Virological efficacy of 24-week fozivudine-based regimen in ART-naive patients from Tanzania and Côte d'Ivoire

Objective: Use of zidovudine (ZDV) in antiretroviral therapy is limited by toxicity and twice daily (b.i.d.) dosing. Fozivudine (FZD) is a ZDV prodrug, which is activated intracellularly to ZDV-monophosphate especially in mononuclear cells but not in bone marrow cells. FZD promises improved myelotoxicity and once daily (o.d.) dosing. Design: Randomized clinical trial. Methods: We conducted an open-label, phase II, proof-of-concept trial investigating three different FZD doses (800mg o.d., 600mg b.i.d., 1200mg o.d.) versus ZDV (300mg b.i.d.) in combination with lamivudine and efavirenz in HIV-infected, ARTnaive patients from Tanzania and Côte d'Ivoire. The primary objective was to demonstrate virological efficacy after 24 weeks in intent-to treat and per-protocol analysis. Secondary endpoints included safety and pharmacokinetic outcomes. Results: Of 119 participants included in the intent-to treat analysis, HIV RNA less than 50 copies/ml at 24 weeks was observed in 64 of 88 (73%) patients in the combined FZD arms versus 24 of 31 (77%) in the ZDV arm (RR 0.94, 95% confidence interval 0.75- 1.18). In the per-protocol analysis, responses were 64 of 77 (87%) versus 23 of 29 (79%), respectively (RR 1.09, 95% confidence interval 0.89-1.34). Outcomes were similar between FZD arms. Overall, treatments were well tolerated. Severe or worse anaemia occurred in two cases (one related to FZD, one to ZDV), grade III/IV neutropenia was less frequent in FZD compared with ZDV arms (22 versus 42%, P=0.035). Pharmacokinetic analysis supported o.d. administration of FZD. Conclusion: Virological 24-week efficacy was demonstrated in b.i.d. and o.d. administered FZD-based regimens. Reduced myelotoxicity of FZD needs to be confirmed in a larger trial.