Enfuvirtide (T-20; Fuzeon Trimeris/Roche), the first in a new class of HIV drugs known as fusion inhibitors, has received accelerated approval from the FDA for use with other antiretrovirals in adults and children with viral replication despite ongoing antiretroviral therapy. This review describes the mechanism of action and pharmacokinetics of the new drug, and outlines the results of the 2 clinical studies that led to its approval. Sections on adverse effects, development of resistance, and dosage and cost are also included. The review concludes with an overall assessment of the...