Pharmacokinetic strategies in deciphering atypical drug absorption profiles

Simultaneous determination of multiple components in rat plasma by UPLC-MS/MS for pharmacokinetic studies after oral administration of Pogostemon cablin extract

Introduction: Pogostemon cablin (PC) is used in traditional Chinese medicine and food, as it exerts pharmacological effects, such as immune-modulatory, antibacterial, antioxidant, antitumor, and antiviral. Currently, the pharmacokinetics (PK) studies of PC mainly focus on individual components. However, research on these individual components cannot reflect the actual PK characteristics of PC after administration. Therefore, the simultaneous determination of multiple components in rat plasma using UPLC-MS/MS was used for the pharmacokinetic study after oral administration of PC extract in this study, providing reference value for the clinical application of PC. Methods: In the present study, a reliable and sensitive ultra-high performance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS) method was developed and validated for the simultaneous determination of 15 prototype components (vanillic acid, vitexin, verbascoside, isoacteoside, hyperoside, cosmosiin, apigenin, β-rhamnocitrin, acacetin, ombuin, pogostone, pachypodol, vicenin-2, retusin, and diosmetin-7-O-β-D-glucopyranoside) in rat plasma after oral administration of the PC extract. Plasma samples were prepared via protein precipitation using acetonitrile, and icariin was used as the internal standard (IS). Results: The intra-day and inter-day accuracies ranged from -12.0 to 14.3%, and the precision of the analytes was less than 11.3%. The extraction recovery rate of the analytes ranged from 70.6-104.5%, and the matrix effects ranged from 67.4-104.8%. Stability studies proved that the analytes were stable under the tested conditions, with a relative standard deviation lower than 14.1%. Conclusion: The developed method can be applied to evaluate the PK of 15 prototype components in PC extracts of rats after oral administration using UPLC-MS/MS, providing valuable information for the development and clinical safe, effective, and rational use of PC.

Cannabidiol Bioavailability Is Nonmonotonic with a Long Terminal Elimination Half-Life: A Pharmacokinetic Modeling-Based Analysis

Background: Oral and inhalation-based cannabidiol (CBD) administration has been clinically evaluated for various therapeutic indications, alongside widespread off-label use. However, the long-term exposure kinetics and varied bioavailability have not been fully characterized. Methods: Human CBD plasma concentration-time profiles from six studies evaluating the oral administration of Epidiolex® and three studies evaluating inhalation-based delivery were obtained. A four-compartment pharmacokinetic (PK) model with Weibull-based oral absorption kinetics was employed to describe the long-term PKs of CBD. Furthermore, a Cedergreen-Ritz-Streibig model was applied to evaluate nonmonotonic oral bioavailability. Results: CBD was extensively distributed into tissue compartments with varied kinetics resulting in a long plasma terminal elimination half-life of >134 h in humans. For once-a-day oral dosing, the plasma trough concentrations require >70 days to reach a steady state. The oral bioavailability of CBD for different doses administered in fasted state follows a nonmonotonic pattern with an inverted U-shaped profile. Oral administration of CBD under fed state or subjects with hepatic impairment yields higher oral bioavailability with varied exposure. In contrast, inhalation-based delivery of CBD, while delivering a similar systemic delivered dose compared with oral dosing due to high device losses, bypasses first-pass metabolism and can be efficient. Conclusion: CBD PKs vary across different doses due to nonmonotonic oral bioavailability, and inhalation-based delivery could minimize such variability in humans. The delayed attainment of steady state and prolonged terminal half-life, resulting from differential but extensive tissue distribution, needs to be considered when dosing CBD in the long term. These fundamental findings are critical for establishing dose-exposure relationship for further clinical evaluation of novel CBD-based therapies.

Escitalopram population pharmacokinetics and remedial strategies based on CYP2C19 phenotype

BACKGROUND AND PURPOSE

CYP2C19 is a key factor influencing escitalopram (SCIT) exposure. However, different studies reported various results. This study aims to develop a population pharmacokinetic (popPK) model characterizes the disposition of SCIT in the Chinese population. Based on the popPK model, the study simulates non-adherence scenarios and proposes remedial strategies to facilitate SCIT personalized therapy.

METHODS

Nonlinear mixed-effects modeling using data from two Chinese bioequivalence studies was employed. Monte-Carlo simulation was used to explore non-adherence scenarios and propose remedial strategies based on the proportion of time within the therapeutic window.

RESULTS

Results showed that a one-compartment model with transit absorption and linear elimination described the data well, CYP2C19 phenotypes and weight were identified as significant covariates impacting SCIT exposure. Patients were recommended to take the entire delayed dose immediately if the delay time was no >12 h, followed by the regular regimen at the next scheduled time. When there is one or two doses missed, taking a double dose immediately was recommended to the CYP2C19 intermediate and extensive population, and a 1.5-fold dose was recommended to the CYP2C19 poor metabolizers with the consideration of adverse effects.

LIMITATION

All samples were derived from the homogenized Chinese healthy population for model building, which may pose certain constraints on the ability to identify significant covariates, such as age.

CONCLUSION

The study highlights the importance of considering patient characteristics for personalized medication and offers a unique perspective on utilizing the popPK repository in precision dosing.

Integrating machine learning with pharmacokinetic models: Benefits of scientific machine learning in adding neural networks components to existing PK models

Recently, the use of machine-learning (ML) models for pharmacokinetic (PK) modeling has grown significantly. Although most of the current approaches use ML techniques as black boxes, there are only a few that have proposed interpretable architectures which integrate mechanistic knowledge. In this work, we use as the test case a one-compartment PK model using a scientific machine learning (SciML) framework and consider learning an unknown absorption using neural networks, while simultaneously estimating other parameters of drug distribution and elimination. We generate simulated data with different sampling strategies to show that our model can accurately predict concentrations in extrapolation tasks, including new dosing regimens with different sparsity levels, and produce reliable forecasts even for new patients. By using a scenario of fitting PK data with complex absorption, we demonstrate that including known physiological structure into an SciML model allows us to obtain highly accurate predictions while preserving the interpretability of classical compartmental models.

Population Pharmacokinetics of Levosimendan and its Metabolites in Critically Ill Neonates and Children Supported or Not by Extracorporeal Membrane Oxygenation

BACKGROUND

Levosimendan (LVSMD) is a calcium-sensitizer inotropic and vasodilator agent whose use might have a beneficial effect on the weaning of venoarterial extracorporeal membrane oxygenation (VA-ECMO). In light of LVSMD pharmacological characteristics, we hypothesized that ECMO may induce major pharmacokinetic (PK) modifications for LVSMD and its metabolites.

OBJECTIVE

The aim of this study was to investigate the PK of LVSMD and its metabolites, and to assess the effects of ECMO on PK parameters.

METHODS

We conducted a multicentric, prospective study (NCT03681379). Twenty-seven infusions of LVSMD were performed, allowing for the collection of 255 blood samples. Non-linear mixed-effects modeling software (MONOLIX®) was used to develop a parent-metabolite PK model of LVSMD and its metabolites.

RESULTS

Most patients received a 0.2 µg/kg/min infusion of LVSMD over 24 h. After elimination of non-reliable samples or concentrations below the limit of quantification, 166, 101 and 85 samples were considered for LVSMD, OR-1855 and OR-1896, respectively, of which 81, 53 and 41, respectively, were drawn under ECMO conditions. Parent-metabolite PK modeling revealed that a two-compartment model with first-order elimination best described LVSMD PK. Use of a transit compartment allowed for an explanation of the delayed appearance of circulating OR-1855 and OR-1896, with the latter following a first-order elimination. Patient weight influenced the central volume of distribution and elimination of LVSMD. ECMO support increased the elimination rate of LVSMD by 78%, and ECMO also slowed down the metabolite formation rate by 85% for OR-1855, which in turn is converted to the active metabolite OR-1896, 14% slower than without ECMO. Simulated data revealed that standard dosing may not be appropriate for patients under ECMO, with a decrease in the steady-state concentration of LVSMD and lower exposure to the active metabolite OR-1896.

CONCLUSIONS

ECMO altered PK parameters for LVSMD and its metabolites. An infusion of LVSMD over 48 h, instead of 24 h, with a slightly higher dose may promote synthesis of the active metabolite OR-1896, which is responsible for the long-term efficacy of LVSMD. Further trials evaluating ECMO effects using a PK/pharmacodynamic approach may be of interest.

REGISTRATION

ClinicalTrials.gov identifier number NCT03681379.

The Finite Absorption Time (FAT) concept en route to PBPK modeling and pharmacometrics

The concept of Finite Absorption Time (FAT) for oral drug administration is set to affect pharmacokinetic analyses, Physiologically-based Pharmacokinetics simulations, and Pharmacometrics.

An Integrated Population Pharmacokinetic Analysis for Posaconazole Oral Suspension, Delayed-Release Tablet, and Intravenous Infusion in Healthy Volunteers

BACKGROUND

Posaconazole is widely used for the prophylaxis and treatment of invasive fungal diseases. Because of the limited and variable absorption of the initially available oral suspension, a delayed-release tablet and intravenous formulation were developed.

OBJECTIVE

This study aimed to characterize the pharmacokinetics, including the absolute oral bioavailability, of all posaconazole formulations in healthy volunteers.

METHODS

Data from 182 healthy volunteers with 3898 densely sampled posaconazole concentrations were pooled from eight phase I clinical studies on the three formulations of various single and multiple dosage regimens between 50 and 400 mg. Analysis and simulations were performed using NONMEM 7.5.0. In the covariate analysis, the influence of food (fed vs fasted), nonlinearity, and for the delayed-release tablet, comedication (antacid, ranitidine, esomeprazole, and metoclopramide) were tested.

RESULTS

A two-compartment model with respectively, four and eight absorption transit compartments, best described the profiles of the oral suspension and delayed-release tablet. For the suspension, both a food effect and a dose-dependent nonlinear bioavailability were quantified, resulting in lower bioavailability when fasted or at a higher dose. The typical bioavailability of the suspension at 100 mg and 400 mg was derived to be respectively, 17.1% and 10.1% under fasted conditions and 59.1% and 49.2% under fed conditions. The absolute bioavailability of the delayed-release tablet was 58.8% (95% confidence interval 33.2-80.4) under fasted conditions and approached complete absorption under fed conditions for dosages up to 300 mg. Food intake reduced the absorption rate constant of the suspension by 52.2% (confidence interval 45.2-59.2). The impact of comedication on the absorption of the delayed-release tablet was not statistically significant. Model-based simulations indicate that under fed conditions, the licensed dosages of the three formulations yield a steady-state trough concentration ≥ 0.7 mg/L in over 90% of healthy volunteers. About 35% of healthy volunteers who receive the licensed 300-mg delayed-release tablet under fasted conditions do not achieve this target, while for the suspension this percentage varies between 55 and 85%, depending on the dose.

CONCLUSIONS

For both oral posaconazole formulations, we quantified bioavailability and absorption rate, including food effects, in healthy volunteers. The pharmacokinetic superiority of the delayed-release tablet was demonstrated under both fed and fasted conditions, compared with the oral suspension. The impact of food on the bioavailability of the delayed-release tablet was larger than anticipated, suggesting that administering the delayed-release tablet with food enhances absorption.

Pharmacodynamics and Bactericidal Activity of Combination Regimens in Pulmonary Tuberculosis: Application to Bedaquiline-Pretomanid-Pyrazinamide

A critical barrier to codevelopment of tuberculosis (TB) regimens is a limited ability to identify optimal drug and dose combinations in early-phase clinical testing. While pharmacokinetic-pharmacodynamic (PKPD) target attainment is the primary tool for exposure-response optimization of TB drugs, the PD target is a static index that does not distinguish individual drug contributions to the efficacy of a multidrug combination. A PKPD model of bedaquiline-pretomanid-pyrazinamide (BPaZ) for the treatment of pulmonary TB was developed as part of a dynamic exposure-response approach to regimen development. The model describes a time course relationship between the drug concentrations in plasma and their individual as well as their combined effect on sputum bacillary load assessed by solid culture CFU counts and liquid culture time to positivity (TTP). The model parameters were estimated using data from the phase 2A studies NC-001-(J-M-Pa-Z) and NC-003-(C-J-Pa-Z). The results included a characterization of BPaZ activity as the most and least sensitive to changes in pyrazinamide and bedaquiline exposures, respectively, with antagonistic activity of BPa compensated by synergistic activity of BZ and PaZ. Simulations of the NC-003 study population with once-daily bedaquiline at 200 mg, pretomanid at 200 mg, and pyrazinamide at 1,500 mg showed BPaZ would require 3 months to attain liquid culture negativity in 90% of participants. These results for BPaZ were intended to be an example application with the general approach aimed at entirely novel drug combinations from a growing pipeline of new and repurposed TB drugs.

Convolution-based approach for modeling the paliperidone extended release and Long-Acting Injectable (LAI) PK of once-, and three-monthly products administration and for optimizing the development of new LAI products

The aim of this paper was to develop a convolution-based modeling approach for describing the paliperidone PK resulting from the administration of extended-release once-a-day oral dose, and once- and three monthly long-acting injectable products and to compare the performances of this approach to the traditional modeling strategy. The results of the analyses indicated that the traditional and convolution-based models showed comparable performances in the characterization of the paliperidone PK. However, the convolution-based approach showed several appealing features that justify the choice of this modeling as a preferred tool for modeling Long Acting Injectable (LAI) products and for deploying an effective model-informed drug development process. In particular, the convolution-based modeling can (a) facilitate the development of in vitro/in vivo correlation, (b) be used to identify formulations with optimal in vivo release properties, and (c) be used for optimizing the clinical benefit of a treatment by supporting the implementation of integrated models connecting in vitro and in vivo drug release, in vivo drug release to PK, and PK to PD and biomarker endpoints. A case study was presented to illustrate the benefits and the flexibility of the convolution-based modeling outcomes. The model was used to evaluate the in vivo drug release properties associated with a hypothetical once-a-year administration of a LAI product with the assumption that the expected paliperidone exposure during a 3-year treatment overlays the exposure expected after repeated administrations of a 3-month LAI product.

Total bodyweight and sex both drive pharmacokinetic variability of fluconazole in obese adults

BACKGROUND

Fluconazole is commonly used to treat or prevent fungal infections. It is typically used orally but in critical situations, IV administration is needed. Obesity may influence the pharmacokinetics and therapeutic efficacy of a drug. In this study, we aim to assess the impact of obesity on fluconazole pharmacokinetics given orally or IV to guide dose adjustments for the obese population.

METHODS

We performed a prospective pharmacokinetic study with intensive sampling in obese subjects undergoing bariatric surgery (n = 17, BMI ≥ 35 kg/m2) and non-obese healthy controls (n = 8, 18.5 ≤ BMI < 30.0 kg/m2). Participants received a semi-simultaneous oral dose of 400 mg fluconazole capsules, followed after 2 h by 400 mg IV. Population pharmacokinetic modelling and simulation were performed using NONMEM 7.3.

RESULTS

A total of 421 fluconazole concentrations in 25 participants (total bodyweight 61.0-174 kg) until 48 h after dosing were obtained. An estimated bioavailability of 87.5% was found for both obese and non-obese subjects, with a 95% distribution interval of 43.9%-98.4%. With increasing total bodyweight, both higher CL and Vd were found. Sex also significantly impacted Vd, being 27% larger in male compared with female participants.

CONCLUSIONS

In our population of obese but otherwise healthy individuals, obesity clearly alters the pharmacokinetics of fluconazole, which puts severely obese adults, particularly if male, at risk of suboptimal exposure, for which adjusted doses are proposed.

A rabbit model to study antibiotic penetration at the site of infection for non-tuberculous mycobacterial lung disease: macrolide case study

Nontuberculous mycobacterial pulmonary disease (NTM-PD) is a potentially fatal infectious disease requiring long treatment duration with multiple antibiotics and against which there is no reliable cure. Among the factors that have hampered the development of adequate drug regimens is the lack of an animal model that reproduces the NTM lung pathology required for studying antibiotic penetration and efficacy. Given the documented similarities between tuberculosis and NTM immunopathology in patients, we first determined that the rabbit model of active tuberculosis reproduces key features of human NTM-PD and provides an acceptable surrogate model to study lesion penetration. We focused on clarithromycin, a macrolide and pillar of NTM-PD treatment, and explored the underlying causes of the disconnect between its favorable potency and pharmacokinetics, and inconsistent clinical outcome. To quantify pharmacokinetic-pharmacodynamic target attainment at the site of disease, we developed a translational model describing clarithromycin distribution from plasma to lung lesions, including the spatial quantitation of clarithromycin and azithromycin in mycobacterial lesions of two patients on long-term macrolide therapy. Through clinical simulations, we visualized the coverage of clarithromycin in plasma and four disease compartments, revealing heterogeneous bacteriostatic and bactericidal target attainment depending on the compartment and the corresponding potency against nontuberculous mycobacteria in clinically relevant assays. Overall, clarithromycin's favorable tissue penetration and lack of bactericidal activity indicated that its clinical activity is limited by pharmacodynamic rather than pharmacokinetic factors. Our results pave the way towards the simulation of lesion pharmacokinetic-pharmacodynamic coverage by multi-drug combinations, to enable the prioritization of promising regimens for clinical trials.

Pharmacodynamics and the Bactericidal Activity of Bedaquiline in Pulmonary Tuberculosis

Bedaquiline is a diarylquinoline antimycobacterial drug and a key component of several regimens in clinical development for treatment of tuberculosis (TB), but with ongoing phase 3 trials that include assessment of simplified dosing. A pharmacokinetic-pharmacodynamic model of bedaquiline Mycobacterium tuberculosis killing kinetics in adults with pulmonary TB was developed to inform dose selection of bedaquiline-containing regimens. The model parameters were estimated with data from the 14-day early bactericidal activity (EBA) study TMC207-CL001 conducted in Cape Town, South Africa. The study included 60 adult males and females with drug-susceptible pulmonary TB, who were administered bedaquiline with loading doses on the first two days followed by once daily 100 mg, 200 mg, 300 mg, or 400 mg. The modeling results included expected values (mean±SD) for a maximum drug kill rate constant equal to 0.23±0.03 log₁₀ CFU/mL sputum/day, a half-maximum effect plasma concentration equal to 1.6±0.3 mg/L, and an average time to onset of activity equal to 40±7 h. Model simulations showed once daily 200 mg, 300 mg, and 400 mg (without loading doses) attained 40%, 50%, and 60%, respectively, of an expected maximum 14-day EBA equal to 0.18 log₁₀ CFU/mL/day, or 10 h/day assessed by liquid culture time to positivity (TTP). Additional simulations illustrated efficacy outcomes during eight weeks of treatment with the recommended and alternative dosages. The results demonstrate a general mathematical and statistical approach to analysis of EBA studies with broad application to TB regimen development.

Impact of target-mediated drug disposition on hetrombopag pharmacokinetics and pharmacodynamics in Chinese healthy subjects and patients with chronic idiopathic thrombocytopenic purpura

AIMS

The pharmacokinetics (PK) of hetrombopag were found to be nonlinear across evaluated dose ranges. The aim of this study was to develop a mechanism-based population pharmacokinetic/pharmacodynamic (PopPK/PD) model and to provide a reasonable expected therapeutic dose for a future confirmatory clinical study of hetrombopag.

METHODS

Nonlinear mixed-effects modelling was performed using pooled 2168 hetrombopag concentrations and 1526 platelet counts from 72 healthy subjects and 32 chronic idiopathic thrombocytopenic purpura (ITP) patients from two phase I studies and one phase II study. The final model was evaluated via goodness-of-fit plots, visual predictive check and nonparametric bootstrap. Simulations from the validated PopPK/PD model were used to devise an expected therapeutic dose for later confirmatory clinical study.

RESULTS

The pharmacokinetic data of hetrombopag were well described by a modified target-mediated drug disposition (TMDD) model with dual sequential first-order absorption. Mean parameter estimates (interindividual variability) were CL/F 7.66 L/h (63.5%), V_c /F 30.0 L (77.2%) and K_deg 0.693/h (87.1%). The pharmacodynamic profile was well described by a five-compartment lifespan model with four-transit and one-platelet compartments. Simulation results suggested that chronic ITP patients following 10 mg once-daily hetrombopag would able to achieve an ideal platelet count level (50-200 × 10⁹ /L).

CONCLUSION

TMDD was the primary reason leading to nonlinear PK profile of hetrombopag. Our PK/PD modelling and simulation results support 10 mg once-daily as the recommended therapeutic dose for chronic ITP patients in subsequent confirmatory clinical study of hetrombopag.

Modeling Complex Pharmacokinetics of Long-Acting Injectable Products Using Convolution-Based Models With Nonparametric Input Functions

The interest in the development and the therapeutic use of long-acting injectable (LAI) products for chronic or long-term treatments has grown exponentially. The complexity and the multiphase drug release process represent serious issues for an effective modeling of the PK properties of LAI products. The objective of this article is to show how convolution-based models with piecewise-linear approximation of the nonlinear drug release function can provide an enhanced modeling tool for (1) characterizing the complex PK profiles of LAI formulations with completely different drug release properties, and (2) addressing key questions supporting the optimal development of LAI products by simulating the PK time course resulting from different dosing strategies. Convolution-based modeling and simulation were implemented in NONMEM, and 3 case studies were presented to assess the performances of this new modeling approach using PK data of LAI products developed using different technologies and administered using different routes: microsphere technology and aqueous nanosuspension intramuscularly administered and biodegradable polymer subcutaneously administered. The performance of the convolution-based modeling approach was compared with the performance of conventional parametric models using a reference data set on theophylline. The results of the comparison indicated that the nonparametric input function provided a more accurate description of the data either in terms of global measure of goodness of fit (ie, Akaike information criterion and Bayesian information criterion) or in terms of performance of the fitted model (ie, the percent prediction error on C_{ma x} and AUC_0-t ).

A Population Pharmacokinetic Model of (R)- and (S-) Oxybutynin and Its Active Metabolites After Oral and Intravesical Administration to Healthy Volunteers

Oxybutynin is a racemic anticholinergic drug used for the symptomatic treatment of detrusor overactivity. The formation of active metabolites related to tolerability problems depends on the route of administration. The objective of this evaluation was to develop a pharmacokinetic model for oral/intravesical administration as the basis for simulations with different dosages. Data from a published changeover clinical study with 18 healthy adults receiving a single oral dose of 5 mg immediate-release oxybutynin and single and multiple intravesical doses of 10 mg oxybutynin solution was evaluated. Enantioselective plasma concentrations of oxybutynin and N-desethyloxybutynin (NDO) were used to establish a population pharmacokinetic model using nonlinear mixed-effects modeling with NONMEM 7.4.1. For both enantiomers, the data were described well by a 2-compartment model for oxybutynin with an additional compartment for NDO. Oxybutynin absorption was modeled by transit compartments for oral and first-order absorption for intravesical application. Bioavailability of the more active (R)-enantiomer was 7% for oral and 10%-22% for intravesical administration. In simulations, intravesical doses of 5 to 15 mg (R)-oxybutynin administered 2 to 3 times daily decreased peak-trough fluctuations of NDO to 8% compared with 24% after oral administration. The NDO/oxybutynin ratio was reduced from 17 after oral administration to unity. Chronic intravesical versus oral administration of (R)-oxybutynin generates distinctly lower and less variable concentrations of (R)-NDO. Pharmacokinetic simulations suggest that exposure for 12.5 mg (R)-oxybutynin administered twice daily might not compromise efficacy and tolerability compared with exposure for standard thrice-daily administrations. This assumption needs to be assessed in clinical studies.

UHPLC-MS/MS method for pharmacokinetic and bioavailability determination of five bioactive components in raw and various processed products of Polygala tenuifolia in rat plasma

CONTEXT

Sibiricose A5 (A5), sibiricose A6 (A6), 3,6'-disinapoyl sucrose (DSS), tenuifoliside A (TFSA) and 3,4,5-trimethoxycinnamic acid (TMCA) are the main active components of Polygala tenuifolia Willd. (Polygalaceae) (PT) that are active against Alzheimer's disease.

OBJECTIVE

To compare the pharmacokinetics and bioavailability of five active components in the roots of raw PT (RPT), liquorice-boiled PT (LPT) and honey-stir-baked PT (HPT).

MATERIALS AND METHODS

The median lethal dose (LD₅₀) was evaluated through acute toxicity test. The pharmacokinetics of five components after oral administration of extracts of RPT, LPT, HPT (all equivalent to 1.9 g/kg of RPT extract for one dose) and 0.5% CMC-Na solution (control group) were investigated, respectively, in Sprague-Dawley rats (four groups, n = 6) using UHPLC-MS/MS. In addition, the absolute bioavailability of A5, A6, DSS, TFSA and TMCA after oral administration (7.40, 11.60, 16.00, 50.00 and 3.11 mg/kg, respectively) and intravenous injection (1/10 of the corresponding oral dose) in rats (n = 6) was studied.

RESULTS

The LD₅₀ of RPT, LPT and HPT was 7.79, 14.55 and 15.99 g/kg, respectively. AUC _{0- t} of RPT, LPT and HPT were as follows: A5 (433.18 ± 65.48, 680.40 ± 89.21, 552.02 ± 31.10 ng h/mL), A6 (314.55 ± 62.73, 545.76 ± 123.16, 570.06 ± 178.93 ng h/mL) and DSS (100.30 ± 62.44, 232.00 ± 66.08, 197.58 ± 57.37 ng h/mL). The absolute bioavailability of A5, A6, DSS, TFSA and TMCA was 3.25, 2.95, 2.36, 1.17 and 42.91%, respectively.

DISCUSSION AND CONCLUSIONS

The pharmacokinetic and bioavailability parameters of each compound can facilitate future clinical studies.

Effects of Carbamazepine and Phenytoin on Pharmacokinetics and Pharmacodynamics of Rivaroxaban

Rivaroxaban (RIV) is commonly prescribed with carbamazepine or phenytoin (CBZ/PHT) in post-stroke seizure or post-stroke epilepsy patients. Although adverse events have been reported in several previous studies when they are coadministered, there are no studies of the interactions between these drugs. Therefore, our study was conducted to solve this lack of information. The potential effects of CBZ/PHT were investigated by comparing the pharmacokinetic (PK) and pharmacodynamic (PD) parameters of RIV between the control group (RIV alone) and the test groups (RIV administered with CBZ/PHT) in rats using the noncompartmental analysis (NCA) and the compartmental model approach. The NCA results indicate that AUC_t of RIV decreased by 57.9% or 89.7% and C_max of RIV decreased by 43.3% or 70.0% after administration of CBZ/PHT, respectively. In addition, both CBZ and PHT generally reduced the effects of RIV on the prothrombin times of the blood samples. PK profiles of RIV were most properly described by a two-compartment disposition model with a mixed first- and zero-order absorption kinetics and a first-order elimination kinetics. The compartmental model approach showed that a 211% or 1030% increase in CL/F of RIV and a 33.9% or 43.4% increase in D2 of RIV were observed in the test groups by the effects of CBZ/PHT, respectively. In conclusion, CBZ and PHT significantly reduced RIV exposure and therefore reduced the therapeutic effects of RIV. Consequently, this might result in adverse events due to insufficient RIV concentration to attain its therapeutic effects. Further studies are needed to validate this finding.

Applying Biopharmaceutical Classification System criteria to predict the potential effect of Cremophor® RH 40 on fexofenadine bioavailability at higher doses

Aim: To study the impact of various permeability enhancers on fexofenadine bioavailability. Furthermore, to predict the potential effect of Cremophor^® RH 40 on fexofenadine pharmacokinetics at higher doses using Biopharmaceutical Classification System criteria. Experimental methods: The effect of the dose increase (60-360 mg) on the dissolution and permeability behavior of fexofenadine-Cremophor RH 40 formulations was studied in humans. The Biopharmaceutical Classification System criteria of the drug was determined. Results & conclusion: Cremophor RH 40 improved the dissolution and bioavailability of fexofenadine. The pharmacokinetics increased linearly with the dose increase. Absorption number (A_n) was significantly increased after addition of Cremophor RH 40 in comparison to an unprocessed drug. Similar A_n values were observed throughout the same dose range. The dose number (D₀) values were <1 whereas, all the dissolution number (D_n) values were >1 at the same dose level.

Pharmacokinetic Drug Interactions of an Orally Available TRH Analog (Rovatirelin) With a CYP3A4/5 and P-Glycoprotein Inhibitor (Itraconazole)

The effects of itraconazole on the pharmacokinetics of rovatirelin were investigated in an open-label, single-sequence drug-drug interaction study in 16 healthy subjects. Subjects were administered a single oral dose of rovatirelin (1.6 mg) on day 1 and day 15. From day 8 through 16, subjects received daily oral doses of itraconazole (200 mg/day). Concentrations of rovatirelin and (thiazolylalanyl)methylpyrrolidine (TAMP), the major metabolite of rovatirelin formed by cytochrome P450 (CYP) 3A4/5, were determined in plasma and urine. Pharmacokinetic parameters were used to evaluate the drug-drug interaction potential of rovatirelin as a victim. With coadministration, maximum concentration (C_max ) and area under the concentration-time curve extrapolated to infinity (AUC_inf ) of rovatirelin increased 3.05-fold and 2.82-fold, respectively, and the 90% confidence intervals of the ratios for C_max (2.64-3.52) and AUC_inf (2.47-3.23) did not fall within the 0.8-1.25 boundaries. Urinary excretion of rovatirelin increased at almost the same ratio as the AUC_inf ratio with coadministration; however, renal clearance did not change. C_max , AUC_inf , and urinary excretion of TAMP were decreased by coadministration. Itraconazole has the potential to inhibit drug transport via intestinal P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP); therefore, substrate assessments of rovatirelin for the 2 transporters were evaluated using Caco-2 cell monolayers. In vitro studies showed that rovatirelin is a substrate for P-gp but not for BCRP. The current study shows that itraconazole's effect on rovatirelin pharmacokinetics is mediated through inhibition of CYP3A4/5 and intestinal P-gp.

Population pharmacokinetics of orally administrated bromopride: Focus on the absorption process

Bromopride is a prokinetic and antiemetic drug used to treat nausea and vomiting. Although its prescription is common in Brazil, there is a lack of studies about bromopride pharmacokinetics. Therefore, the aims of this study were to investigate the population pharmacokinetics of bromopride and to evaluate the influence of covariates on its absorption. This study is a retrospective analysis of data collected from bioequivalence studies. The data was modeled using MONOLIX 2018R2. Assuming one-compartment and linear elimination, the absorption phase was evaluated with different structural models. The model of sequential first- and zero-order with combined error and exponential inter-individual variability in all parameters best described the atypical absorption profile of bromopride. Population estimates were first-order absorption rate (ka) of 0.08 h ^- 1, fraction of dose absorbed by first-order (Fr) of 32.60%, duration of the zero-order absorption (Tk0) of 0.88 h with latency time (Tlag) of 0.47 h, volume of distribution of 230 l and clearance of 46.80 l h ^- 1. Bodyweight affects Tk0, dosage form was found to correlate with Tk0 and Tlag, while gender affects Tlag. However, simulations evaluating the clinical importance of these covariates on steady-state indicated minimal changes on bromopride exposure. The mixed absorption model was reasonable to describe the absorption process of bromopride because it had the flexibility to fit multiple-peaks profile and shows good agreement with physicochemical properties of drug.

Quantitative Prediction of Human Pharmacokinetics and Pharmacodynamics of CKD519, a Potent Inhibitor of Cholesteryl Ester Transfer Protein (CETP)

CKD519, a selective inhibitor of cholesteryl ester transfer protein(CETP), is undergoing development as an oral agent for the treatment of primary hypercholesterolemia and mixed hyperlipidemia. The aim of this study was to predict the appropriate efficacious dose of CKD519 for humans in terms of the inhibition of CETP activity by developing a CKD519 pharmacokinetic/pharmacodynamic (PK/PD) model based on data from preclinical studies. CKD519 was intravenously and orally administered to hamsters, rats, and monkeys for PK assessment. Animal PK models of all dose levels in each species were developed using mixed effect modeling analysis for exploration, and an interspecies model where allometric scaling was applied was developed based on the integrated animal PK data to predict the human PK profile. PD parameters and profile were predicted using in vitro potency and same-in-class drug information. The two-compartment first-order elimination model with Weibull-type absorption and bioavailability following the sigmoid E_max model was selected as the final PK model. The PK/PD model was developed by linking the interspecies PK model with the E_max model of the same-in-class drug. The predicted PK/PD profile and parameters were used to simulate the human PK/PD profiles for different dose levels, and based on the simulation result, the appropriate efficacious dose was estimated as 25 mg in a 60 kg human. However, there were some discrepancies between the predicted and observed human PK/PD profiles compared to the phase I clinical data. The huge difference between the observed and predicted bioavailability suggests that there is a hurdle in predicting the absorption parameter only from animal PK data.

Single-dose escalation study of yogliptin in healthy Chinese volunteers

BACKGROUND

Yogliptin is a novel xanthine dipeptidyl peptidase-4 (DPP-4) inhibitor targeting type 2 diabetes. After promising preclinical pharmacological studies, the first human trial of yogliptin was designed.

METHODS

A randomized, double-blind, parallel, placebo-controlled phase I single-dose escalation study was designed to evaluate the pharmacokinetics, pharmacodynamics, and tolerability after single oral doses of yogliptin in healthy Chinese subjects. Healthy subjects were assigned to nine cohorts, which received a single dose of yogliptin at 2.5, 5, 10, 25, 50, 100, 200, 400, or 600 mg. Two subjects in each cohort received placebo. Blood samples were collected before dosing and up to 192 h afterwards. Urine samples were collected until 120 h after dosing. Plasma and urine drug concentrations were determined using liquid chromatography coupled with tandem mass spectrometry, and DPP-4 activity was measured using a semi-quantitative, fluorescence-based kinetic assay.

RESULTS

A total of 104 subjects were enrolled, 103 of whom completed the study (mean age, 25.3 years; mean weight, 58.8 kg; mean BMI, 21.8 kg/m²). A total of 27 adverse events (AEs) occurred in 25 of 86 yogliptin subjects (29.1%), and 3 AEs occurred in 3 of 18 placebo subjects (16.7%). Yogliptin was absorbed with a median time of maximum observed concentration (T_max) of 3.0 h and was eliminated slowly with a t_1/2 of 25.45-43.84 h. The maximum observed concentration (C_max) and area under the curve (AUC) varied slightly more than dose-proportionally over the dose range from 2.5 to 400 mg. The fraction of drug excreted in urine ranged from 8.39% to 24.77%. Mean DPP-4 inhibition at 24 h after dosing ranged from 97.7% to 99.5%, and DPP-4 inhibition was >80% for 72 h at doses from 25 to 400 mg. DPP-4 inhibition was >80% for 1 week in the group receiving 400 mg.

CONCLUSION

Yogliptin was well tolerated in healthy subjects, with no dose-limiting toxicity observed in the range from 2.5 to 600 mg. Yogliptin inhibited plasma DPP-4 activity for 72 h at single doses of 25-200 mg and for 1 week at 400 mg, suggesting that once-weekly dosing of yogliptin is possible in type 2 diabetes patients.

TRIAL REGISTRATION

ChiCTR-IIR-17010311 (Chictr.org).

On the unphysical hypotheses in pharmacokinetics and oral drug absorption: Time to utilize instantaneous rate coefficients instead of rate constants

This work aims to explore the unphysical assumptions associated with i) the homogeneity of the well mixed compartments of pharmacokinetics and ii) the diffusion limited model of drug dissolution. To this end, we i) tested the homogeneity hypothesis using Monte Carlo simulations for a reaction and a diffusional process that take place in Euclidean and fractal media, ii) re-considered the flip-flop kinetics assuming that the absorption rate for a one-compartment model is governed by an instantaneous rate coefficient instead of a rate constant, and, iii) re-considered the extent of drug absorption as a function of dose using an in vivo reaction limited model of drug dissolution with integer and non-integer stoichiometry values. We found that drug diffusional processes and reactions are slowed down in heterogeneous media and the environmental heterogeneity leads to increased fluctuations of the measurable quantities. Highly variable experimental literature data with measurements in intrathecal space and gastrointestinal fluids were explained accordingly. Next, by applying power law and Weibull input functions to a one-compartment model of disposition we show that the shape of concentration-time curves is highly dependent on the time exponent of the input functions. Realistic examples based on PK data of three compounds known to exhibit flip-flop kinetics are analyzed. The need to use time dependent coefficients instead of rate constants in PBPK modeling and virtual bioequivalence is underlined. Finally, the shape of the fraction absorbed as a function of dose plots, using an in vivo reaction limited model of drug dissolution were found to be dependent on the stoichiometry value and the solubility of drug. Ascending and descending limbs were observed for the higher stoichiometries (2.0 and 1.5) with the low solubility drug. In contrast, for the more soluble drug, a continuous increase of fraction absorbed as a function of dose is observed when the higher stoichiometries are used (2.0 and 1.5). For both drugs, the fraction absorbed for the lower values of stoichiometry (0.7 and 1.0) exhibit a non-dependency on dose profile. Our results give an insight into the complex picture of in vivo drug dissolution since diffusion-limited and reaction-limited processes seem to operate under in vivo conditions concurrently.

Pharmacokinetics and tissue distribution of monotropein and deacetyl asperulosidic acid after oral administration of extracts from Morinda officinalis root in rats

BACKGROUND

Iridoid glycosides (IGs), including monotropein (MON) and deacetyl asperulosidic acid (DA) as the main ingredients, are the major chemical components in Morinda officinalis How. (MO) root, possessing various pharmacological properties including anti-osteoporosis, anti-inflammation and anti-rheumatism activities.The aim of the present study was to further elucidate the pharmacological actions of MO by investigating the pharmacokinetics and tissue distribution of IGs in MO.

METHODS

An ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS) method was developed and validated for simultaneous determination of MON and DA levels in plasma and various tissues of Wistar rats. MON, DA and acetaminophen (ACE) as the internal standard (IS) were extracted from rat plasma and tissue samples by direct deproteinization with methanol. The rats were administered orally at 1650 mg/kg MO and 25, 50 and 100 mg/kg MO iridoid glycosides (MOIGs) or intravenously at MOIG 25 mg/kg for pharmacokinetic study of MON and DA. In addition, 100 mg/kg MOIG was administered orally for tissue distribution study of MON and DA. Non-compartmental pharmacokinetic profiles were constructed. Tissue distributions were calculated according to the validated methods.

RESULTS

Significant differences in the pharmacokinetic parameters were observed in male and female rats. The AUC0-t, Cmax and bioavailability of MON and DA in female rats were higher than those in male rats. MON and DA mainly distributed in the intestine and stomach after oral administration, and noteworthily high concentrations of MON and DA were detected in the rat hypothalamus.

CONCLUSION

The results of the present study may shed new lights on the biological behavior of MOIGs in vivo, help explain their pharmacological actions, and provide experimental clues for rational clinical use of these IGs extracted from the MO root.

Bayesian knowledge integration for an in vitro-in vivo correlation model

The primary goal of "in vitro-in vivo correlation" (IVIVC) is the reliable prediction of the in vivo serum concentration-time course, based on the in vitro drug dissolution or release profiles. IVIVC methods are particularly appropriate for formulations that are released over an extended period of time or with a lag in absorption and may support approving a change in formulation of a drug without additional bioequivalence trials in human subjects. Most of the current IVIVC models are assessed using frequentist methods, such as linear regression, based on averaged data and entail complex and potentially unstable mathematical deconvolution. The proposed IVIVC approach includes (a) a nonlinear-mixed effects model for the in vitro release data; (b) a population pharmacokinetic (PK) compartment model for the in vivo immediate release (IR) data; and (c) a system of ordinal differential equations (ODEs), containing the submodels (a) and (b), which approximates and predicts the in vivo controlled release (CR) data. The innovation in this paper consists of splitting the parameter space between submodels (a) and (b) versus (c). Subsequently, the uncertainty on these parameters is accounted for using a Bayesian framework, that is estimates from the first two submodels serve as priors for the Bayesian hierarchical third submodel. As such, the Bayesian method explained ensures a natural integration and transfer of knowledge between various sources of information, balancing possible differences in sample size and parameter uncertainty of in vitro and in vivo studies. Consequently, it is a very flexible approach yielding results for a broad range of data situations. The application of the method is demonstrated for a transdermal patch (TD).

In silico drug absorption tract: An agent-based biomimetic model for human oral drug absorption

Background

An agent-based modeling approach has been suggested as an alternative to traditional, equation-based modeling methods for describing oral drug absorption. It enables researchers to gain a better understanding of the pharmacokinetic (PK) mechanisms of a drug. This project demonstrates that a biomimetic agent-based model can adequately describe the absorption and disposition kinetics both of midazolam and clonazepam.

Methods

An agent-based biomimetic model, in silico drug absorption tract (ISDAT), was built to mimic oral drug absorption in humans. The model consisted of distinct spaces, membranes, and metabolic enzymes, and it was altogether representative of human physiology relating to oral drug absorption. Simulated experiments were run with the model, and the results were compared to the referent data from clinical equivalence trials. Acceptable similarity was verified by pre-specified criteria, which included 1) qualitative visual matching between the clinical and simulated concentration-time profiles, 2) quantitative similarity indices, namely, weighted root mean squared error (RMSE), and weighted mean absolute percentage error (MAPE) and 3) descriptive similarity which requires less than 25% difference between key PK parameters calculated by the clinical and the simulated concentration-time profiles. The model and its parameters were iteratively refined until all similarity criteria were met. Furthermore, simulated PK experiments were conducted to predict bioavailability (F). For better visualization, a graphical user interface for the model was developed and a video is available in Supporting Information.

Results

Simulation results satisfied all three levels of similarity criteria for both drugs. The weighted RMSE was 0.51 and 0.92, and the weighted MAPE was 5.99% and 8.43% for midazolam and clonazepam, respectively. Calculated PK parameter values, including area under the curve (AUC), peak plasma drug concentration (C_max), time to reach C_max (T_max), terminal elimination rate constant (Kel), terminal elimination half life (T_1/2), apparent oral clearance (CL/F), and apparent volume of distribution (V/F), were reasonable compared to the referent values. The predicted absolute oral bioavailability (F) was 44% for midazolam (literature reported value, 31–72%) and 93% (literature reported value, ≥ 90%) for clonazepam.

Conclusion

The ISDAT met all the pre-specified similarity criteria for both midazolam and clonazepam, and demonstrated its ability to describe absorption kinetics of both drugs. Therefore, the validated ISDAT can be a promising platform for further research into the use of similar in silico models for drug absorption kinetics.

Effect of Emulsification Method and Particle Size on the Rate of in vivo Oral Bioavailability of Kenaf (Hibiscus cannabinus L.) Seed Oil

Kenaf (Hibiscus cannabinus L.) seed oil-in-water nanoemulsions stabilized by complexation of beta-cyclodextrin with sodium caseinate and Tween 20 have been shown to have higher bioaccessibility of vitamin E and total phenolic content than nonemulsified kenaf seed oil in the previous in vitro gastrointestinal digestion study. However, its oral bioavailability was unknown. Therefore, the aim of this study was to evaluate the rate of in vivo oral bioavailability of kenaf seed oil-in-water nanoemulsions in comparison with nonemulsified kenaf seed oil and kenaf seed oil macroemulsions during the 180 min of gastrointestinal digestion. Kenaf seed oil macroemulsions were produced by using conventional method. Kenaf seed oil-in-water nanoemulsions had shown improvement in the rate of absorption. At 180 min of digestion time, the total α-tocopherol bioavailability of kenaf seed oil nanoemulsions was increased by 1.7- and 1.4-fold, compared to kenaf seed oil and macroemulsion, respectively. Kenaf seed oil-in-water nanoemulsions were stable in considerably wide range of pH (>5 and <3), suggesting that it can be fortified into beverages within this pH range PRACTICAL APPLICATION: The production of kenaf seed oil-in-water nanoemulsions had provided a delivery system to encapsulate the kenaf seed oil, as well as enhanced the bioaccessibility and bioavailability of kenaf seed oil. Therefore, kenaf seed oil-in-water nanoemulsions exhibit a great potential application in nutraceutical fields.

Long-Acting Injectable Second-Generation Antipsychotics: An Update and Comparison Between Agents

Schizophrenia is a chronic medical condition with periods of remission and relapses over a patient's lifetime. Antipsychotic medications represent the mainstay of treatment for this disease. Long-acting injectable (LAI) formulations of antipsychotics are an attractive alternative to their oral counterparts, as they enhance patient adherence. A number of second-generation antipsychotics (SGAs) are available in LAI formulations. These include paliperidone, aripiprazole, olanzapine, and risperidone. This article reviews the most recently developed and approved of these formulations-aripiprazole monohydrate, aripiprazole lauroxil, and paliperidone palmitate. While all were initially available as once-monthly formulations, a paliperidone palmitate 3-monthly injection formulation has been approved and is the first LAI agent to extend the dosing administration beyond the typical monthly time period. In addition, aripiprazole lauroxil every 6-week and 8-week administration preparations have been developed. LAI preparations of the SGAs have all demonstrated superiority over placebo and are comparable to their oral counterparts in terms of safety and tolerability, if injection site reactions are not taken into account. First-generation antipsychotic LAI preparations (e.g., haloperidol decanoate) have recently been compared with SGA LAI agents, and both formulations demonstrated comparable efficacy with the expected adverse events seen with each drug. Despite their availability, barriers to the use of LAIs remain. Education of both patients and clinicians on the use of LAI formulations and the continued development of these agents are important steps in ensuring these medications are available to the patients they would be most likely to benefit.

Population Pharmacokinetics of Trimethoprim-Sulfamethoxazole in Infants and Children

Trimethoprim (TMP)-sulfamethoxazole (SMX) is used to treat various types of infections, including community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) and Pneumocystis jirovecii infections in children. Pharmacokinetic (PK) data for infants and children are limited, and the optimal dosing is not known. We performed a multicenter, prospective PK study of TMP-SMX in infants and children. Separate population PK models were developed for TMP and SMX administered by the enteral route using nonlinear mixed-effects modeling. Optimal dosing was determined on the basis of the matching adult TMP exposure and attainment of the surrogate pharmacodynamic (PD) target for efficacy, a free TMP concentration above the MIC over 50% of the dosing interval. Data for a total of 153 subjects (240 samples for PK analysis) with a median postnatal age of 8 years (range, 0.1 to 20 years) contributed to the analysis for both drugs. A one-compartment model with first-order absorption and elimination characterized the TMP and SMX PK data well. Weight was included in the base model for clearance (CL/F) and volume of distribution (V/F). Both TMP and SMX CL/F increased with age. In addition, TMP and SMX CL/F were inversely related to the serum creatinine and albumin concentrations, respectively. The exposure achieved in children after oral administration of TMP-SMX at 8/40 mg/kg of body weight/day divided into administration every 12 h matched the exposure achieved in adults after administration of TMP-SMX at 320/1,600 mg/day divided into administration every 12 h and achieved the PD target for bacteria with an MIC of 0.5 mg/liter in >90% of infants and children. The exposure achieved in children after oral administration of TMP-SMX at 12/60 and 15/75 mg/kg/day divided into administration every 12 h matched the exposure achieved in adults after administration of TMP-SMX at 640/3,200 mg/day divided into administration every 12 h in subjects 6 to <21 years and 0 to <6 years of age, respectively, and was optimal for bacteria with an MIC of up to 1 mg/liter.

Population Pharmacokinetics of a Novel Once-Every 3 Months Intramuscular Formulation of Paliperidone Palmitate in Patients with Schizophrenia

OBJECTIVES

Our objective was to characterize the population pharmacokinetics of paliperidone after intramuscular administration of its long-acting 3-month formulation palmitate ester at various doses and at different injection sites (deltoid and gluteal muscles).

METHODS

This retrospective analysis included pooled data from 651 subjects from one phase I study (single injection of the 3-month formulation) and one phase III study (multiple injections of both 1- and 3-month formulations). A total of 8990 pharmacokinetic samples with valid concentration time points were available for this analysis. Nonlinear mixed-effects modelling of the pooled data was conducted using NONMEM software. Knowledge from a previously developed 1-month formulation model was used as a starting point to build the 3-month formulation model.

RESULTS

The final model describing the plasma concentrations after administration of the 3-month formulation was a one-compartment model with first-order elimination and two saturable absorption processes (rapid and slow). The apparent volume of distribution estimated for the 3-month formulation was not the same as for the previously modelled 1-month formulation. Apparent clearance (CL), apparent volume of distribution (V), and fraction of the absorbed dose (F₃) were estimated to be 3.84 l/h, 1960 L, and 20.9 %. For slow absorption, the maximum absorption rate constant (k _{a1 max}), amount of paliperidone at the absorption site when half of the maximum absorption rate was achieved (k _{amt1 50}), and Hill factor (γ) were estimated to be 90.4 µg/h, 120 mg, and 1.44, respectively. For rapid absorption, the maximum absorption rate constant (k _{a3 max}) and amount of paliperidone at the absorption site when half of the maximum absorption rate was achieved (k _{amt3 50}) were estimated to be 164 µg/h and 21.4 mg, respectively.

CONCLUSION

The final model with two saturable absorption processes provided a good description of the pharmacokinetic characteristics of paliperidone after intramuscular administration of its long-acting 3-month formulation palmitate ester. In addition to the structural covariates (creatinine clearance on CL, body mass index on V, and injection volume on both absorption rates), injection site and sex were identified as covariates on k _{a max} of the slow absorption process (k _{a1 max}). Clinical trial registration numbers: NCT01559272, NCT01529515, and NCT01515423.

Population pharmacokinetic model of transdermal nicotine delivered from a matrix-type patch

AIMS

Nicotine addiction is an issue faced by millions of individuals worldwide. As a result, nicotine replacement therapies, such as transdermal nicotine patches, have become widely distributed and used. While the pharmacokinetics of transdermal nicotine have been extensively described using noncompartmental methods, there are few data available describing the between-subject variability in transdermal nicotine pharmacokinetics. The aim of this investigation was to use population pharmacokinetic techniques to describe this variability, particularly as it pertains to the absorption of nicotine from the transdermal patch.

METHODS

A population pharmacokinetic parent-metabolite model was developed using plasma concentrations from 25 participants treated with transdermal nicotine. Covariates tested in this model included: body weight, body mass index, body surface area (calculated using the Mosteller equation) and sex.

RESULTS

Nicotine pharmacokinetics were best described with a one-compartment model with absorption based on a Weibull distribution and first-order elimination and a single compartment for the major metabolite, cotinine. Body weight was a significant covariate on apparent volume of distribution of nicotine (exponential scaling factor 1.42). After the inclusion of body weight in the model, no other covariates were significant.

CONCLUSIONS

This is the first population pharmacokinetic model to describe the absorption and disposition of transdermal nicotine and its metabolism to cotinine and the pharmacokinetic variability between individuals who were administered the patch.

Pharmacokinetic and pharmacodynamic modelling after subcutaneous, intravenous and buccal administration of a high-concentration formulation of buprenorphine in conscious cats

Background

The aim of this study was to describe the joint pharmacokinetic-pharmacodynamic model and evaluate thermal antinociception of a high-concentration formulation of buprenorphine (Simbadol^™) in cats.

Methods

Six healthy cats (4.9 ± 0.7 kg) were included in a prospective, randomized, blinded, crossover study. Simbadol^™ (1.8 mg mL^-1) was administered by the subcutaneous (SC; 0.24 mg kg^-1), intravenous (IV; 0.12 mg kg^-1) or buccal (OTM; 0.12 mg kg^-1) route of administration and thermal thresholds (TT) were compared with a saline group (SAL). Thermal threshold testing and blood sampling were performed at predetermined time points up to 72 hours including a placebo group. Plasma buprenorphine and norbuprenorphine concentrations were measured using liquid chromatography mass spectrometry. A bespoke bicompartmental pharmacokinetic model simultaneously fitted data from two analytes/three routes of administration. Temporal changes in TT were analyzed using one-way ANOVA followed by Dunnett’s test and treatment comparisons using two-way ANOVA with Bonferroni’s correction (P < 0.05).

Results

Thermal thresholds were significantly increased after SC, IV and OTM from 1–24 hours (except 2 hours), 0.5–8 hours (except 6 hours), and 1–8 hours (except 6 hours), respectively, when compared with baseline. Thermal thresholds were significantly increased after SC (1–30 hours), IV (1–8 hours) and OTM (1–12 hours) when compared with SAL, but not different among buprenorphine-treated cats. The absolute buprenorphine clearance was 0.98 L kg^-1 hour^-1, volume of distribution at steady state was 7.9 L kg^-1 and the elimination-half-life was 12.3 hours. Bioavailability for SC and OTM was 94% and 24%, respectively. Subcutaneous absorption was biphasic. An initial peak (0.08 hours) was followed by a slow (half-life 11.2 hours) and progressive (peak acceleration at 2.8 hours) uptake.

Conclusion

The SC administration of Simbadol^™ was characterized by prolonged absorption half-life and sustained plasma concentrations yielding long-lasting antinociception (≥ 24 hours) when compared with the IV and OTM routes.

Exploring Canine-Human Differences in Product Performance. Part II: Use of Modeling and Simulation to Explore the Impact of Formulation on Ciprofloxacin In Vivo Absorption and Dissolution in Dogs

This study explored the in vivo performance of three oral ciprofloxacin formulations (oral solution, fast, or slow dissolving tablets) in beagle dogs. The in vivo absorption and dissolution behaviors, estimated with in silico mechanistic models, were compared to the results previously published in human volunteers. Six normal healthy male beagle dogs (five to completion) received three oral formulations and an intravenous infusion in a randomized crossover design. Plasma ciprofloxacin concentrations were estimated by tandem mass spectrometry detection. A mechanistic absorption model was used to predict the in vivo dissolution and absorption characteristics of the oral formulations. Canine ciprofloxacin absorption was constrained to the duodenum/jejunum. This absorption window was far narrower than that seen in humans. Furthermore, while substantial within-individual variability in drug absorption was seen in human subjects, a greater magnitude of variability was observed in dogs. For three sets of data, a lag time in gastric emptying was necessary to improve the accuracy of model-generated in vivo blood level profile predictions. In addition to species-associated dissimilarities in drug solubilization due to human versus canine differences in gastrointestinal fluid compositions, the far more rapid intestinal transit time and potential segmental differences in drug absorption needed to be considered during human-canine extrapolation of oral drug and drug product performance. Through the use of mechanistic models, the data generated in the human and canine studies contributed insights into some aspects of the interspecies differences to be considered when extrapolating oral bioavailability/formulation effect data between dogs and humans.

An allometric pharmacokinetic/pharmacodynamics model for BI 893923, a novel IGF-1 receptor inhibitor

PURPOSE

BI 893923 is a novel IGF1R/INSR inhibitor with promising anti-tumor efficacy. Dose-limiting hyperglycemia has been observed for other IGF1R/INSR inhibitors in clinical trials. To counterbalance anti-tumor efficacy with the risk of hyperglycemia and to determine the therapeutic window, we aimed to develop a translational pharmacokinetic/pharmacodynamics model for BI 893923. This aimed to translate pharmacokinetics and pharmacodynamics from animals to humans by an allometrically scaled semi-mechanistic model.

METHODS

Model development was based on a previously published PK/PD model for BI 893923 in mice (Titze et al., Cancer Chemother Pharmacol 77:1303-1314, 13). PK and blood glucose parameters were scaled by allometric principles using body weight as a scaling factor along with an estimation of the parameter exponents. Biomarker and tumor growth parameters were extrapolated from mouse to human using the body weight ratio as scaling factor.

RESULTS

The allometric PK/PD model successfully described BI 893923 pharmacokinetics and blood glucose across mouse, rat, dog, minipig, and monkey. BI 893923 human exposure as well as blood glucose and tumor growth were predicted and compared for different dosing scenarios. A comprehensive risk-benefit analysis was conducted by determining the net clinical benefit for each schedule. An oral dose of 2750 mg BI 893923 divided in three evenly distributed doses was identified as the optimal human dosing regimen, predicting a tumor growth inhibition of 90.4% without associated hyperglycemia.

CONCLUSION

Our model supported human therapeutic dose estimation by rationalizing the optimal efficacious dosing regimen with minimal undesired effects. This modeling approach may be useful for PK/PD scaling of other IGF1R/INSR inhibitors.

Pharmacokinetics of Lidocaine Hydrochloride Administered with or without Adrenaline for the Paravertebral Brachial Plexus Block in Dogs

Adrenaline is known to prolong the duration of local anesthesia but its effects on the pharmacokinetic processes of local anesthetic drugs are not fully understood. Our objective was to develop a compartmental model for quantification of adrenaline’s impact on the pharmacokinetics of perineurally-injected lidocaine in the dog. Dogs were subjected to paravertebral brachial plexus block using lidocaine alone or adrenalinated lidocaine. Data was collected through a prospective, randomised, blinded crossover protocol performed over three periods. Blood samples were collected during 180 minutes following block execution. Compartmental pharmacokinetic models were developed and their goodness-of-fit were compared. The lowering effects of adrenaline on the absorption of lidocaine were statistically determined with one-sided tests. A one-compartment disposition model with two successive zero-order absorption processes best fitted our experimental data. Adrenaline decreased the peak plasma lidocaine concentration by approximately 60% (P < 0.001), decreased this local anesthetic’s fast and slow zero-order absorption rates respectively by 50% and 90% (P = 0.046, and P < 0.001), which respective durations were prolonged by 90% and 1300% (P < 0.020 and P < 0.001). Lidocaine demonstrated a previously unreported atypical absorption profile following its paravertebral injection in dogs. Adrenaline decreased the absorption rate of lidocaine and prolonged the duration of its absorption.

Comparative Absorption Profiles of Divalproex Sodium Delayed-Release Versus Extended-Release Tablets—Clinical Implications

Background:

The distinct absorption characteristics of the conventional enteric-coated, delayed-release (DR) and the novel extended-release (ER) divalproex sodium formulations are not well recognized.

Objective:

To quantitatively and qualitatively differentiate the absorption characteristics of divalproex-DR and -ER formulations.

Methods:

Healthy volunteers (N = 28) received single 1000 mg doses of divalproex-DR and divalproex-ER tablets in a crossover fashion. Noncompartmental and compartmental analyses were used to estimate valproic acid (VPA) pharmacokinetics from the plasma concentration–time profiles determined from intensive blood sampling over 48 hours.

Results:

VPA was not absorbed from divalproex-DR in the first 2 hours (absorption lag-time) after dosing. After VPA release in the intestine, approximately 63% of the dose was absorbed in less than 1 hour, that is, 2.9 hours (mean absorption time) from dosing. Maximum concentration (Cmax) was achieved approximately 4 hours after dosing. VPA absorption was complete (~93% of dose) within 3 absorption half-lives (~4.5 h) post-absorption lag-time, that is, 6–7 hours from dosing. In contrast, VPA absorption from divalproex-ER starts immediately after administration, initially at a modest rate, followed by slow and extended absorption at a constant rate for more than 20 hours; VPA concentrations at 1 and 2 hours were 28% and 40% of Cmax. Approximately 53% of the dose was absorbed within 12 hours (mean absorption time); complete absorption occurred over more than 20 hours without any dose dumping.

Conclusions:

When antihypertensive treatment options are clinically equivalent, prescribers may first consider using a verapamil SR–based strategy, especially in patients with CAD who have no history of depression. VPA absorption from enteric-coated divalproex-DR is rapid following a lag-time of approximately 2 hours and is complete within 6–7 hours of dosing. In contrast, VPA absorption from divalproex-ER starts immediately after administration, but occurs at a slow, approximately constant rate over more than 20 hours.

Development and validation of an UPLC-Q/TOF-MS assay for the quantitation of neopanaxadiol in beagle dog plasma: Application to a pharmacokinetic study

Neopanaxadiol (NPD), the main panaxadiol constituent of Panax ginseng C. A. Meyer (Araliaceae), has been regarded as the active component for the treatment of Alzheimer's disease. However, few references are available about pharmacokinetic evaluation for NPD. Accordingly, a rapid and sensitive method for quantitative analysis of NPD in beagle dog plasma based on ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry was developed and validated. Analytes were extracted from plasma by liquid-liquid extraction and chromatographic separation was achieved on an Agilent Zorbax Stable Bond C₁₈ column. Detection was performed in the positive ion mode using multiple reaction monitoring of the transitions both at m/z 461.4 → 425.4 for NPD and internal standard of panaxadiol. All validation parameters, such as lower limit of quantitation, linearity, specificity, precision, accuracy, extraction recovery, matrix effect and stability, were within acceptable ranges and the method was appropriate for multitude sample determination. After oral intake, NPD was slowly absorbed and eliminated from circulatory blood system and corresponding plasma exposure was low. Application of this quantitative method will yield the first pharmacokinetic profile after oral administration of NPD to beagle dog. The information obtained here will be useful to understand the pharmacological effects of NPD.

A Novel Method for Studying the Pharmacokinetics of [(14) C]Umeclidinium After Application to the Axilla or Palm of Healthy Male Subjects

Umeclidinium (UMEC), a long-acting muscarinic antagonist approved for chronic obstructive pulmonary disease (COPD), was investigated for primary hyperhidrosis as topical therapy. This study evaluated the pharmacokinetics, safety, and tolerability of a single dose of [(14) C]UMEC applied to either unoccluded axilla (UA), occluded axilla (OA), or occluded palm (OP) of healthy males. After 8 h the formulation was removed. [(14) C]UMEC plasma concentrations (Cp) were quantified by accelerator mass spectrometry. Occlusion increased systemic exposure by 3.8-fold. Due to UMEC absorption-limited pharmacokinetics, Cp data from the OA were combined with intravenous data from a phase I study. The data were described by a two-compartment population model with sequential zero and first-order absorption and linear elimination. Simulated systemic exposure following q.d. doses to axilla was similar to the exposure from the inhaled therapy, suggesting that systemic safety following dermal administration can be bridged to the inhaled program, and offering the potential for a reduced number of studies and/or subjects.

Slow drug delivery decreased total body clearance and altered bioavailability of immediate- and controlled-release oxycodone formulations

Oxycodone is a commonly used analgesic with a large body of pharmacokinetic data from various immediate-release or controlled-release formulations, under different administration routes, and in diverse populations. Longer terminal half-lives from extravascular administration as compared to IV administration have been attributed to flip-flop pharmacokinetics with the rate constant of absorption slower than elimination. However, PK parameters from the extravascular studies showed faster absorption than elimination. Sustained release formulations guided by the flip-flop concept produced mixed outcomes in formulation development and clinical studies. This research aims to develop a mechanistic knowledge of oxycodone ADME, and provide a consistent interpretation of diverging results and insight to guide further extended release development and optimize the clinical use of oxycodone. PK data of oxycodone in human studies were collected from literature and digitized. The PK data were analyzed using a new PK model with Weibull function to describe time-varying drug releases/ oral absorption, and elimination dependent upon drug input to the portal vein. The new and traditional PK models were coded in NONMEM. Sensitivity analyses were conducted to address the relationship between rates of drug release/absorption and PK profiles plus terminal half-lives. Traditional PK model could not be applied consistently to describe drug absorption and elimination of oxycodone. Errors were forced on absorption, elimination, or both parameters when IV and PO profiles were fitted separately. The new mechanistic PK model with Weibull function on absorption and slower total body clearance caused by slower absorption adequately describes the complex interplay between oxycodone absorption and elimination in vivo. Terminal phase of oxycodone PK profile was shown to reflect slower total body drug clearance due to slower drug release/absorption from oral formulations. Mechanistic PK models with Weibull absorption functions, and release rate-dependent saturable total body clearance well described the diverging oxycodone absorption and elimination kinetics in the literature. It showed no actual drug absorption during the terminal phase, but slower drug clearance caused by slower release/absorption producing the appearance of flip-flop and offered new insight for the development of modified release formulations and clinical use of oxycodone.

Population PK-PD Model for Tolerance Evaluation to the p38 MAP Kinase Inhibitor BCT197

The p38 mitogen‐activated protein kinase (p38) is a key signaling pathway involved in regulation of inflammatory cytokines. Unexpectedly, several clinical studies using p38 inhibitors found no convincing clinical efficacy in the treatment of chronic inflammation. It was the objective of this study to characterize the population pharmacokinetics (PK) of BCT197 in healthy volunteers and to examine the relationship between BCT197 exposure and pharmacodynamics (PD) measured as inhibition of ex vivo lipopolysaccharide (LPS)‐induced tumor necrosis factor alpha (TNFα), a downstream marker of p38 activity. PK was characterized using a two‐compartment model with mixed‐order absorption and limited‐capacity tissue binding. The PK‐PD relationship revealed that suppression of TNFα was partly offset over time, despite continuous drug exposure. This may indicate a mechanism by which the inflammatory response acquires the ability to bypass p38. Simulations of posology dependence in drug effect suggest that an intermittent regimen may offer clinical benefit over continuous dosing and limit the impact of tolerance development.

Anemarrhena asphodeloides Non-Steroidal Saponin Components Alter the Pharmacokinetic Profile of Its Steroidal Saponins in Rat

A rapid, selective and sensitive UPLC-MS/MS assay was established to determine the plasma concentrations of four steroidal saponins. Sprague-Dawley rats were allocated to four groups which were orally administered Anemarrhena asphodeloides extracts (ASE), ASE combined with macromolecular fraction (ASE-MF), ASE combined with small molecule fraction (ASE-SF) and ASE combined with small molecule and macromolecular fraction (ASE-SF-MF) containing approximately the same dose of ASE. At different time points, the concentration of timosaponin BII, anemarsaponin BIII, timosaponin AIII and timosaponin E1 in rat plasma were determined and main pharmacokinetic parameters including Cmax, Tmax, T1/2, AUC were calculated using the DAS 3.2 software package. The statistical analysis was performed using the Student's t-test with p < 0.05 as the level of significance. MF had no effect on the pharmacokinetic behaviors and parameters of four steroidal saponins. It was found that Cmax and AUC of four steroidal saponins in group ASE-SF and ASE-SF-MF, were significantly increased compared with those in group ASE. These results indicate that SF in A. asphodeloides extracts could increase the absorption and improve the bioavailability of the steroidal saponins.

Incorporation of stochastic variability in mechanistic population pharmacokinetic models: handling the physiological constraints using normal transformations

The utilisation of physiologically-based pharmacokinetic models for the analysis of population data is an approach with progressively increasing impact. However, as we move from empirical to complex mechanistic model structures, incorporation of stochastic variability in model parameters can be challenging due to the physiological constraints that may arise. Here, we investigated the most common types of constraints faced in mechanistic pharmacokinetic modelling and explored techniques for handling them during a population data analysis. An efficient way to impose stochastic variability on the parameters of interest without neglecting the underlying physiological constraints is through the assumption that they follow a distribution with support and properties matching the underlying physiology. It was found that two distributions that arise through transformations of the normal, the logit-normal generalisation and the logistic-normal, are excellent for such an application as not only they can satisfy the physiological constraints but also offer high flexibility during characterisation of the parameters' distribution. The statistical properties and practical advantages/disadvantages of these distributions for such an application were clearly displayed in the context of different modelling examples. Finally, a simulation study clearly illustrated the practical gains of the utilisation of the described techniques, as omission of population variability in physiological systems parameters leads to a biased/misplaced stochastic model with mechanistically incorrect variance structure. The current methodological work aims to facilitate the use of mechanistic/physiologically-based models for the analysis of population pharmacokinetic clinical data.