Enfuvirtide (INN), sold under the brand name Fuzeon, is an HIV fusion inhibitor, the first of a class of antiretroviral drugs used in combination therapy for the treatment of AIDS/HIV.

[2] Common adverse drug reactions (≥1% of patients) associated with enfuvirtide therapy include: injection site reactions (pain, hardening of skin, erythema, nodules, cysts, itch; experienced by nearly all patients, particularly in the first week), peripheral neuropathy, insomnia, depression, cough, dyspnoea, anorexia, arthralgia, infections (including bacterial pneumonia) and/or eosinophilia.

Various hypersensitivity reactions occur infrequently (0.1–1% of patients), symptoms of which include rash, fever, nausea, vomiting, chills, rigors, hypotension, elevated hepatic transaminases; and possibly more severe reactions including respiratory distress, glomerulonephritis and/or anaphylaxis – rechallenge is not recommended.

[5] Variable susceptibility to enfuvirtide has been observed in clinical isolates, with acquired resistance the result of a mutated 10 amino acid motif in viral gp41.

It was approved on the basis of two studies which compared the effect of optimized regimens of antiretroviral medication with and without the addition of enfuvirtide on serum viral load.