Phase II placebo-controlled trial of fozivudine tidoxil for HIV infection: pharmacokinetics, tolerability, and efficacy

Fozivudine tidoxil (FZD) is a thioether lipid-zidovudine (ZDV) conjugate with anti-HIV activity demonstrated in vitro and in pilot phase I studies. To assess its safety, efficacy and pharmacokinetics, we conducted a multicenter, randomized, double-blind, placebo-controlled trial of FZD monotherapy in 72 HIV-infected patients who had not previously received antiretroviral therapy. In each dosage group (200 mg daily, 400 mg daily, 200 mg twice daily, 800 mg daily, 400 mg twice daily, and 600 mg twice daily), 12 patients were randomized to receive in a 10:2 ratio either FZD or a placebo for 4 weeks. Overall, FZD was well tolerated in all dosage groups; only 1 patient discontinued the drug, because of a moderate rise in aminotransaminase activity. HIV viral load fell in all the patients who were receiving FZD, except in the 200 mg daily group. The largest decrease (-0.67 log10) was observed in the 600 mg twice daily group. The plasma half-life was significantly longer (approximately 3.8 hours) than that of the parent drug ZDV. Exposure to ZDV, as reflected by the area under the time-concentration curve, was much lower after FZD than after ZDV administration. FZD thus appears to be as effective as and potentially better tolerated than ZDV during short-term administration and has the advantage of once daily intake.