Fosamprenavir: a review of its use in the management of antiretroviral therapy-naive patients with HIV infection.

Fosamprenavir (GW433908, Lexiva, Telzir) is an oral prodrug of the protease inhibitor (PI) amprenavir, with a reduced daily pill burden. Fosamprenavir, in combination with other antiretroviral agents, is indicated for the treatment of patients with HIV infection, particularly those who have not previously received antiretroviral therapy. Viral load reductions were at least as great with fosamprenavir-based regimens as those achieved with nelfinavir-based regimens in two large, 48-week, randomised, multicentre trials in antiretroviral therapy-naive patients with HIV infection. In the NEAT study, more patients receiving twice-daily fosamprenavir in combination with abacavir and lamivudine achieved HIV RNA levels <400 copies/mL than those receiving a similar nelfinavir-based regimen. Results of the SOLO study showed similar reductions in viral load among patients who received once-daily ritonavir-boosted fosamprenavir and those treated with twice-daily nelfinavir, both in combination with twice-daily abacavir and lamivudine. In both trials, virological failure rates were at least twice as high with the nelfinavir-based regimen as they were with the fosamprenavir-based regimen. Fosamprenavir was generally well tolerated in clinical trials. The most common adverse events among patients treated with fosamprenavir, with or without ritonavir, plus abacavir and lamivudine were diarrhoea, nausea, vomiting, abdominal pain, drug hypersensitivity and skin rash. The incidence of diarrhoea was significantly lower with fosamprenavir-based therapy than with nelfinavir-based therapy in the NEAT and SOLO trials. The resistance profile of fosamprenavir is consistent with that of amprenavir. Amprenavir-resistant viral isolates from patients experiencing treatment failure with fosamprenavir-based therapy in the NEAT study showed little or no cross-resistance to several other PIs, and protease mutations commonly selected for by various other PIs were not observed. In the SOLO study, protease resistance mutations were not observed in viral isolates from patients experiencing treatment failure with ritonavir-boosted fosamprenavir-based therapy. In conclusion, fosamprenavir-based regimens have shown good antiviral efficacy and are generally well tolerated in antiretroviral therapy-naive patients with HIV infection. Available data on the resistance profile of the drug suggest that it may be used early in the course of therapy without compromising a range of future treatment options. The relatively low pill burden and lack of food restrictions with fosamprenavir may improve adherence to therapy. Further studies are needed to compare fosamprenavir with other PIs and to establish the long-term efficacy of fosamprenavir-based regimens. In conclusion, fosamprenavir appears to be a promising agent for the treatment of antiretroviral therapy-naive patients with HIV infection.