Interindividual variability in the effect of atazanavir and saquinavir on the expression of lymphocyte P-glycoprotein.

OBJECTIVES: ABCB1 encodes the efflux transporter P-glycoprotein (P-gp), which regulates the intracellular concentration of many xenobiotics, including several HIV protease inhibitors (PIs). Exposure to some xenobiotics, such as the antibiotic rifampicin, increases P-gp expression. In the present study, we investigated the effect of the HIV PIs saquinavir and atazanavir on the expression and function of ABCB1 and P-gp in primary and cultured lymphocytes, as well as the molecular interactions between these drugs and P-gp. ABCB1 and P-gp expression and function were examined in lymphocyte samples from healthy subjects before and after atazanavir-boosted saquinavir treatment. Expression and function were also studied in CEM cells following exposure to atazanavir and saquinavir. The inhibitory effects of these drugs were investigated in ABCB1-transfected HEK293T cells. METHODS: P-gp expression and function were measured by flow cytometry. ABCB1 mRNA expression was evaluated using quantitative RT-PCR. RESULTS: There were no overall changes in ABCB1 or P-gp expression or function after saquinavir-atazanavir treatment in primary lymphocyte samples. However, there was considerable interindividual variability in baseline lymphocyte ABCB1 expression, as well as in the degree of change in ABCB1 expression after saquinavir-atazanavir administration. In cell culture, 5 microM saquinavir increased ABCB1 levels, although it did not affect P-gp expression. Atazanavir inhibited P-gp function at concentrations above therapeutic levels. CONCLUSIONS: Differences in lymphocyte ABCB1 expression, which may be caused by genetic polymorphisms in ABCB1 or its regulatory partners, are a likely cause of interindividual variation in the disposition and efficacy of clinically relevant P-gp substrates, including HIV PIs.

Pharmacokinetics of saquinavir with atazanavir or low-dose ritonavir administered once daily (ASPIRE I) or twice daily (ASPIRE II) in seronegative volunteers.

ASPIRE I and II were prospective, 3-way sequential crossover studies in healthy volunteers to compare the safety and pharmacokinetics of saquinavir/ritonavir (SQV/RTV) with saquinavir/atazanavir (SQV/ATV) administered either once daily (QD, ASPIRE I) or twice daily (BID, ASPIRE II). Treatments were separated by 10 days, and pharmacokinetic analyses were performed on days 11, 32, and 53. SQV pharmacokinetics were significantly higher when dosed with RTV compared to ATV (P < .05 for all comparisons). ATV pharmacokinetics were similar within treatment arms. ATV Cmin increased approximately 60%, and Cmax decreased approximately 35% with BID dosing compared with QD dosing. Women had higher exposure for all 3 protease inhibitors (PIs) compared with men after adjusting for weight. Adverse effects were primarily gastrointestinal-related with SQV/RTV and hyperbilirubinemia with SQV/ATV. Although SQV plasma concentrations were higher when coadministered with RTV, a combination of SQV/ATV administered BID may be a viable alternative in HIV-infected, PI-naive subjects intolerant to RTV.

Disease progression in HIV-infected patients treated with stavudine vs. zidovudine.

BACKGROUND AND OBJECTIVES: This prospective, observational study compared disease progression and death in HIV-1 patients treated with stavudine vs. zidovudine in the Collaborations in HIV Outcomes Research/U.S. (CHORUS) cohort. METHODS: Patients with a first occurrence of CD4 count <500 cells/microL (n=3301) were grouped as: no nucleoside reverse transcriptase inhibitor (NRTI) use; other NRTI without stavudine or zidovudine; stavudine with no zidovudine, with or without other NRTIs; and zidovudine with no stavudine, with or without other NRTIs. The risk for death or disease progression was evaluated in unadjusted analyses and using a Cox proportional hazards model, adjusting for: study site, age, gender, race, route of HIV infection, previous AIDS-defining conditions, number of previous antiretroviral regiments, CD4 count, HIV-1 RNA, and treatment variables. Sensitivity analyses were conducted to determine the sensitivity of the results to major modeling assumptions. A landmark analysis was conducted to determine the absolute difference in time to event. RESULTS: During a median follow-up of 2.4 years, there were 57 deaths and 348 AIDS-defining conditions in 405 patients. Stavudine treatment compared with zidovudine resulted in a greater percentage of patients with AIDS-defining events (14.5 vs. 10.9%; P=.013), and an increased risk of disease progression (HR=1.30; 95% CI: 1.01,1.7; P=.04). This result was not sensitive to modeling assumptions. Landmark analysis demonstrated an absolute difference in time to 95% event-free survival of 2.7 months for those with a CD4< or =200 cells/microL and 11 months for those 6 months after model entry. CONCLUSIONS: In unadjusted and adjusted analyses of 3301 HIV-1 infected patients, stavudine containing combination therapy was associated with an increased risk of disease progression or death compared to therapy containing zidovudine. Most of the difference was attributable to new cases of wasting.

Tenofovir disoproxil fumarate in nucleoside-resistant HIV-1 infection: a randomized trial.

BACKGROUND: Resistance to antiretroviral agents remains a leading cause of treatment failure for patients infected with HIV-1. OBJECTIVE: To describe the efficacy and safety of tenofovir disoproxil fumarate (tenofovir DF) compared with placebo in patients with detectable viral replication despite current antiretroviral therapy. DESIGN: Randomized, double-blind, placebo-controlled study through 24 weeks. After 24 weeks, all patients received open-label tenofovir DF for the remainder of the 48-week study. SETTING: 75 North American, European, and Australian HIV clinics. PATIENTS: 552 HIV-1-infected adults who were receiving antiretroviral therapy and had stable HIV-1 RNA levels ranging from 400 to 10,000 copies/mL. MEASUREMENTS: Change in HIV-1 RNA level (time-weighted average from baseline through week 24); proportion of patients with grade 3 or 4 laboratory abnormalities and adverse events; and genotypic HIV-1 resistance testing in a separate substudy at baseline, week 24, and week 48. RESULTS: A statistically significant decrease in HIV-1 RNA level through week 24 (the primary end point) was observed in the tenofovir DF group versus the placebo group (-0.61 log10 copies/mL vs. -0.03 log10 copies/mL, respectively [P < 0.001]; difference, -0.58 log10 copies/mL [95% CI, -0.68 to -0.49 log10 copies/mL]). In a virologic substudy, 94% of 253 patients had plasma isolates expressing reverse transcriptase mutations associated with nucleoside resistance mutations at baseline. Through week 24, the incidence of clinical adverse events was similar between patients receiving placebo and those receiving tenofovir DF (14% vs. 13%). No evidence of tenofovir DF-related toxicity was seen through week 48. CONCLUSION: In treatment-experienced patients with suboptimal viral suppression, tenofovir DF significantly reduced HIV-1 RNA level and had a safety profile similar to that of placebo.

The role of pharmacological enhancement in protease inhibitor-based highly active antiretroviral therapy.

Having changed the landscape in the treatment of HIV infection, the functional efficacy of current protease inhibitors (PIs) remains limited by their pharmacokinetic and pharmacodynamic profiles. Complex metabolism by the cytochrome P450 system (particularly the 3A4 isoenzyme), action of membrane drug transporter elements (such as P-glycoprotein and multi-drug resistance-associated proteins) and activation of the nuclear receptor steroid xenobiotic receptor may alter exposures and compromise the antiretroviral activity of these drugs. These factors, as well as inadequate adherence, can facilitate the emergence of PI resistance and lead to regimen failure. Coadministration of ritonavir can enhance exposures of a primary PI by inhibiting CYP3A4 metabolism, P-glycoprotein activity and multi-drug resistance protein-1-mediated efflux. Adding ritonavir, however, is not without cost. Dyslipidaemia (possibly increasing the risk of cardiovascular events), gastrointestinal intolerance, multiple drug-to-drug interactions and activation of steroid xenobiotic receptor can all result and must be balanced against the pharmacokinetic improvement rendered by the addition of ritonavir. Understanding the pharmacological origins for the variations in exposures of PIs, both between and within patients, is important for the successful use of these agents.

Young HIV-infected adults are at greater risk for medication nonadherence.

This study sought to estimate rates of adherence to nucleoside reverse transcriptase inhibitors (NRTIs) during the first year of administration in the California Medicaid (Medi-Cal) population. A retrospective analysis of pharmacy claims data regarding NRTI prescription refills was employed to estimate adherence and persistence with therapy throughout 1 year in treatment-naive individuals. Adherence was defined as the proportion of days on which drugs were taken during the first 365 days of therapy, and persistence was assessed according to whether prescriptions were refilled over time within a tolerable threshold (60 days). A total of 2614 men and 1174 women exhibited a mean overall adherence rate of 53.0%, and 35.6% of individuals were persistent with therapy throughout the year. No differences in persistence or adherence rates by sex were detected (P =.30). The proportion of individuals with adherence of 80% or better was 26%. Age was found to be significant in adherence and persistence by chi-square examination (P =.001). We conclude that nonadherence can be a critical issue during the first year following initiation of therapy. Comprehensive adherence support programs may be required to maximize adherence, especially among subjects aged 18-24 years, and should be made available early in the course of therapy, or before it is initiated.