Population pharmacokinetic model to analyze nevirapine multiple-peaks profile after a single oral dose

Implications of Bariatric Surgery on the Pharmacokinetics of Antiretrovirals in People Living with HIV

Bariatric surgery is increasingly applied among people living with HIV to reduce obesity and the associated morbidity and mortality. In people living with HIV, sufficient antiretroviral exposure and activity should always be maintained to prevent development of resistance and disease progression. However, bariatric surgery procedures bring various gastrointestinal modifications including changes in gastric volume, and acidity, gastrointestinal emptying time, enterohepatic circulation and delayed entry of bile acids. These alterations may affect many aspects of antiretroviral pharmacokinetics. Some drug characteristics may result in subtherapeutic exposure and the potential related risk of treatment failure and resistance. Antiretrovirals that require low pH, administration of fatty meals, longer intestinal exposure, and an enterohepatic recirculation for their absorption may be most impacted by bariatric surgery procedures. Additionally, some antiretrovirals can interact with the polyvalent cations in supplements or drugs inhibiting gastric acid, thereby preventing their use as these comedications are commonly prescribed post-bariatric surgery. Predicting pharmacokinetics on the basis of drug characteristics solely proved to be challenging, therefore pharmacokinetic studies remain crucial in this population. Here, we discuss general implications of bariatric surgery on antiretroviral outcomes in people living with HIV as well as drug properties that are relevant for the choice of antiretroviral treatment in this special patient population. Additionally, we summarise studies that evaluated the pharmacokinetics of antiretrovirals post-bariatric surgery. Finally, we performed a comprehensive analysis of theoretical considerations and published pharmacokinetic and pharmacodynamic data to provide recommendations on antiretrovirals for people living with HIV undergoing bariatric surgery.

On the population pharmacokinetics and the enterohepatic recirculation of hyzetimibe and its main metabolite in Chinese healthy subjects

BACKGROUNDS

Hyzetimibe (HS-25), a new drug approved for hypercholesterolemia, exhibits obvious enterohepatic recirculation (EHC) after oral administration. Up to now, little is known about the kinetics of HS-25. Therefore, we performed this population pharmacokinetic (PopPK) analysis aiming to describe the PK behavior of HS-25 and its main metabolite (M1), and to identify significant covariates contributing to the variability.

METHODS

The plasma concentration data used for modeling were obtained from an open-label, single-dose, randomized, two-period crossover bioequivalence study. PopPK modeling was performed with NONMEM 7.4.1 using nonlinear mixed effect modeling approach. Goodness of fit plots, bootstrap and visual predictive check were used for model internal validation. Data from another study was used for external validation.

RESULTS

Data from 16 male and 8 female subjects were used in the PopPK analysis. HS-25 and M1 concentrations in the modeling cohort were well described by a one-compartment model incorporating first-pass metabolism and a gallbladder compartment, accounting for the EHC process. The release kinetic of gall was mimicked by a first-order constant plus a switch on/off effect. Body weight was identified as a significant covariate effecting on the clearance and apparent distribution volume of HS-25, as well as k_mg , the transfer rate from metabolite compartment to gallbladder compartment. Internal and external validation demonstrated an acceptable predictive ability of the final model.

CONCLUSIONS

We present the first PopPK model describing HS-25 and M1 concentrations simultaneously, with the EHC process considered. The modeling and simulation results could provide reference for the clinical use of HS-25.

Determination of Verapamil Hydrochloride and Norverapamil Hydrochloride in Rat Plasma by Capillary Electrophoresis With End-Column Electrochemiluminescence Detection and Their Pharmacokinetics Study

In this study, we developed a new method for simultaneous determination of verapamil hydrochloride (VerHCl) and its metabolite norverapamil hydrochloride (NorHCl) by using the capillary electrophoresis-electrochemiluminescence. Under optimized experimental conditions, the linear ranges of the VerHCl and NorHCl concentrations were 0.015-10.0 and 0.060-10.0 μg/mL, respectively. The linearity relations were determined using the respective regression equations y = 581.2x + 19.94 and y = 339.4x + 29.16. The respective limits of detection (S/N = 3) were 0.006 and 0.024 μg/mL. The proposed method was used to study the pharmacokinetics of both agents in rat plasma. The maximum concentration (Cmax), half-life time (T1/2) and time to peak (Tmax) were 683.21 ± 74.81 ng/mL, 0.52 ± 0.21 h and 2.49 ± 0.32 h for VerHCl and 698.42 ± 71.45 ng/mL, 1.14 ± 0.26 h and 2.83 ± 0.23 h for NorHCl, respectively, following oral administration of 10 mg/kg VerHCl.

Enteric reabsorption processes and their impact on drug pharmacokinetics

Enteric reabsorption occurs when a drug is secreted into the intestinal lumen and reabsorbed into the systemic circulation. This distribution process is evidenced by multiple peaks in pharmacokinetic profiles. Commonly, hepatobiliary drug secretion is assumed to be the underlying mechanism (enterohepatic reabsorption, EHR), neglecting other possible mechanisms such as gastric secretion (enterogastric reabsorption, EGR). In addition, the impact of drug reabsorption on systemic clearance, volume of distribution and bioavailability has been a subject of long-standing discussions. In this work, we propose semi-mechanistic pharmacokinetic models to reflect EHR and EGR and compare their respective impact on primary pharmacokinetic parameters. A simulation-based analysis was carried out considering three drug types with the potential for reabsorption, classified according to their primary route of elimination and their hepatic extraction: (A) hepatic metabolism-low extraction; (B) hepatic metabolism-intermediate/high extraction; (C) renal excretion. Results show that an increase in EHR can significantly reduce the clearance of drugs A and B, increase bioavailability of B drugs, and increase the volume of distribution for all drugs. Conversely, EGR had negligible impact in all pharmacokinetic parameters. Findings provide background to explain and forecast the role that this process can play in pharmacokinetic variability, including drug-drug interactions and disease states.

Singularities of nevirapine metabolism: from sex-dependent differences to idiosyncratic toxicity

Nevirapine (NVP) is a first-generation non-nucleoside reverse transcriptase inhibitor widely used for the treatment and prophylaxis of human immunodeficiency virus infection. The drug is taken throughout the patient's life and, due to the availability of an extended-release formulation, it is administered once daily. This antiretroviral is one of the scarce examples of drugs with prescription criteria based on sex, in order to prevent adverse reactions. The therapy with NVP has been associated with potentially life-threatening liver and idiosyncratic skin toxicity. Multiple evidence has emerged regarding the formation of electrophilic NVP metabolites as crucial for adverse idiosyncratic reactions. The formation of reactive metabolites that yield covalent adducts with proteins has been demonstrated in patients under NVP-based treatment. Interestingly, several pharmacogenetic- and sex-related factors associated with NVP toxicity can be mechanistically explained by an imbalance toward increased formation of NVP-derived reactive metabolites and/or impaired detoxification capability. Moreover, the haptenation of self-proteins by these reactive species provides a plausible link between NVP bioactivation and immunotoxicity, further supporting the relevance of this toxicokinetics hypothesis. In the current paper, we review the existing knowledge and recent developments on NVP metabolism and their relation to NVP toxicity.

A Physiologically-Based Pharmacokinetic Model to Predict Human Fetal Exposure for a Drug Metabolized by Several CYP450 Pathways

BACKGROUND

Pregnant women and their fetuses are exposed to numerous drugs; however, they are orphan populations with respect to the safety and efficacy of drugs. Therefore, the prediction of maternal and fetal drug exposure prior to administration would be highly useful.

METHODS

A physiologically-based pharmacokinetic (PBPK) model for nevirapine, which is metabolized by the cytochrome P450 (CYP) 3A4, 2B6 and 2D6 pathways, was developed to predict maternal and fetal pharmacokinetics (PK). The model was developed in both non-pregnant and pregnant women, and all physiological and enzymatic changes that could impact nevirapine PK were taken into account. Transplacental parameters estimated from ex vivo human placenta perfusion experiments were included in this PBPK model. To validate the model, observed maternal and cord blood concentrations were compared with predicted concentrations, and the impact of fetal clearance on fetal PK was investigated.

RESULTS

By implementing physiological changes, including CYP3A4, 2D6 and 2B6 inductions, we predicted a clearance increase of 21 % in late pregnancy. The PBPK model successfully predicted the disposition for both non-pregnant and pregnant populations. Parameters obtained from the ex vivo experiments allowed the prediction of nevirapine concentrations that matched observed cord blood concentrations. The fetal-to-maternal area under the curve ratio (0-24 h interval) was 0.77, and fetal metabolism had no significant effect on fetal PK.

CONCLUSIONS

The PBPK approach is a useful tool for quantifying a priori the drug exposure of metabolized drugs during pregnancy, and can be applied to evaluate alternative dosing regimens to optimize drug therapy. This approach, including ex vivo human placental perfusion parameters, is a promising approach for predicting human fetal exposure.

Role of enterohepatic recirculation in drug disposition: cooperation and complications

Enterohepatic recirculation (EHC) concerns many physiological processes and notably affects pharmacokinetic parameters such as plasma half-life and AUC as well as estimates of bioavailability of drugs. Also, EHC plays a detrimental role as the compounds/drugs are allowed to recycle. An in-depth comprehension of this phenomenon and its consequences on the pharmacological effects of affected drugs is important and decisive in the design and development of new candidate drugs. EHC of a compound/drug occurs by biliary excretion and intestinal reabsorption, sometimes with hepatic conjugation and intestinal deconjugation. EHC leads to prolonged elimination half-life of the drugs, altered pharmacokinetics and pharmacodynamics. Study of the EHC of any drug is complicated due to unavailability of the apposite model, sophisticated procedures and ethical concerns. Different in vitro and in vivo methods for studies in experimental animals and humans have been devised, each having its own merits and demerits. Involvement of the different transporters in biliary excretion, intra- and inter-species, pathological and biochemical variabilities obscure the study of the phenomenon. Modeling of drugs undergoing EHC has always been intricate and exigent models have been exploited to interpret the pharmacokinetic profiles of drugs witnessing multiple peaks due to EHC. Here, we critically appraise the mechanisms of bile formation, factors affecting biliary drug elimination, methods to estimate biliary excretion of drugs, EHC, multiple peak phenomenon and its modeling.

Sex-by-formulation interaction assessed through a bioequivalence study of efavirenz tablets

Although sex-related differences in gastrointestinal physiology have been vastly reported, its impact on drug oral bioavailability and bioequivalence (product discrimination) is often ignored. On this work results from an average bioequivalence study between tablets containing 600mg of the antiretroviral efavirenz (EFV), carried out with 14 healthy subjects (8 female and 6 men) in a randomized 2-period, 2-treatment crossover design, are analyzed from a sex-based approach. Sequences were balanced within each sex group. Considering all subjects, no differences were observed on EFV absorbed amount, as shown by the estimated 90CI of the AUC96 Test/Reference bioequivalence ratio (T/R): 0.950-1.05. However, results were not conclusive due to the 90CI for CMAX T/R was 0.743-1.07. Over this parameter, a significant sex-by-formulation interaction was detected: 90CI CMAX T/R was 0.838-1.36 in women and 0.540-0.920 in men; with a 52% relative difference between point estimates. Formulation differences were therefore evidenced only by male subjects. In vitro dissolution and disintegration tests for both products were carried out in two aqueous media: A) SLS 0.25% and B) HCl/KCl pH1.2. T/R results for dissolution efficiency and tablet disintegration times of formulations in both A and B media were highly correlated with CMAX T/R bioequivalence results observed in women and men respectively, showing that a dissimilar gastrointestinal environment between sexes affected EFV oral absorption. This work shows how sex-by-formulation interaction can affect bioequivalence conclusions. Sex effect on product discrimination should be specially disclosed in bioequivalence studies, mainly for drugs aimed to be given to both sexes.

Population Pharmacokinetic Modeling of the Enterohepatic Recirculation of Fimasartan in Rats, Dogs, and Humans

Enterohepatic recirculation (EHC) can greatly enhance plasma drug exposures and therapeutic effects. This study aimed to develop a population pharmacokinetic model that can simultaneously characterize the extent and time-course of EHC in three species using fimasartan, a novel angiotensin II receptor blocker, as a model drug. All fimasartan plasma concentration profiles in 32 rats (intravenous doses, 0.3-3 mg/kg; oral doses, 1-10 mg/kg), 34 dogs (intravenous doses, 0.3-1 mg/kg; oral doses, 1-10 mg/kg), and 42 healthy volunteers (single or multiple oral doses, 20-480 mg) were determined via liquid chromatography-tandem mass spectrometry (LC-MS/MS) and simultaneously modeled in S-ADAPT. The proposed model quantitatively characterized EHC in three species after oral and intravenous dosing. The median (range) fraction of drug undergoing recirculation was 76.3% (64.9-88.7%) in rats, 33.3% (24.0-45.9%) in dogs, and 65.6% (56.5-72.0%) in humans. In the presence compared with the absence of EHC, the area under the curve in plasma was predicted to be 4.22-fold (2.85-8.85) as high in rats, 1.50-fold (1.32-1.85) in dogs, and 2.91-fold (2.30-3.57) in humans. The modeled oral bioavailability in rats (median (range), 38.7% (20.0-59.8%)) and dogs (median, 7.13% to 15.4%, depending on the formulation) matched the non-compartmental estimates well. In humans, the predicted oral bioavailability was 25.1% (15.1-43.9%) under fasting and 18.2% (12.2-31.0%) under fed conditions. The allometrically scaled area under the curve predicted from rats was 420 ng·h/mL for 60 mg fimasartan compared with 424 ± 63 ng·h/mL observed in humans. The developed population pharmacokinetic model can be utilized to characterize the impact of EHC on plasma drug exposure in animals and humans.