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Unbound drug is the pharmacodynamically relevant concentration. This study aimed to determine if chronologic age or markers of biologic aging, such as the frailty phenotype and p16INK4a gene expression, altered unbound pharmacokinetics (PKs) of efavirenz (EFV) and atazanavir/ritonavir (ATV/RTV). Sixty human immunodeficiency virus (HIV)-infected participants receiving EFV and 31 receiving ATV/RTV provided 1 to 11 samples to quantify total and unbound plasma concentrations. Population PK models with total and unbound concentrations simultaneously described are developed for each drug. The unbound fractions for EFV, ATV, and RTV are 0.65%, 5.67%, and 0.63%, respectively. Covariate analysis suggests RTV unbound PK is sensitive to body size; unbound fraction of RTV is 34% lower with body mass index (BMI) above 30 kg/m2 . No alterations in drug clearance or unbound fraction with age, frailty, or p16INK4a expression were observed. Assessing functional and physiologic aging markers to inform potential PK changes is necessary to determine if drug/dosing changes are warranted in the aging population.

Drug-drug interactions between antiretroviral medications and rifampin complicate the treatment of HIV and tuberculosis coinfection. This study evaluated the effect of rifampin on the pharmacokinetics of oral cabotegravir, an integrase strand transfer inhibitor being investigated for long-acting treatment and prevention of HIV-1 infection. This was a phase I, single-center, open-label, fixed-sequence crossover study in healthy adults. The objective was to evaluate the effect of steady-state rifampin on the single-dose plasma pharmacokinetics of cabotegravir. Subjects received a single oral dose of cabotegravir (30 mg) on day 1 followed by plasma sampling on days 1 to 8. Treatment with once-daily oral rifampin (600 mg) occurred on days 8 to 28. Subjects received a second dose of 30 mg cabotegravir on day 21 followed by pharmacokinetic sampling on days 21 to 28. Fifteen subjects were enrolled and completed the study. Rifampin decreased the cabotegravir area under the concentration-time curve from 0 h to infinity and the half-life by 59% and 57%, respectively, whereas oral clearance was increased 2.4-fold. The maximum concentration of cabotegravir in plasma was unaffected by coadministration with rifampin. All adverse events were mild in severity, with chromaturia attributed to rifampin observed in all subjects. Rifampin induction of cabotegravir metabolism resulted in increased cabotegravir oral clearance and significantly decreased cabotegravir exposures. Rifampin is expected to increase cabotegravir clearance following long-acting injectable administration. Concomitant administration of rifampin with oral and long-acting formulations of cabotegravir is not recommended currently without further study. (This study has been registered at ClinicalTrials.gov under registration no. NCT02411435.)

Background Cabotegravir (CAB) is an integrase inhibitor in phase 3 clinical trials for the treatment and prevention of HIV. CAB undergoes hepatic metabolism primarily via UGT1A1; thus hepatic impairment has the potential to affect CAB exposure. Methods This was a multi-center, single-dose, open-label, parallel group study to evaluate the effect of moderate hepatic impairment on the pharmacokinetics (PK) and safety of CAB. Adults with moderate hepatic impairment as determined by Child-Pugh classification score of 7–9 (n = 8) and matched healthy control subjects (n = 8) were enrolled. Control subjects were matched for gender, age (±10 years), and body mass index (BMI) (±25%). Subjects received oral CAB 30 mg as a single dose in the fasted state followed by serial PK sampling for 168 hours. CAB unbound concentrations at 2 and 24 hours after dosing were determined by equilibrium dialysis. Non-compartmental PK analysis was performed; geometric least squares (GLS) mean ratios (hepatic impaired group/control group) and 90% confidence intervals (CI) were generated. Results Sixteen subjects completed study; 12 (75%) male, mean age 59 years (range: 51–67), mean BMI 29 kg/m2 (range: 21–37), and total Child Pugh score in range of 7–9. CAB PK parameters were similar between subjects with moderate hepatic impairment and matched healthy subjects. The GLS mean ratios (90% CI) for AUC(0-∞), Cmax, C24, CL/F, and t1/2 were 0.73 (0.50, 1.06), 0.69 (0.51, 0.93), 0.73 (0.53, 1.02), 1.38 (0.95, 2.01), and 0.82 (0.65, 1.04), respectively. Although highly protein bound, the unbound fraction of CAB was increased in subjects with moderate hepatic impairment relative to healthy subjects with GLS mean ratio (90%CI) of 2.14 (1.57, 2.90) at 2 hours post dose and 1.90 (1.14, 3.18) at 24 hours post dose; this was associated with lower serum albumin concentrations and was not considered clinically significant. All adverse events (AE) were reported as mild (Grade 1) to moderate (Grade 2) in severity and no serious AEs were reported. Conclusion Plasma exposures of CAB in subjects with moderate hepatic impairment were similar to those in healthy subjects. No dose adjustment of CAB is required for subjects with mild to moderate hepatic impairment. Disclosures J. S. Shaik, GlaxoSmithKline: Employee and Shareholder, Salary; S. Ford, PAREXEL International: Employee, Salary; Y. Lou, PAREXEL International: Employee, Salary; Z. Zhang, PAREXEL International: Employee, Salary; K. Bakshi, GlaxoSmithKline: Employee and Shareholder, Salary; A. Tenorio, ViiV Healthcare: Employee and Shareholder, Salary; C. Trezza, ViiV Healthcare: Employee and Shareholder, Salary; W. Spreen, ViiV Healthcare: Employee and Shareholder, Salary; P. Patel, ViiV Healthcare: Employee and Shareholder, Salary

The incidence of HIV remains alarmingly high in many parts of the world. Prophylactic use of antiretrovirals, capable of concentrating in the anatomical sites of transmission, may reduce the risk of infection after an unprotected sexual exposure. To date, orally and topically administered antiretrovirals have exhibited variable success in preventing HIV transmission in large-scale clinical trials. Antiretroviral mucosal pharmacokinetics may help explain the outcomes of these investigations. Penetration and accumulation of antiretrovirals into sites of transmission can influence dosing strategies and pre-exposure prophylaxis clinical trial design. Antiretroviral tissue distribution varies widely within and between drug classes, attributed in part to their physicochemical properties and tissue-specific drug transporter expression. Nucleoside (-tide) reverse transcriptase inhibitors, the CCR5 antagonist maraviroc, and the integrase inhibitor raltegravir demonstrate the highest penetration into the male and female reproductive tracts and colorectal tissue relative to blood. This review will describe antiretroviral exposure in anatomic sites of transmission, and place these findings in context with the prevention of HIV and the efficacy of pre-exposure prophylactic strategies.