A 42-Week Open-Label Study to Assess the Pharmacokinetics, Antiretroviral Activity, and Safety of Amprenavir or Amprenavir plus Ritonavir in Combination with Abacavir and Lamivudine for Treatment of HIV-Infected Patients

Quantification of human hepatocyte cytochrome P450 enzymes and transporters induced by HIV protease inhibitors using newly validated LC-MS/MS cocktail assays and RT-PCR

Human immunodeficiency virus (HIV) protease inhibitors (PIs) produce profound and unpredictable drug-drug interactions (DDIs) that cannot be explained fully by their inhibition/inactivation of CYP3A enzymes. Delineating and quantifying the CYPs and transporters inducible by PIs are crucial in developing an integrative mechanistic understanding and prediction of PI-based DDIs. To do so, two LC-MS/MS cocktail assays were modified and validated simultaneously to quantify the CYP activity of CYP3A, 2B6, 2C8, 2C9, 2C19, 1A, 2E1, 2A6 and 2D6 enzymes. These new assays were applied to evaluate the induction potential of eight PIs in microsomes isolated from PI-treated human hepatocytes. The mRNA expression of these CYPs and transporters (OATP1B1, OATP1B3, OATP1A2, MDR1, MRP2 and MRP4) was also evaluated using relative RT-PCR. The majority of PIs were net inducers of CYP3As and 2B6 at both the mRNA and activity level (> 2-fold), while ritonavir, saquinavir, nelfinavir or lopinavir did not induce CYP3A activity (< 2-fold), presumably due to CYP3A inactivation. OATP1B1 and MDR1 were the only two hepatic transporters induced (> 2-fold) by the PIs. Amprenavir was the most potent net inducer. In conclusion, our validated cocktail assays can be implemented to comprehensively quantify CYP activities in human liver microsomes and hepatocyte studies. The results also provide the much needed data on the net induction potential of the PIs for hepatic CYPs and transporters. A qualitative agreement was observed between our results and published PI-based DDIs, suggesting that human hepatocytes are a useful platform for more extensive and quantitative in vitro-in vivo prediction of PI-based DDIs.

Rate of virologic failure and selection of drug resistance mutations using different triple nucleos(t)ide analogue combinations in HIV-infected patients

Virologic failure seems to occur more frequently in HIV-infected patients treated with triple nucleoside analogue (NA) combinations than with regimens including nonnucleoside reverse transcriptase inhibitors or protease inhibitors. However, the rate of failure and resistance profiles may differ with distinct triple NA combinations. A retrospective review of all HIV-infected individuals who received triple NA combinations at our institution was conducted. Virologic failure was defined as lack of achievement of plasma HIV-RNA<50 copies/ml at week 16 following initiation of antiretroviral therapy or as viral rebound in subjects with prior undetectable viremia. Genotypic analyses were performed at the time of first virological failure. Of the 261 patients identified, 13 were drug naive, 126 had underwent simplification, and 122 were antiretroviral-experienced patients with detectable viral load. Virologic failure was recorded in 95 (36.4%) after an average follow-up of 19 months. Rates were 0.67 in drug-naive, 0.55 in simplification, and 2.38 in rescue interventions for 100 persons-month follow-up. Factors associated with virologic failure in the multivariate Cox regression analysis were rescue vs naive or simplification strategies (OR 2.6; 95% CI 1.6-4.2) and using tenofovir as part of the combination (OR 2.04; 95% CI 1.3-3.2). In contrast, the use of AZT prevented virologic failure (OR 0.52; 95% CI 0.3-0.8). M184V was the most frequent resistance mutation (75.4%), followed by T215Y (52.5%) and K65R (14.8%). Of note, K65R did not develop in patients taking AZT nor in those with prior thymidine-associated mutations (TAMs). Conversely, subjects who developed K65R did not accumulate TAMs. Virologic failure is relatively frequent in patients treated only with triple NA regimens, particularly in the setting of rescue therapy. The use of TDF might be associated with a higher risk of virologic failure and, conversely, AZT might be protective. The presence of TAMs precluded the selection of K65R in patients treated with TDF. Resistance pathways for TDF and thymidine analogues seem to be divergent and could be the basis to explore a synergism between these drugs.

Plasma amprenavir pharmacokinetics and tolerability following administration of 1,400 milligrams of fosamprenavir once daily in combination with either 100 or 200 milligrams of ritonavir in healthy volunteers

Once-daily (QD) fosamprenavir (FPV) at 1,400 mg boosted with low-dose ritonavir (RTV) at 200 mg is effective when it is used in combination regimens for the initial treatment of human immunodeficiency virus infection. Whether a lower RTV boosting dose (i.e., 100 mg QD) could ensure sufficient amprenavir (APV) concentrations with improved safety/tolerability is unknown. This randomized, two 14-day-period, crossover pharmacokinetic study compared the steady-state plasma APV concentrations, safety, and tolerability of FPV at 1,400 mg QD boosted with either 100 mg or 200 mg of RTV QD in 36 healthy volunteers. Geometric least-square (GLS) mean ratios and the associated 90% confidence intervals (CIs) were estimated for plasma APV maximum plasma concentrations (Cmax), the area under the plasma concentration-time curve over the dosing period (AUC0-tau), and trough concentrations (Ctau) during each dosing period. Equivalence between regimens (90% CIs of GLS mean ratios, 0.80 to 1.25) was observed for the plasma APV AUC0-tau (GLS mean ratio, 0.90 [90% CI, 0.84 to 0.96]) and Cmax (0.97 [90% CI, 0.91 to 1.04]). The APV Ctau was 38% lower with RTV at 100 mg QD than with RTV at 200 mg QD (GLS mean ratio, 0.62 [90% CI, 0.55 to 0.69]) but remained sixfold higher than the protein-corrected 50% inhibitory concentration for wild-type virus, with the lowest APV Ctau observed during the 100-mg QD period being nearly threefold higher. The GLS mean APV Ctau was 2.5 times higher than the historical Ctau for unboosted FPV at 1,400 mg twice daily. Fewer clinical adverse drug events and smaller increases in triglyceride levels were observed with the RTV 100-mg QD regimen. Clinical trials evaluating the efficacy and safety of FPV at 1,400 mg QD boosted by RTV at 100 mg QD are now under way with antiretroviral therapy-naïve patients.

Ritonavir increases plasma amprenavir (APV) exposure to a similar extent when coadministered with either fosamprenavir or APV

To compare the effect of ritonavir on plasma amprenavir pharmacokinetics, healthy adults received either fosamprenavir (700 mg twice a day [BID]) or amprenavir (600 mg BID) alone and in combination with ritonavir (100 mg BID). Ritonavir increased plasma amprenavir pharmacokinetic parameters to a similar extent when coadministered with either fosamprenavir or amprenavir.

When to Initiate Highly Active Antiretroviral Therapy in Sub-Saharan Africa? A South African Cost-Effectiveness Study

Background

Large-scale programmes increasing access to highly active antiretroviral therapy (HAART) are being implemented in sub-Saharan Africa. However, cost-effectiveness of initiating treatment at different CD4 count thresholds has not been explored in resource-poor settings.

Methods

A cost-effectiveness analysis was conducted from a public health perspective using primary treatment outcomes, healthcare utilisation and cost data (Jan 2004 local prices; US$1=7.6 Rands) derived from the Cape Town AIDS Cohort. A Markov state-transition model was developed to estimate life-expectancy, lifetime costs, quality-adjusted life-years (QALYs), cost per life-year and QALY gained for initiating HAART at three CD4 cell count thresholds (<200/μl, 200–350/μl and >350/μl), including the no antiretroviral therapy (No-ART) alternative. Each treatment option was compared with the next most effective undominated option.

Results

Mean life-expectancy was 6.2, 18.8, 21.0 and 23.3 years; discounted (8%) QALYs were 3.1, 6.2, 6.7 and 7.4; and discounted lifetime costs were US$5,250, US$5,434, US$5,740, US$6,588 for No-ART, and therapy initiation at <200/μl, 200–350/μl and >350/μl scenarios respectively. Clinical benefits increased significantly with early therapy initiation. Initiating therapy at <200/μl had an incremental cost-effectiveness ratio (ICER) of US$54 per QALY versus No-ART, 200–350/μl had an ICER of US$616 versus therapy initiation at <200/μl, and >350/μl had an ICER of US$1,137 versus therapy initiation at 200–350/μl ICERs were sensitive to HAART cost.

Conclusions

HAART is reasonably cost-effective for HIV-infected patients in South Africa, and most effective if initiated when CD4 count >200/μl. Deferring treatment to <200/μl would reduce the aggregate cost of treatment, but this should be balanced against the significant clinical benefits associated with early therapy.

Once-daily antiretroviral therapy: Spanish Consensus Statement

BACKGROUND

Administration of antiretroviral therapy (ART) once daily is creating extraordinary interest among the members of the scientific community and also among those who receive the therapy. However, in clinical practice, some doubts remain about its use.

OBJECTIVES

This document examines the characteristics and possibilities of treatment administered once daily.

METHODS

Consensus of 248 Spanish experts in the field.

RESULTS

Once-daily dosing is considered an added value which could favour adherence and, therefore, efficacy, as well as the quality of life of certain patients, however, the objective of adequate adherence in the long term is often difficult to achieve regardless of the treatment used. In theory, any patient can receive once-daily therapy, although some patients could particularly benefit from it, e.g. those with unfavourable social or personal circumstances, including drug users, patients whose treatment must be supervised, patients receiving multiple medications, or those who need rescue therapy after multiple treatment failures. At present, it is possible to design once-daily ART using some of the combinations of drugs considered as first-choice in national and international recommendations for antiretroviral therapy, but the options are still limited. The marketing of new drugs with this characteristic could allow us to increase the number and types of patient who can benefit from once-daily regimens, including those patients who need rescue therapy.

CONCLUSIONS

Once-daily ART is a good alternative to regimens administered several times each day when a potent combination of active drugs is available.