetics will act as a foundation for the model-informed drug development of brepocitinib and will facilitate future modeling of this medicine. ClinicalTrials.gov numbers NCT02310750 NCT03236493 NCT03656952 NCT02969018 NCT02974868.

Population Pharmacokinetic/Pharmacodynamic Modelling of Daptomycin for Schedule Optimization in Patients with Renal Impairment

The aims of this study are (i) to develop a population pharmacokinetic/pharmacodynamic model of daptomycin in patients with normal and impaired renal function, and (ii) to establish the optimal dose recommendation of daptomycin in clinical practice. Several structural PK models including linear and non-linear binding kinetics were evaluated. Monte Carlo simulations were conducted with a fixed combination of creatinine clearance (30-90 mL/min/1.73 m2) and body weight (50-100 kg). The final dataset included 46 patients and 157 daptomycin observations. A two-compartment model with first-order peripheral distribution and elimination kinetics assuming non-linear protein-binding kinetics was selected. The bactericidal effect for Gram+ strains with MIC ≤ 0.5 mg/L could be achieved with 5-12 mg/kg daily daptomycin based on body weight and renal function. The administration of 10-17 mg/kg q48 h daptomycin allows to achieve bactericidal effect for Gram+ strains with MIC ≤ 1 mg/L. Four PK samples were selected as the optimal sampling strategy for an accurate AUC estimation. A quantitative framework has served to characterize the non-linear binding kinetics of daptomycin in patients with normal and impaired renal function. The impact of different dosing regimens on the efficacy and safety outcomes of daptomycin treatment based on the unbound exposure of daptomycin and individual patient characteristics has been evaluated.

Population pharmacokinetic modeling of caffeine in preterm infants with apnea of prematurity: New findings from concomitant erythromycin and AHR genetic polymorphisms

Current standard-dose caffeine therapy results in significant intersubject variability. The aims of this study were to develop and evaluate population pharmacokinetic (PPK) models of caffeine in preterm infants through comprehensive screening of covariates and then to propose model-informed precision dosing of caffeine for this population. A total of 129 caffeine concentrations from 96 premature neonates were incorporated into this study. Comprehensive medical record and genotype data of these neonates were collected for analysis. PPK modeling was performed by a nonlinear mixed effects modeling program (NONMEM). Final models based on the current weight (CW) or body surface area (BSA) were evaluated via multiple graphic and statistical methods. The model-informed dosing regimen was performed through Monte Carlo simulations. In addition to CW or BSA, postnatal age, coadministration with erythromycin (ERY), and aryl hydrocarbon receptor coding gene (AHR) variant (rs2158041) were incorporated into the final PPK models. Multiple evaluation results showed satisfactory prediction performance and stability of the CW- and BSA-based models. Monte Carlo simulations demonstrated that trough concentrations of caffeine in preterm infants would be affected by concomitant ERY therapy and rs2158041 under varying dose regimens. For the first time, ERY and rs2158041 were found to be associated with the clearance of caffeine in premature infants. Similar predictive performance and stability were obtained for both CW- and BSA-based PPK models. These findings provide novel insights into caffeine precision therapy for preterm infants.

Pharmacokinetics of Dantrolene in the Plasma Exchange Treatment of Malignant Hyperthermia in a 14-Year-Old Chinese Boy: A Case Report and Literature Review

Malignant hyperthermia (MH) is a rare life-threatening response that is triggered by exposure to specific anesthetics commonly used during surgical interventions. Dantrolene is a well-known drug used as the first-line therapy for MH. A 14-year-old Chinese boy with a mutation in type 1 Ryanodine receptor (RyR1) whose muscle biopsy diagnosis was central core disease (CCD) had an occurrence of MH after a cervical spine surgery, during which he was placed under general anesthesia without volatile anesthetics or succinylcholine. The MH crisis treatment workflow was started and intravenous dantrolene was used, which was soon combined with sequent continuous veno-venous hemofiltration (CVVH) and plasma exchange (PE) therapy. We explored the pharmacokinetic profile of dantrolene during PE treatment. It showed that a one-compartment model with first-order kinetics was sufficient to characterize dantrolene pharmacokinetics (PK). The renal clearance estimate for dantrolene was 0.33 mL/(min*kg) and the volume of distribution was 0.51 L/kg. Though a 4-h PE elevated about 27% off-clearance for dantrolene, it eliminated extra dantrolene by a mere 4% of the area under the curve (AUC). We made no recommendation with respect to adjusting dantrolene dosing for MH adolescents with a 4-h PE.

Kinetics of 5% and 20% albumin: A controlled crossover trial in volunteers

BACKGROUND

Albumin for intravenous infusion is marketed in two concentrations, 20% and 5%, but how they compare with regard to plasma volume expansion over time is unclear.

METHODS

In a prospective crossover study, 12 volunteers received 3 ml kg-1 of 20% albumin and, on another occasion, 12 ml kg-1 of 5% albumin over 30 min. Hence, equivalent amounts of albumin were given. Blood was collected on 15 occasions over 6 h. Mass balance and volume kinetics were used to estimate the plasma volume expansion and the capillary leakage of albumin and fluid based on measurements of blood hemoglobin, plasma albumin, and the colloid osmotic pressure.

RESULTS

The greatest plasma volume expansion was 16.0 ± 6.4% (mean ± SD) with 20% albumin and 19.0 ± 5.2% with 5% albumin (p < .03). The volume expansion with 20% albumin corresponded to twice the infused volume. One third of the 5% albumin volume quickly leaked out of the plasma, probably because of the higher colloid osmotic pressure of the volunteer plasma (mean, 24.5 mmHg) than the albumin solution (19.1 mmHg). At 6 h, the capillary leakage amounted to 42 ± 15% and 47 ± 11% of the administered albumin with the 20% and 5% preparations, respectively (p = .28). The corresponding urine outputs were 547 (316-780) ml and 687 (626-1080) ml (median and interquartile range; p = .24).

CONCLUSION

The most important difference between the fluids was a dehydrating effect of 20% albumin when the same albumin mass was administered.

Impact of Obesity on Postprandial Triglyceride Contribution to Glucose Homeostasis, Assessed with a Semimechanistic Model

The integrated glucose-insulin model is a semimechanistic model describing glucose and insulin after a glucose challenge. Similarly, a semiphysiologic model of the postprandial triglyceride (TG) response in chylomicrons and VLDL-V6 was recently published. We have developed the triglyceride-insulin-glucose-GLP-1 (TIGG) model by integrating these models and active GLP-1. The aim was to characterize, using the TIGG model, the postprandial response over 13 hours following a high-fat meal in 3 study populations based on body mass index categories: lean, obese, and very obese. Differential glucose and lipid regulation were observed between the lean population and obese or very obese populations. A population comparison revealed further that fasting glucose and insulin were elevated in obese and very obese when compared with lean; and euglycemia was achieved at different times postmeal between the obese and very obese populations. Postprandial insulin was incrementally elevated in the obese and very obese populations compared with lean. Postprandial chylomicrons TGs were similar across populations, whereas the postprandial TGs in VLDL-V6 were increased in the obese and very obese populations compared with lean. Postprandial active GLP-1 was diminished in the very obese population compared with lean or obese. The TIGG model described the response following a high-fat meal in individuals who are lean, obese, and very obese and provided insight into the possible regulation of glucose homeostasis in the extended period after the meal by utilizing lipids. The TIGG-model is the first model to integrate glucose and insulin regulation, incretin effect, and postprandial TGs response in chylomicrons and VLDL-V6.

Population Pharmacokinetics of Antimalarial Naphthoquine in Combination with Artemisinin in Tanzanian Children and Adults: Dose Optimization

The combination antimalarial therapy of artemisinin-naphthoquine (ART-NQ) was developed as a single-dose therapy, aiming to improve adherence relative to the multiday schedules of other artemisinin combination therapies. The pharmacokinetics of ART-NQ has not been well characterized, especially in children. A pharmacokinetic study was conducted in adults and children over 5 years of age (6 to 10, 11 to 17, and ≥18 years of age) with uncomplicated malaria in Tanzania. The median weights for the three age groups were 20, 37.5, and 55 kg, respectively. Twenty-nine patients received single doses of 20 mg/kg of body weight for artemisinin and 8 mg/kg for naphthoquine, and plasma drug concentrations were assessed at 13 time points over 42 days from treatment. We used nonlinear mixed-effects modeling to interpret the data, and allometric scaling was employed to adjust for the effect of body size. The pharmacokinetics of artemisinin was best described by one-compartment model and that of naphthoquine by a two-compartment disposition model. Clearance values for a typical patient (55-kg body weight and 44.3-kg fat-free mass) were estimated as 66.7 L/h (95% confidence interval [CI], 57.3 to 78.5 L/h) for artemisinin and 44.2 L/h (95% CI, 37.9 to 50.6 L/h) for naphthoquine. Nevertheless, we show via simulation that patients weighing ≥70 kg achieve on average a 30% lower day 7 concentration compared to a 48-kg reference patient at the doses tested, suggesting dose increases may be warranted to ensure adequate exposure. (This study has been registered at ClinicalTrials.gov under identifier NCT01930331.).

Population Pharmacokinetics of Intravenous Acyclovir in Oncologic Pediatric Patients

Background: Acyclovir represents the first-line prophylaxis and therapy for herpes virus infections. However, its pharmacokinetics in children exposes them to the risk of ineffective or toxic concentrations. The study was aimed at investigating the population pharmacokinetics (POP/PK) of intravenous (IV) acyclovir in oncologic children.

Methods: Patients (age, 8.6 ± 5.0 years, 73 males and 47 females) received IV acyclovir for prophylaxis (n = 94) and therapy (n = 26) under a therapeutic drug monitoring (i.e., minimum and maximal plasma concentrations, >0.5 and <25 mg/L, respectively). Plasma concentrations were fitted by nonlinear mixed effect modeling and a simulation of dosing regimens was performed. Findings were stratified according to an estimated glomerular filtration rate (eGFR) threshold of 250 ml/min/1.73 m².

Results: The final 1-compartment POP/PK model showed that eGFR had a significant effect on drug clearance, while allometric body weight influenced both clearance and volume of distribution. The population clearance (14.0 ± 5.5 L/h) was consistent across occasions. Simulation of standard 1-h IV infusion showed that a 10-mg/kg dose every 6 h achieved target concentrations in children with normal eGFR (i.e., ≤250 ml/min/1.73 m²). Increased eGFR values required higher doses that led to an augmented risk of toxic peak concentrations. On the contrary, simulated prolonged (i.e., 2 and 3-h) or continuous IV infusions at lower doses increased the probability of target attainment while reducing the risk of toxicities.

Conclusion: Due to the variable pharmacokinetics of acyclovir, standard dosing regimens may not be effective in some patients. Prospective trials should confirm the therapeutic advantage of prolonged and continuous IV infusions

Fluconazole Population Pharmacokinetics after Fosfluconazole Administration and Dosing Optimization in Extremely Low-Birth-Weight Infants

A prospective single-center study was conducted to characterize the pharmacokinetics (PK) of fluconazole (FLCZ) in extremely low-birth-weight infants (ELBWIs) who received fosfluconazole (F-FLCZ). Intravenous F-FLCZ was administered at a dose of 3 mg/kg of body weight every 72 h during the first 2 weeks of life, every 48 h during the third and fourth weeks of life, and every 24 h after 5 weeks of life. Blood samples from ELBWIs treated with F-FLCZ were collected using scavenged samples. The concentration of FLCZ was determined using liquid chromatography-tandem mass spectrometry. The population pharmacokinetic model was established using Phenix NLME 8.2 software. In total, 18 ELBWIs were included in this analysis. Individual PK parameters were determined by a one-compartment analysis with first-order conversion. Postmenstrual age (PMA), serum creatinine (SCr), and alkaline phosphatase were considered covariates for clearance (CL). The mean population CL and the volume of distribution were 0.011 L/h/kg^0.75 and 0.95 L/kg, respectively. Simulation assessments with the final model revealed that the current regimen (3 mg/kg every 72 h) could achieve the proposed target FLCZ trough concentration (>2 μg/mL) in 43.3% and 72.2% of infants with a PMA of ≥37 and 30 to 36 weeks, respectively, and an SCr level of <0.5 mg/dL. Shortened dosing intervals (every 48 or 24 h) might improve the probability of target attainment. This study was the first to assess the PK of F-FLCZ in ELBWI, as well as the first to provide fundamental information about FLCZ exposure after F-FLCZ administration, with the goal of facilitating dose optimization in the ELBWI population.

IMPORTANCE Invasive fungal infection is an important cause of mortality and morbidity in very preterm or very-low-birth-weight infants. In order to limit the risk of invasive fungal infections in this population, the administration of fluconazole is generally recommended for extremely low-birth-weight infants admitted to a neonatal intensive care unit with a Candida species colonization prevalence rate of >10%, under the guidelines of the Infectious Diseases Society of America. Fosfluconazole can reduce the volume of solution required for intravenous therapy compared to fluconazole because it has increased solubility, which is a major advantage for infants undergoing strict fluid management. To date, no study has demonstrated the fluconazole pharmacokinetics after fosfluconazole administration in neonates and infants, and this needs to be clarified. Here, we characterized the pharmacokinetics of fluconazole in extremely low-birth-weight infants who received F-FLCZ and explored the appropriate dosage in this patient population.

Quantitative evaluation of drug efficacy in the treatment of myasthenia gravis

OBJECTIVES

This study aimed to quantitatively evaluate placebo effect and drug efficacy characteristics and identify associated factors that affect quantitative myasthenia gravis (MG) score (QMGs) and MG activities of daily living score (MG-ADLs) in patients with MG.

METHODS

Randomized placebo-controlled clinical trials were comprehensively searched in public databases (PubMed, EMBASE, and Cochrane Library databases).A model-based meta-analysis was developed to describe time-course about drug efficacy and placebo effect.

RESULTS

Twelve articles including 13 trials (673 participants) that were eligible for this study evaluated four immunosuppressants (tacrolimus, cyclosporine, prednisone, and mycophenolate mofetil) and five targeted therapy drugs (eculizumab, belimumab, zilucoplan, efgartigimod, and iscalimab). The pharmacodynamic model showed that eculizumab had the highest efficacy in reducing QMGs scores (3.66 points), and efgartigimod had the highest efficacy in reducing MG-ADLs scores (1.97 points). The placebo effect of QMGs and MG-ADLs increased apparently with time and reached 52% and 90% of their maximum effect in 12 weeks, respectively. In addition, this study found that the activities of daily living ability increased with the increase of the proportion of patients undergoing thymectomy.

CONCLUSION

This study analyzed the efficacy characteristics of nine drugs. The present findings provide necessary quantitative information for drug development of MG.

Effects of Letermovir and/or Methylprednisolone Coadministration on Voriconazole Pharmacokinetics in Hematopoietic Stem Cell Transplantation: A Population Pharmacokinetic Study

Objective

The aim of this study was to identify factors affecting blood concentrations of voriconazole following letermovir coadministration using population pharmacokinetic (PPK) analysis in allogeneic hematopoietic stem cell transplant (allo-HSCT) recipients.

Methods

The following data were retrospectively collected: voriconazole trough levels, patient characteristics, concomitant drugs, and laboratory information. PPK analysis was performed with NONMEM^® version 7.4.3, using the first-order conditional estimation method with interaction. We collected data on plasma voriconazole steady-state trough concentrations at 216 timepoints for 47 patients. A nonlinear pharmacokinetic model with the Michaelis–Menten equation was applied to describe the relationship between steady-state trough concentration and daily maintenance dose of voriconazole. After stepwise covariate modeling, the final model was evaluated using a goodness-of-fit plot, case deletion diagnostics, and bootstrap methods.

Results

The maximum elimination rate (V_max) of voriconazole in patients coadministered letermovir and methylprednisolone was 1.72 and 1.30 times larger than that in patients not coadministered these drugs, respectively, resulting in decreased voriconazole trough concentrations. The developed PPK model adequately described the voriconazole trough concentration profiles in allo-HSCT recipients. Simulations clearly showed that increased daily doses of voriconazole were required to achieve an optimal trough voriconazole concentration (1–5 mg/L) when patients received voriconazole with letermovir and/or methylprednisolone.

Conclusions

The development of individualized dose adjustment is critical to achieve optimal voriconazole concentration, especially among allo-HSCT recipients receiving concomitant letermovir and/or methylprednisolone.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40268-021-00365-0.

Pharmacokinetics and Target Attainment of SQ109 in Plasma and Human-Like Tuberculosis Lesions in Rabbits

SQ109 is a novel well-tolerated drug candidate in clinical development for the treatment of drug-resistant tuberculosis (TB). It is the only inhibitor of the MmpL3 mycolic acid transporter in clinical development. No SQ109-resistant mutant has been directly isolated thus far in vitro, in mice, or in patients, which is tentatively attributed to its multiple targets. It is considered a potential replacement for poorly tolerated components of multidrug-resistant TB regimens. To prioritize SQ109-containing combinations with the best potential for cure and treatment shortening, one must understand its contribution against different bacterial populations in pulmonary lesions. Here, we have characterized the pharmacokinetics of SQ109 in the rabbit model of active TB and its penetration at the sites of disease—lung tissue, cellular and necrotic lesions, and caseum. A two-compartment model with first-order absorption and elimination described the plasma pharmacokinetics. At the human-equivalent dose, parameter estimates fell within the ranges published for preclinical species. Tissue concentrations were modeled using an “effect” compartment, showing high accumulation in lung and cellular lesion areas with penetration coefficients in excess of 1,000 and lower passive diffusion in caseum after 7 daily doses. These results, together with the hydrophobic nature and high nonspecific caseum binding of SQ109, suggest that multiweek dosing would be required to reach steady state in caseum and poorly vascularized compartments, similar to bedaquiline. Linking lesion pharmacokinetics to SQ109 potency in assays against replicating, nonreplicating, and intracellular M. tuberculosis showed SQ109 concentrations markedly above pharmacokinetic-pharmacodynamic targets in lung and cellular lesions throughout the dosing interval.

Population Pharmacokinetics and Safety of Dasatinib in Chinese Children with Core-Binding Factor Acute Myeloid Leukemia

BACKGROUND

Dasatinib, an orally administered Src-family kinase inhibitor, is combined with the standard chemotherapeutic regimen to enhance antineoplastic activity against core-binding factor acute myeloid leukemia (CBF-AML) in adults; however, limited data are available for use in children. In the present study, we studied the pharmacokinetics and safety of dasatinib in children.

METHODS

Dasatinib (60 or 80 mg/m² once daily) was administered to 20 children with CBF-AML. Blood samples were collected and drug concentrations were quantified by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Population pharmacokinetic analysis and Monte-Carlo simulations were performed using NONMEM software, and safety analyses were assessed according to the National Cancer Institute Common Terminology Criteria for Adverse Events (NCI-CTCAE) version 4.0 (NCT03844360).

RESULTS

Twenty pediatric patients (3.3-14.4 years of age) were included, and a total of 40 dasatinib concentrations were available for population pharmacokinetic analysis. The mean (standard deviation) of the estimated area under the concentration-time curve extrapolated to steady state (AUC_ss) of dasatinib 60 and 80 mg/m² was 366.1 (146.6) ng·h/mL and 425.3 (150.7) ng·h/mL, respectively. The majority of adverse events were grade 1/2 in severity, including thrombocytopenia, rash, and pain in the extremities. The estimated cumulative incidence of complete remission and complete molecular response were 95.0% and 75.5%, respectively.

CONCLUSIONS

The population pharmacokinetics of orally administered dasatinib were evaluated in pediatric CBF-AML patients. The AUC_ss of dasatinib (80 mg/m²) in CBF-AML pediatric patients was similar to those of dasatinib (100 mg) in adult patients. Dasatinib is well-tolerated in pediatric patients with CBF-AML.

Developmental population pharmacokinetics-pharmacodynamics and dosing optimization of cefoperazone in children

OBJECTIVES

To evaluate the population pharmacokinetics of cefoperazone in children and establish an evidence-based dosing regimen using a developmental pharmacokinetic-pharmacodynamic approach in order to optimize cefoperazone treatment.

METHODS

A model-based, open-label, opportunistic-sampling pharmacokinetic study was conducted in China. Blood samples from 99 cefoperazone-treated children were collected and quantified by HPLC/MS. NONMEM software was used for population pharmacokinetic-pharmacodynamic analysis. This study was registered at ClinicalTrials.gov (NCT03113344).

RESULTS

A two-compartment model with first-order elimination agreed well with the experimental data. Covariate analysis showed that current body weight had a significant effect on the pharmacokinetics of cefoperazone. Monte Carlo simulation showed that for bacteria for which cefoperazone has an MIC of 0.5 mg/L, 78.1% of hypothetical children treated with '40 mg/kg/day, q8h, IV drip 3 h' would reach the pharmacodynamic target. For bacteria for which cefoperazone has an MIC of 8 mg/L, 88.4% of hypothetical children treated with 80 mg/kg/day (continuous infusion) would reach the treatment goal. A 160 mg/kg/day (continuous infusion) regimen can cover bacteria for which cefoperazone has an MIC of 16 mg/L. Nevertheless, even if using the maximum reported dose of 160 mg/kg/day (continuous infusion), the ratio of hypothetical children reaching the treatment target was only 9.9% for bacteria for which cefoperazone has an MIC of 32 mg/L.

CONCLUSIONS

For cefoperazone, population pharmacokinetics were evaluated in children and an appropriate dosing regimen was developed based on developmental pharmacokinetics-pharmacodynamics. The dose indicated in the instructions (20-160 mg/kg/day) can basically cover the clinically common bacteria for which cefoperazone has an MIC of ≤16 mg/L. However, for bacteria for which the MIC is >16 mg/L, cefoperazone is not a preferred choice.

Population pharmacokinetics and biodistribution of benznidazole in mice

OBJECTIVES

To evaluate the population pharmacokinetics of different benznidazole treatment regimens and the drug's biodistribution in mice.

METHODS

Two hundred mice were divided into five groups according to benznidazole dosing regimens: (1) 100 mg/kg/day for 20 days; (2) 100 mg/kg/day for 40 days; (3) 200 mg/kg/day for 20 days; (4) 40 mg/kg/day for 20 days; or (5) 40 mg/kg/day for 40 days. The mice were euthanized and blood, heart, liver, colon and brain were collected. Samples were prepared by liquid-liquid extraction and analysed by HPLC-diode-array detection. The pharmacokinetic analysis of benznidazole was evaluated via non-linear mixed-effects modelling using the NONMEN program.

RESULTS

Our results demonstrate that mouse weight allometrically influences benznidazole clearance; the AUC curve and the highest plasma concentration are dose proportional; benznidazole does not influence its own metabolism; its tissue distribution is limited; and the standard treatment regimen for Chagas' disease in mice (100 mg/kg/day for 20 days) is inadequate from a pharmacokinetic standpoint, as are the other regimens tested in this study (100 mg/kg/day for 40 days, 200 mg/kg/day for 20 days and 40 mg/kg/day for 20 or 40 days).

CONCLUSIONS

Benznidazole reformulations that allow better tissue penetration and plasma and tissue exposure should be evaluated to enable higher cure rates in both animals and patients. The population pharmacokinetic model developed here can allow optimization of the dosing regimen of benznidazole to treat experimental Chagas' disease. Determining appropriate treatment regimens in animals allows translation of these to clinical studies.

Pharmacokinetics of Ruxolitinib in HIV Suppressed Individuals on Antiretroviral Agent Therapy from the ACTG A5336 Study

Ruxolitinib is a US Food and Drug Administration-approved orally administered Janus kinase (1/2) inhibitor that reduces cytokine-induced inflammation. As part of a randomized, phase 2, open-label trial, ruxolitinib (10 mg twice daily) was administered to HIV-positive, virologically suppressed individuals (33 men, 7 women) on antiretroviral therapy (ART) for 5 weeks. Herein, we report the population PK subsequently determined from this study. Plasma concentrations of ruxolitinib (294 samples) and antiretroviral agents were measured at week 1 (N = 39 participants) and week 4 or 5 (N = 37). Ruxolitinib PK was adequately described with a 2-compartment model with first-order absorption and elimination with distribution volumes normalized to mean body weight (91.5 kg) and a separate typical clearance for participants administered efavirenz (a known cytochrome P450 3A4 inducer). Participants administered an ART regimen with efavirenz had an elevated typical apparent oral clearance versus the integrase inhibitor regimen group (22.5 vs 12.9 L/hr; N = 14 vs 25). Post hoc predicted apparent oral clearance was likewise more variable and higher (P < .0001) in those administered efavirenz. There was  an ≈25% variation in ruxolitinib plasma exposures between week 1 and week 4/5. ART plasma concentrations resembled those from PK studies without ruxolitinib. Therefore, integrase inhibitor-based ART regimens may be preferred over efavirenz-based regimens when ruxolitinib is administered to HIV-positive individuals.

A Semimechanistic Pharmacokinetic Model for Depot Medroxyprogesterone Acetate and Drug-Drug Interactions With Antiretroviral and Antituberculosis Treatment

Depot medroxyprogesterone acetate is an injectable hormonal contraceptive, widely used by women of childbearing potential living with HIV and/or tuberculosis. As medroxyprogesterone acetate is a cytochrome P450 (CYP3A4) substrate, drug-drug interactions (DDIs) with antiretroviral or antituberculosis treatment may lead to subtherapeutic medroxyprogesterone acetate concentrations (< 0.1 ng/mL), resulting in contraception failure, when depot medroxyprogesterone is dosed at 12-week intervals. A pooled population pharmacokinetic analysis with 744 plasma medroxyprogesterone acetate concentrations from 138 women treated with depot medroxyprogesterone and antiretroviral/antituberculosis treatment across three clinical trials was performed. Monte Carlo simulations were performed to predict the percentage of participants with subtherapeutic medroxyprogesterone acetate concentrations and to derive alternative dosing strategies. Medroxyprogesterone acetate clearance increased by 24.7% with efavirenz coadministration. Efavirenz plus antituberculosis treatment (rifampicin + isoniazid) increased clearance by 52.4%. Conversely, lopinavir/ritonavir and nelfinavir decreased clearance (28.7% and 15.8%, respectively), but lopinavir/ritonavir also accelerated medroxyprogesterone acetate's appearance into the systemic circulation, thus shortening the terminal half-life. A higher risk of subtherapeutic medroxyprogesterone acetate concentrations at Week 12 was predicted on a typical 60-kg woman on efavirenz (4.99%) and efavirenz with antituberculosis treatment (6.08%) when compared with medroxyprogesterone acetate alone (2.91%). This risk increased in women with higher body weight. Simulations show that re-dosing every 8 to 10 weeks circumvents the risk of subtherapeutic medroxyprogesterone acetate exposure associated with these DDIs. Dosing depot medroxyprogesterone every 8 to 10 weeks should eliminate the risk of subtherapeutic medroxyprogesterone acetate exposure caused by coadministered efavirenz and/or antituberculosis treatment, thus reducing the risk of contraceptive failure.

In vivo pharmacokinetic evaluation of carprofen delivery from intra-articular nanoparticles in rabbits: A population modelling approach

Osteoarthritis is treated with COX or fosfolipase A2 inhibitors such as carprofen, a propionic acid NSAID. The enhancement of its action over the articular cartilage is mandatory to facilitate its therapeutic application. Drug uptake into the cartilage requires high synovial fluid concentrations, anticipating its rapid distribution towards bloodstream. Thus, intraarticular administration improves local targeting of the drug, lining with the site of action. A pharmacokinetic study in rabbits has been performed to evaluate carprofen nanoparticles after intraarticular administration. Pharmacokinetic analysis of plasma profiles through a modelling approach, has demonstrated the rapid distribution of drug outside of synovial chamber but mainly remaining in plasma. The data modelling has demonstrated the existence of two release-absorption processes when the nanoparticles are administered in the synovial space. Additionally, results are predictive of the PK profile of some other species such as cat, dogs or humans.