FP-21399 is being developed as an HIV fusion inhibitor. Developed by Lexigen (formerly Fuji ImmunoPharmaceutical), FP-21399 is designed to prevent HIV infection of cells after binding has occurred.

Early trials to assess pharmacokinetics and tolerability have been conducted. FP-21399 was administered as a single, one-hour infusion or as a one-hour infusion given once a week for four weeks. It was found to be well tolerated.

The most frequent adverse event was a change in urine colour and skin colour which occurred in more than half of participants. Thirteen people received FP-21399 over four weeks, of whom nine had CD4 cell count increases, two had viral load declines of more than 1 log₁₀, and two went from low to undetectable viral loads (Dezube 2000).

Key research

Dezube treated 34 HIV-infected people with FP-21399 with a single IV dose (0.9, 1.7, 2.8, 4.2mg/kg) or as a once weekly infusion (1, 2 and 3mg/kg) over 4 weeks. Half-life was 4 hours. Side-effects included discoloration of skin and urine. Of the patients who received 4 weeks of treatment, 9 had their CD4 cell count rise by more than 15%. Two had their viral loads fall by more than half a log with two others achieving undetectable viral load.

References

Dezube BJ et al. A fusion inhibitor (FP-21399) for the treatment of human immunodeficiency virus infection: a phase I study. J Infect Dis 182(2): 607-610, 2000.