Cytochrome P450 3A inhibition by atazanavir and ritonavir, but not demography or drug formulation, influences saquinavir population pharmacokinetics in human immunodeficiency virus type 1-infected adults

Intracellular Penetration of Atazanavir, Ritonavir and Dolutegravir With Concomitant Rifampicin: A Dose Escalation Study

Ritonavir-boosted atazanavir is a victim of drug-drug interaction with rifampicin, a key component of antitubercular treatment. In a recent dose escalation clinical trial, we showed that increasing atazanavir/ritonavir to 300/100 mg b.i.d. compensates for reduced drug exposure in plasma due to rifampicin, but the intracellular effects remained unexplored. This sub-study investigated the intracellular penetration of atazanavir/ritonavir and dolutegravir into peripheral blood mononuclear cells (PBMC). Twenty-six healthy volunteers living with HIV, virologically suppressed, and taking atazanavir/ritonavir containing regimens were enrolled. The trial consisted of four sequential periods: PK1, participants were on atazanavir/ritonavir 300/100 mg q.d.; at PK2, rifampicin 600 mg q.d. and dolutegravir 50 mg b.i.d. were added (2 weeks); at PK3, atazanavir/ritonavir dose was increased to 300/100 mg b.i.d. (1 week); at PK4, rifampicin dose was doubled (1 week). Atazanavir, ritonavir, and dolutegravir were quantified in plasma and PBMC using LC-MS/MS methods to evaluate steady-state concentrations at the end of each period. Atazanavir/ritonavir dose escalation successfully restored intracellular concentrations comparable to those observed without rifampicin, with a geometric mean ratio of 0.99 (CI90 0.72-1.41) for atazanavir at PK3 compared with PK1. The intracellular concentration of dolutegravir increased significantly with atazanavir/ritonavir dose escalation, similar to plasma. Finally, further, increasing the rifampicin dose did not show an additional impact on atazanavir/ritonavir concentrations in PBMC. The study confirms that increasing the ATV/r dose can be an effective strategy for compensating rifampicin effects even at the intracellular level, supporting its use in clinical settings.

Clinical use of cobicistat as a pharmacoenhancer of human immunodeficiency virus therapy

The pharmacoenhancement of plasma concentrations of protease inhibitors by coadministration of so-called boosters has been an integral part of antiretroviral therapy for human immunodeficiency virus (HIV) for 1.5 decades. Nearly all HIV protease inhibitors are combined with low-dose ritonavir or cobicistat, which are able to effectively inhibit the cytochrome-mediated metabolism of HIV protease inhibitors in the liver and thus enhance the plasma concentration and prolong the dosing interval of the antiretrovirally active combination partners. Therapies created in this way are clinically effective regimens, being convenient for patients and showing a high genetic barrier to viral resistance. In addition to ritonavir, which has been in use since 1996, cobicistat, a new pharmacoenhancer, has been approved and is widely used now. The outstanding property of cobicistat is its cytochrome P450 3A-selective inhibition of hepatic metabolism of antiretroviral drugs, in contrast with ritonavir, which not only inhibits but also induces a number of cytochrome P450 enzymes, UDP-glucuronosyltransferase, P-glycoprotein, and other cellular transporters. This article reviews the current literature, and compares the pharmacokinetics, pharmacodynamics, and safety of both pharmacoenhancers and discusses the clinical utility of cobicistat in up-to-date and future HIV therapy.

Clinical pharmacokinetics of antiretroviral drugs in older persons

INTRODUCTION

Combination antiretroviral therapy has enabled HIV-infected persons to reach older ages in high numbers. Hepatic and renal changes that normally occur with advancing age occur earlier and with higher incidence in HIV-infected individuals. A limited number of prospective controlled studies have demonstrated small reductions (17 to 41%) in lopinavir, atazanavir and lamivudine clearance in older versus younger adults. A much larger number of retrospective studies in adults (age range ∼ 20 to 60 years), including all antiretroviral drugs, have evaluated age as a covariate for pharmacokinetics. Most studies did not detect substantial associations between drug exposures and age.

AREAS COVERED

This review summarizes antiretroviral drug pharmacokinetics in older persons. The authors review articles from PubMed (search terms: elderly, antiretroviral, pharmacokinetics) in addition to the bibliographies of those selected.

EXPERT OPINION

The evidence to date does not support major pharmacokinetic changes in adults between ∼ 20 and 60 years of age. However, additional prospective, well-controlled studies are needed in more persons > 60 years, including those with frailty and comorbidities, with assessment of unbound drug clearance, and incorporation of adherence, pharmacogenetics and concomitant medications. Until then, guidelines for drug-drug interactions and dosing in renal and hepatic impairment should be followed in older HIV-infected individuals.

Chronic exposure to nicotine and saquinavir decreases endothelial Notch-4 expression and disrupts blood-brain barrier integrity

Since the advent of HAART, there have been substantial improvements in HIV patient survival; however, the prevalence of HIV associated dementia has increased. Importantly, HIV positive individuals who smoke progress to HIV associated neurological conditions faster than those who do not. Recent in vitro data have shown that pharmacological levels of saquinavir causes endothelial oxidative stress and significantly decreases Notch-4 expression, a primary protein involved in maintaining stability of blood-brain barrier (BBB) endothelium. This is concerning as nicotine can also generate reactive oxygen species in endothelium. It is largely unknown if pharmacological doses of these drugs can cause a similar in vivo down-regulation of Notch-4 and if there is a concurrent destabilization of the integrity of the BBB. The data herein show: (i) nicotine and protease inhibitors cause an additive oxidative stress burden in endothelium; (ii) that the integrity of the BBB is disrupted after concurrent chronic nicotine and protease inhibitor administration; and (iii) that BBB endothelial dysfunction is correlated with a decrease in Notch-4 and ZO-1 expression. Considering the high prevalence of smoking in the HIV infected population (3- to 4-fold higher than in the general population) this data must be followed up to determine if all protease inhibitors cause a similar BBB disruption or if there is a safer alternative. In addition, this data may suggest that the induced BBB disruption may allow foreign molecules to gain access to brain and be a contributing factor to the slow progression of HIV associated dementia.