Novel clinical trial designs for the development of new antiretroviral agents

Design of HIV noninferiority trials: where are we going?

Since the introduction of zidovudine, a nucleoside analogue reverse transcriptase inhibitor, there has been continuous improvement in the efficacy of antiretroviral treatments. Briefly, antiretroviral therapy moved from the era of zidovudine monotherapy to a combination of two analogues of the reverse transcriptase and then to triple-drug therapy with the introduction of protease inhibitors in 1996. The efficacy of triple-drug combinations was further consolidated with the introduction of the non-nucleoside analogue reverse transcriptase inhibitor. Beyond 1996, the impressive improvement in efficacy has implied that death and clinical endpoints could not be reasonably used as primary efficacy endpoints. Recent studies used plasma viral load as surrogate endpoints to evaluate efficacy of antiretroviral combinations. Progress in antiretroviral efficacy has also led to a move from superiority to noninferiority design. Methodological issues in noninferiority design have been already criticized, but recent trials provide a good opportunity for discussing some key features of that design. Recent studies are used to illustrate some inconsistencies in the choice of response rates, power and noninferiority margin. It appears that HIV noninferiority trials are overpowered by assuming lower success rates than those observed, enrolling a large number of patients and choosing a large margin. Consequently, failure to demonstrate noninferiority is uncommon. Novel designs or endpoints should be introduced emphasizing the expected benefits in terms of toxicity, adherence, resistance or costs.

Vicriviroc plus optimized background therapy for treatment-experienced subjects with CCR5 HIV-1 infection: final results of two randomized phase III trials

BACKGROUND

Vicriviroc, a novel HIV CCR5 antagonist, demonstrated significant efficacy and favorable tolerability in phase II trials in treatment-experienced subjects, supporting further evaluation in phase III studies.

METHODS

Two identical double-blind, placebo (PBO)-controlled trials in CCR5-tropic HIV-infected subjects with documented resistance to two antiretroviral classes were conducted. Subjects were randomized to vicriviroc 30 mg QD (N = 571) or PBO (N = 286) with open-label optimized background therapy (OBT) containing ≥2 fully active antiretroviral drugs. The primary endpoint was percentage of subjects with <50 copies/mL HIV RNA at 48 weeks. It was analyzed in a logistic regression with treatment (vicriviroc + OBT/PBO + OBT), use of enfuvirtide in baseline OBT (yes/no), and baseline HIV RNA (≤100,000/>100,000 copies/mL) as covariates. In addition, a pre-planned analysis to examine other efficacy and safety endpoints was conducted.

RESULTS

Baseline characteristics of the pooled mITT population (vicriviroc, n = 486; PBO, n = 235) included mean HIV RNA of 4.6 log(10) copies/mL and mean CD4 count of 257 cells/μL. Approximately 60% of subjects received ≥3 active drugs in the OBT. The percentage of subjects with <50 copies/mL HIV RNA was not significantly different between vicriviroc and PBO at week 48 (64% vs 62%, p = 0.6). However, in subjects receiving ≤2 active drugs in their OBT, the proportion achieving <50 copies/mL HIV RNA was higher in those receiving vicriviroc compared with PBO (70% vs 55%, p = 0.02).

CONCLUSIONS

The studies failed to show significant efficacy gains when vicriviroc was added to OBT. However, given the efficacy results of earlier vicriviroc trials and other CCR5 antagonist, studies are needed to define the role of this class of drugs in the treatment of HIV. Clinical trial identifier: http://www.clinicaltrial.gov/: VICTOR-E3 (NCT00523211) and VICTOR-E4 (NCT00474370).