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Infection & antiviral

Enfuvirtide

Also called Fuzeon, T-20, pentafuside

Enfuvirtide was the first HIV drug that blocks the virus from fusing with and entering cells. It is a twice-daily injection used only in people whose HIV keeps growing despite other medicines.

FDA-approvedApproved by the FDA for at least one use after large human trials.

All printable flashcards

Drawn from its published sequence: 36 residues, one bead each.

Overview

Enfuvirtide was the first HIV drug that blocks the virus from fusing with and entering cells. It is a twice-daily injection used only in people whose HIV keeps growing despite other medicines.

How it works

Established: to enter a cell, HIV's gp41 protein folds into a hairpin that pulls the viral and cell membranes together. Enfuvirtide binds the HR1 region of gp41 and blocks that fold, so fusion and entry fail (FDA label).

What research shows

  • TORO 1 and TORO 2 (treatment-experienced adults, 2:1 randomized, open-label): at 48 weeks, 46% vs 18% had at least a 1-log drop in viral load, and 23% vs 8% had HIV RNA under 50 copies/mL (FDA label).
  • Resistance develops through changes at gp41 HR1 positions 36-45 (FDA label).

Doses studied in people

Study or labelDose usedSource
FDA label (Fuzeon), adults90 mg subcutaneously twice daily1
FDA label (Fuzeon), children ≥11 kg2 mg/kg subcutaneously twice daily, maximum 90 mg twice daily1

Always used with other antiretrovirals per the label.

Read this first: these are the amounts given to participants in published studies or written on official prescribing labels, reported for reference. They are not recommendations. Trial doses were chosen for specific patients under medical supervision, and a dose that is safe in one person can be harmful in another.

Safety

  • Injection-site reactions in 98% of patients (FDA label).
  • Higher rate of bacterial pneumonia: 6.7 vs 0.6 events per 100 patient-years in phase 3 (FDA label).
  • Hypersensitivity in <1%; do not restart after a systemic reaction (FDA label).
  • Nerve pain lasting up to 6 months reported with the Biojector 2000 needle-free device (FDA label).
  • Common: diarrhea 31.7%, nausea 22.8%, fatigue 20.2% (FDA label).

Report side effects of any drug or product to the FDA through MedWatch. For a possible poisoning in the US, call Poison Control at 1-800-222-1222.

Storage and stability

Powder at 25°C; after reconstitution, refrigerate at 2-8°C and use within 24 hours (FDA label).

General lab handling, not instructions for personal use. See Storage and stability.

History

Developed by Trimeris with Roche, enfuvirtide (T-20) was approved by the FDA in 2003 as Fuzeon, the first HIV fusion inhibitor. Its use has declined as newer, easier oral drugs became available.

Common questions

Is enfuvirtide FDA-approved?

Yes. It was approved as Fuzeon in 2003 for HIV-1 in people who have already tried other treatments and still have the virus multiplying 1. It is prescription only 1.

How does enfuvirtide stop HIV?

HIV uses its gp41 protein to fold up and pull its membrane against a cell's membrane so it can get in 1. Enfuvirtide binds gp41 and blocks that fold, so the virus cannot fuse with and enter the cell 1.

What did the main trials find?

In the TORO 1 and TORO 2 trials, 46% of patients adding enfuvirtide had at least a tenfold drop in virus levels at 48 weeks, versus 18% without it 1. 23% versus 8% reached a virus level under 50 copies/mL 1.

What doses are on the FDA label?

The label lists 90 mg injected under the skin twice daily for adults, and 2 mg/kg twice daily for children of at least 11 kg, up to 90 mg 1. It is always used together with other HIV medicines 1.

What are the side effects?

Injection-site reactions happen in 98% of patients 1. Bacterial pneumonia was more common in trials (6.7 vs 0.6 events per 100 patient-years), and diarrhea, nausea and tiredness are also common 1.

Is enfuvirtide banned in sport?

It is not named on WADA's 2026 Prohibited List 90.

Related compounds

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Daptomycin

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Daptomycin is an antibiotic made by soil bacteria.

Sources

  1. Fuzeon (enfuvirtide) prescribing information FDA label
  2. ChEBI: enfuvirtide (CHEBI:608828) Journal
  3. WADA 2026 Prohibited List Regulatory

Last reviewed 2026-10-25 · How we research · Found an error? See our corrections policy.