Effect of widely used combinations of antiretroviral therapy on liver CYP3A4 activity in HIV-infected patients

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

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

An Individual Participant Data Population Pharmacokinetic Meta-analysis of Drug-Drug Interactions between Lumefantrine and Commonly Used Antiretroviral Treatment

Treating malaria in HIV-coinfected individuals should consider potential drug-drug interactions. Artemether-lumefantrine is the most widely recommended treatment for uncomplicated malaria globally. Lumefantrine is metabolized by CYP3A4, an enzyme that commonly used antiretrovirals often induce or inhibit. A population pharmacokinetic meta-analysis was conducted using individual participant data from 10 studies with 6,100 lumefantrine concentrations from 793 nonpregnant adult participants (41% HIV-malaria-coinfected, 36% malaria-infected, 20% HIV-infected, and 3% healthy volunteers).

Treating malaria in HIV-coinfected individuals should consider potential drug-drug interactions. Artemether-lumefantrine is the most widely recommended treatment for uncomplicated malaria globally. Lumefantrine is metabolized by CYP3A4, an enzyme that commonly used antiretrovirals often induce or inhibit. A population pharmacokinetic meta-analysis was conducted using individual participant data from 10 studies with 6,100 lumefantrine concentrations from 793 nonpregnant adult participants (41% HIV-malaria-coinfected, 36% malaria-infected, 20% HIV-infected, and 3% healthy volunteers). Lumefantrine exposure increased 3.4-fold with coadministration of lopinavir-ritonavir-based antiretroviral therapy (ART), while it decreased by 47% with efavirenz-based ART and by 59% in the patients with rifampin-based antituberculosis treatment. Nevirapine- or dolutegravir-based ART and malaria or HIV infection were not associated with significant effects. Monte Carlo simulations showed that those on concomitant efavirenz or rifampin have 49% and 80% probability of day 7 concentrations <200 ng/ml, respectively, a threshold associated with an increased risk of treatment failure. The risk of achieving subtherapeutic concentrations increases with larger body weight. An extended 5-day and 6-day artemether-lumefantrine regimen is predicted to overcome these drug-drug interactions with efavirenz and rifampin, respectively.

Managing antiretroviral therapy in the elderly HIV patient

Introduction: Owing to more effective and less toxic antiretroviral therapy (ART), people living with HIV (PLWH) live longer, a phenomenon expected to grow in the next decades. With advancing age, effectively treated PLWH experience not only a heightened risk for non-infective comorbidities and multimorbidity, but also for geriatric syndromes and frailty. In addition, older adults living with HIV (OALWH) have a higher prevalence of so-called iatrogenic triad described as polypharmacy (PP), potentially inappropriate medication use, and drug-drug interactions. Areas covered: This review will focus the management of ART in OALWH. We will discuss iatrogenic triad and best way to address PP. Special focus will be given to pharmacokinetic and pharmacodynamic aspects of ART in the elderly, evaluation of ART toxicities, and specific ART strategies commonly used in this population. Expert commentary: Research should be focused on recruiting more OALWH, frail individuals in particular, into the clinical trials and specific geriatric outcome need to be considered together with traditional viroimmunological outcomes.

Confirming model-predicted pharmacokinetic interactions between bedaquiline and lopinavir/ritonavir or nevirapine in patients with HIV and drug-resistant tuberculosis

Bedaquiline and its metabolite M2 are metabolised by CYP3A4. The antiretrovirals ritonavir-boosted lopinavir (LPV/r) and nevirapine inhibit and induce CYP3A4, respectively. Here we aimed to quantify nevirapine and LPV/r drug-drug interaction effects on bedaquiline and M2 in patients co-infected with HIV and multidrug-resistant tuberculosis (MDR-TB) using population pharmacokinetic (PK) analysis and compare these with model-based predictions from single-dose studies in subjects without TB. An observational PK study was performed in three groups of MDR-TB patients during bedaquiline maintenance dosing: HIV-seronegative patients (n = 17); and HIV-infected patients using antiretroviral therapy including nevirapine (n = 17) or LPV/r (n = 14). Bedaquiline and M2 samples were collected over 48 h post-dose. A previously developed PK model of MDR-TB patients was used as prior information to inform parameter estimation using NONMEM. The model was able to describe bedaquiline and M2 concentrations well, with estimates close to their priors and earlier model-based interaction effects from single-dose studies. Nevirapine changed bedaquiline clearance to 82% (95% CI 67-99%) and M2 clearance to 119% (92-156%) of their original values, indicating no clinically significant interaction. LPV/r substantially reduced bedaquiline clearance to 25% (17-35%) and M2 clearance to 59% (44-69%) of original values. This work confirms earlier model-based predictions of nevirapine and LPV/r interaction effects on bedaquiline and M2 clearance from subjects without TB in single-dose studies, in MDR-TB/HIV co-infected patients studied here. To normalise bedaquiline exposure in patients with concomitant LPV/r therapy, an adjusted bedaquiline dosing regimen is proposed for further study.

The influence of nevirapine and efavirenz-based anti-retroviral therapy on the pharmacokinetics of lumefantrine and anti-malarial dose recommendation in HIV-malaria co-treatment

Background

HIV-malaria co-infected patients in most parts of sub-Saharan Africa are treated with both artemether-lumefantrine (AL) and efavirenz (EFV) or nevirapine (NVP)-based antiretroviral therapy (ART). EFV, NVP, artemether and lumefantrine are substrates, inhibitors or inducers of CYP3A4 and CYP2B6, creating a potential for drug-drug interactions. The effect of EFV and/or NVP on lumefantrine pharmacokinetic profile among HIV-malaria co-infected patients on ART and treated with AL was investigated. Optimal lumefantrine dosage regimen for patients on EFV-based ART was determined by population pharmacokinetics and simulation.

Methods

This was a non-randomized, open label, parallel, prospective cohort study in which 128, 66 and 75 HIV-malaria co-infected patients on NVP-based ART (NVP-arm), EFV-based ART (EFV-arm) and ART naïve (control-am) were enrolled, respectively. Patients were treated with AL and contributed sparse venous plasma samples. Pharmacokinetic analysis of lumefantrine was done using non-linear mixed effect modelling.

Results

Of the evaluated models, a two-compartment pharmacokinetic model with first order absorption and lag-time described well lumefantrine plasma concentrations time profile. Patients in the EFV-arm but not in the NVP-arm had significantly lower lumefantrine bioavailability compared to that in the control-arm. Equally, 32% of patients in the EFV-arm had day-7 lumefantrine plasma concentrations below 280 ng/ml compared to only 4% in the control-arm and 3% in the NVP-arm. Upon post hoc simulation of lumefantrine exposure, patients in the EFV-arm had lower exposure (median (IQR)) compared to that in the control-arm; AUC_0-inf; was 303,130 (211,080–431,962) versus 784,830 (547,405–1,116,250); day-7 lumefantrine plasma concentrations was: 335.5 (215.8-519.5) versus 858.7 (562.3-1,333.8), respectively. The predictive model through simulation of lumefantrine exposure at different dosage regimen scenarios for patients on EFV-based ART, suggest that AL taken twice daily for five days using the current dose could improve lumefantrine exposure and consequently malaria treatment outcomes.

Conclusions

Co-treatment of AL with EFV-based ART but not NVP-based ART significantly reduces lumefantrine bioavailability and consequently total exposure. To ensure adequate lumefantrine exposure and malaria treatment success in HIV-malaria co-infected patients on EFV-based ART, an extension of the duration of AL treatment to five days using the current dose is proposed.

Liver involvement in hereditary hemorrhagic telangiectasia: can breath test unmask impaired hepatic first-pass effect?

Hepatic arteriovenous malformations (HAVMs) in hereditary hemorrhagic telangiectasia (HHT) have long been considered to have scarce clinical significance in most cases. Nevertheless, data are lacking regarding the influence of HAVMs on the liver first-pass effect on drugs in HHT patients. To gain insight into the effect of HAVMs on hepatic drug clearance by means of two specific (13)C-labeled probes, namely the (13)C-methacetin and (13)C-aminopyrine, 46 HHT patients and 44-matched healthy controls were enrolled. The liver first-pass effect was studied by the (13)C-based breath test using methacetin and aminopyrine. The methacetin breath test showed statistically significant reduced metabolism rates (p < 0.0001) in HHT when compared with controls, both in patients with and without CT-detectable HAVMs, and when expressed both as cumulative (13)C-percentage dose per hour and as (13)C-percentage peak after 15 min. In contrast, no significant difference was found between HHT and controls regarding aminopyrin metabolism rates. In HHT, (13)C%-methacetin breath test values are significantly lower than those found in normal subjects, probably due to the effect of hepatic shunts. A reduced perfusion and an impaired hepatic metabolism might affect hepatic drug clearance in HHT. Therefore, an appropriate dosage adjustments should be considered when high-hepatic-metabolism drugs are administered to HHT patients.

Inhibition of oral midazolam clearance by boosting doses of ritonavir, and by 4,4-dimethyl-benziso-(2H)-selenazine (ALT-2074), an experimental catalytic mimic of glutathione oxidase

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

* The viral protease inhibitor ritonavir is known to inhibit clearance of intravenous midazolam. * ALT-2074, a catalytic mimic of glutathione oxidase, inhibits human cytochrome P450 3A (CYP3A) isoforms in vitro.

WHAT THIS STUDY ADDS

* Short-term administration of low-dose ritonavir increases area under the plasma concentration curve following oral midazolam by a factor of 28. * Therefore ritonavir is an appropriate positive control inhibitor for clinical drug interaction studies involving CYP3A substrates. * Midazolam clearance is weakly inhibited by ALT-2074, consistent with its in vitro profile.

AIMS

We evaluated whether 'boosting' doses of ritonavir can serve as a positive control inhibitor for pharmacokinetic drug-drug interaction studies involving cytochrome P450 3A (CYP3A). The study also determined whether 4,4-dimethyl-benziso-(2H)-selenazine (ALT-2074), an investigational organoselenium compound that acts as a catalytic mimic of glutathione oxidase, inhibits CYP3A metabolism in vivo.

METHODS

Thirteen healthy volunteers received single 3-mg oral doses of midazolam on three occasions: in the control condition, during co-treatment with low-dose ritonavir (three oral doses of 100 mg over 24 h), and during co-treatment with ALT-2074 (three oral doses of 80 mg over 24 h).

RESULTS

Ritonavir increased mean (+/-SE) total area under the curve (AUC) for midazolam by a factor of 28.4 +/- 4.2 (P < 0.001), and reduced oral clearance to 4.2 +/- 0.5% of control (P < 0.001). In contrast, ALT-2074 increased midazolam AUC by 1.25 +/- 0.11 (P < 0.05), and reduced oral clearance to 88 +/- 8% of control.

CONCLUSIONS

Low-dose ritonavir produces extensive CYP3A inhibition exceeding that of ketoconazole (typically 10- to 15-fold midazolam AUC enhancement), and is a suitable positive control index inhibitor for drug-drug interaction studies. ALT-2074 inhibits CYP3A metabolism to a small degree that is of uncertain clinical importance.

Gefitinib-phenytoin interaction is not correlated with the C-erythromycin breath test in healthy male volunteers

AIMS

We aimed to describe the pharmacokinetic interaction between phenytoin, a potent CYP3A4 and P-glycoprotein (P-gp) (ABCB1) inducer, and gefitinib, a CYP3A4, CYP2D6 and P-gp substrate.

METHODS

An open-label, randomized, two-phase crossover study was conducted. Eighteen healthy male volunteers (nine homozygous CC and nine homozygous TT as determined by their ABCB1 C3435T polymorphism in exon 26) received a single oral dose of 250 mg gefitinib alone or after 5 days treatment with phenytoin (5 mg kg(-1) daily). Gefitinib plasma concentrations were determined by high-performance liquid chromatography. Hepatic CYP3A4 activity was evaluated by the (14)C-erythromycin breath test (ERMBT) and the ABCB1 and CYP2D6 genetic polymorphisms were determined by the TaqMan allelic discrimination assay and long polymerase chain reaction, respectively.

RESULTS

Following treatment with phenytoin, mean gefitinib C(max) and AUC(0-infinity) decreased by 26 +/- 44% [95% confidence interval (CI) for the difference 5-48%, P= 0.005] and 47 +/- 26% (95% CI for the difference 34-60%, P= 0.001), respectively, and apparent oral clearance increased by 126 +/- 93% (95% CI for the difference 80-172%, P= 0.004). Concomitantly, phenytoin increased the mean ERMBT by 91 +/- 44% (95% CI 75-105%, P < 0.001) from baseline, but the extent of liver CYP3A4 induction was not correlated to the extent of interaction. Furthermore, this interaction was independent of ABCB1 genetic polymorphism. The CYP2D6 genotype was slightly but significantly related to gefitinib clearance (P= 0.04) during the control phase.

CONCLUSIONS

The significant interaction between gefitinib and phenytoin was not correlated with the erythromycin breath test and was independent of ABCB1 polymorphism, but may involve presystemic CYP3A-mediated intestinal first-pass.

Maraviroc: Pharmacokinetics and drug Interactions

Maraviroc is a potent selective CCR5 antagonist and is the first of this new class of oral agents to be approved for the treatment of CCR5-tropic HIV type-1. Maraviroc is extensively metabolized by CYP3A4, with renal clearance accounting for approximately 23% of total clearance. The half-life of maraviroc is approximately 16 h. Maraviroc does not inhibit any of the major CYP450 enzymes at clinically relevant doses and it has not shown any clinically relevant effects on plasma concentrations of other agents; hence, no dose adjustments of coadministered agents are required. Maraviroc exposure is altered by agents that modulate the activity of CYP3A4 and, in some circumstances, maraviroc dose adjustment is necessary. This article aims to review all pharmacokinetic and drug interaction data available for maraviroc, and to provide a comprehensive summary of the dose adjustment recommendations for maraviroc when coadministered with agents from all classes of antiretroviral therapy as well as other commonly coadministered agents.

Pharmacologic consideration for the use of antiretroviral agents in the elderly

The prevalence of human immunodeficiency virus (HIV) infection among people older than 50 years is increasing. HIV-infected patients require lifelong treatment with antiretroviral agents to suppress viral replication and maintain immune function. The use of antiretroviral agents in the elderly can be complicated by multiple chronic comorbidities and coadministered non-HIV medications. The pharmacokinetics of antiretroviral agents may be altered due to age-related decrements in hepatic and renal function. The elderly may be more sensitive than younger people to antiretroviral drug toxicity. A better understanding of the pharmacokinetics of antiretroviral agents in the elderly is of importance for the successful management of complex antiretroviral regimens in this population.

Mini-series: I. Basic science. Uncertainty and inaccuracy of predicting CYP-mediated in vivo drug interactions in the ICU from in vitro models: focus on CYP3A4

Drug-drug interactions (DDIs) contribute significantly to the incidence of adverse drug reactions. Important advances in the knowledge of human drug-metabolizing enzymes have fueled the integration of in vitro drug metabolism and clinical DDIs studies for use in drug development programs and in the clinical setting. The activity of cytochrome P450 (CYP) 3A4 and P-glycoprotein are critical determinant of drug clearance, interindividual variability in drug disposition and clinical efficacy, and appears to be involved in the mechanism of numerous clinically relevant DDIs. Cell-based in vitro models are being increasingly applied in elucidating the pharmacokinetic profile of drug candidates during the preclinical steps of drug development. Human liver, intestinal samples and recombinant human CYP3A4 are now readily available as in vitro screening tools to predict the potential for in vivo DDIs. Although it is easy to determine in vitro metabolic DDIs, the interpretation and extrapolation of in vitro interaction data to in vivo situations requires a good understanding of pharmacokinetic principles. Clinicians and pharmacokineticists should recognize that in vitro models may not be clinically relevant in all situations. In the current article, research will be presented on drug metabolism and DDIs along with examples illustrating the utility of specific in vitro or in vivo approaches. In addition, the impact and clinical relevance of complexities such as dosing-route dependent effects, multi-site kinetics of drug-metabolizing enzymes and non-CYP determinants of metabolic clearance will be addressed.

A novel probe drug interaction study to investigate the effect of selected antiretroviral combinations on the pharmacokinetics of a single oral dose of maraviroc in HIV-positive subjects

AIMS

Maraviroc (UK-427 857), an antagonist of the CCR5 receptor with potent anti-HIV activity, was recently approved for use in treatment-experienced patients infected with CCR5-tropic HIV-1. The aim of this study was to evaluate the effect of selected commonly used antiretroviral therapy (ART) combinations on the pharmacokinetics of a single oral dose of maraviroc 300 mg in HIV-positive subjects compared with historical controls.

METHODS

In this study, four cohorts of HIV-positive patients (n = 8 each) receiving one of the following combination therapies were recruited: cohort 1--efavirenz + Combivir (lamivudine/zidovudine); cohort 2--efavirenz + didanosine + tenofovir; cohort 3--nevirapine + lamivudine + tenofovir; cohort 4--Kaletra (lopinavir/ritonavir) + stavudine + lamivudine. Subjects continued on their prescribed ART and also received a single oral dose of maraviroc 300 mg. Serial blood samples and urine for determination of maraviroc pharmacokinetics were collected over 12 h postdose. Plasma pharmacokinetic parameters from this study were compared with historical data generated in HIV-positive subjects receiving maraviroc monotherapy in a Phase IIa study.

RESULTS

A total of 29 subjects were recruited (eight each in cohorts 1-3, and five in cohort 4). The geometric mean ratios for AUC(12) and C(max) for each treatment group compared with maraviroc monotherapy were: 47% and 67% (cohort 1); 48% and 76% (cohort 2); 101% and 154% (cohort 3); and 265% and 180% (cohort 4), respectively. T(max) was similar in all treatment groups. Mean values for renal clearance ranged from 8.2 l h(-1) (cohort 1) to 13.2 l h(-1) (cohort 4). There were no renal clearance data collected in the comparator study.

CONCLUSIONS

The results of this study support those previously seen in healthy volunteer studies that showed that efavirenz reduces maraviroc exposure, whereas lopinavir/ritonavir increases maraviroc exposure. These data also suggest that nevirapine does not lead to a clinically significant effect on maraviroc pharmacokinetics.

Induction of P-glycoprotein expression and activity by ritonavir in bovine brain microvessel endothelial cells

Extended treatment with human immunodeficiency virus (HIV) protease inhibitors (HPIs) is standard in HIV/AIDS therapy. While these drugs have helped decrease the overall incidence of AIDS defining illnesses, the relative prevalence of HIV/AIDS dementia has increased. HPIs may cause induction of blood-brain barrier (BBB) drug transporters (P-glycoprotein; P-gp) and thereby limit entry of HPIs into brain tissue, increasing the probability that the brain could become an HIV sanctuary site. Using bovine brain microvessel endothelial cells (BMEC) as an in-vitro model of the BBB, the potential for the HIV protease inhibitor ritonavir to cause induction of P-gp activity and expression was examined. BMEC were isolated from fresh cow brain by enzymatic digest and density centrifugation. Primary culture BMEC were co-incubated with ritonavir or vehicle control for 120 h. Quantitative drug accumulation of rhodamine 123 (Rh123) and fluorescence microscopy were used as measures of P-gp activity. P-gp expression was assessed using quantitative Western blotting. Ritonavir decreased Rh123 cell accumulation and increased P-gp immunoreactive protein in a concentration-dependent manner. Fluorescent microscopy mirrored Rh123 quantitative studies. In BMEC pretreated with 30 microM ritonavir, Rh123 accumulation was decreased 40% and immunoreactive P-gp protein increased 2-fold. Collectively, a strong correlation between decreased Rh123 BMEC accumulation and increased P-gp immunoreactive protein was observed (Spearman r2 = 0.77, P < 0.0001). Thus extended exposure of BMEC to ritonavir caused a concentration-dependent increase in P-gp activity and expression. Similar findings may occur at the clinical level with prolonged HIV protease inhibitor use, giving insight into the central nervous system as an HIV sanctuary site and eventual development of HIV dementia.