Enfuvirtide: first fusion inhibitor for treatment of HIV infection.

PURPOSE: The mechanism of action, pharmacokinetics, clinical efficacy, adverse effects, and availability of enfuvirtide are discussed. SUMMARY: To date, 20 antiretrovirals have been approved by FDA for the treatment of HIV infection. The recent approval of enfuvirtide offers a new and fourth class of antiretroviral agents called fusion inhibitors. Enfuvirtide is indicated for use in treatment-experienced patients who have evidence of viral replication despite receiving current therapy. The drug is a 36-amino-acid synthetic peptide that prevents completion of the HIV fusion sequence. Absolute bioavailability after subcutaneous injection is 84%. Clinical trials indicate that adding enfuvirtide to a salvage regimen in heavily treated patients may lead to an improved virologic response. Up to a 1.48 log decrease in the viral load was seen at 48 weeks when enfuvirtide was combined with an optimized background regimen. Patients who have at least two or more active drugs in the regimen, a CD4+ cell count of >100 cells/mm3, and previous exposure to two or more antiretrovirals prior to starting enfuvirtide appear to respond best. The most common adverse effect, occurring in 98% of all enfuvirtide recipients, is an injection-site reaction that generally can be managed nonpharmacologically. A much less common but more significant concern is an increased risk of bacterial pneumonia. Enfuvirtide is available through the Fuzeon Progressive Distribution Program. The annual cost of therapy is about 24,000 dollars. CONCLUSION: Enfuvirtide is the first fusion inhibitor available for the treatment of HIV infection. The drug is indicated for use with other antiretroviral agents in treatment-experienced patients who have evidence of HIV replication despite ongoing antiretroviral treatment.