Racivir

Racivir is an experimental anti-HIV drug that belongs to the class of drugs known as nucleoside reverse transcriptase inhibitors (NRTIs). These drugs interfere with the process of viral replication within cells to reduce the amount of HIV in the blood.

Racivir (RCV) is a cytosine analogue, closely related in structure to emtricitabine (Emtriva) and similarly active against hepatitis B. It has been proposed as an agent that will be active against hepatitis B resistant to 3TC (Epivir). Racivir is also closely related to D-D4FC, another NRTI being developed by Pharmasset Pharmaceuticals.

In animal studies, it was active against HIV-1 and hepatitis B. Racivir was effective in reducing viral load in patients who had the M184V and less than three thymidine analog mutations. It was thought that the drug might be positioned as second-line therapy in patients resistant to 3TC. It was effective in phase I and II clinical trials amongst treatment-experienced patients, when given with d4T and efavirenz. Plans for phase II/III clinical trials have not yet moved forward and Pharmasset is now seeking to license the drug to a development partner.

In a phase I/II dosing and efficacy study, racivir (RCV) was administered at three doses (200, 400, or 600mg once daily) in combination with d4T (stavudine, Zerit) and efavirenz (Sustiva). Six HIV-positive individuals were recruited to each dosing group. After day 15, treatment was discontinued and viral load continued to be monitored until day 35. Viral load had declined by an average of 2.02 to 2.42 log10 by day 14, and remained more than 2 log10 below baseline at day 28 at all doses. Rebound above this level began to be detected by day 35, but viral load still remained more than 1 log10 below baseline at this point.1

In a phase II study presented in 2007, racivir demonstrated good effectiveness and safety in treatment-experienced patients with the M184V mutation (associated with high-level resistance to 3TC) and fewer than three thymidine analogue mutations (TAMS).2

References

  1. Otto MJ et al. Sustained anti-HIV-1 effect of racivir combined with d4T and Sustiva following a 14-day treatment of infected volunteers. Tenth Conference on Retroviruses and Opportunistic Infections, Boston, abstract P552, 2003
  2. Cahn P et al. Racivir demonstrates safety and efficacy in patients harboring HIV with the M184V mutation and < 3 TAM. Fourteenth Conference on Retroviruses and Opportunistic Infections, Los Angeles, abstract 488, 2007b
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