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Evidence: HighPeptideDiscontinuedHIV fusion inhibitorFDA-approved 2003 · now discontinuedInjected twice daily

Enfuvirtide

A synthetic piece of HIV's own gp41 protein that blocks the virus from fusing with cells, the first drug of its kind

A synthetic peptide copied from part of HIV-1's gp41 envelope protein that blocks the virus from fusing with cells; approved in 2003 as Fuzeon, the first HIV fusion inhibitor.

At a Glance Read Research →
Overview

What is it?

To infect a cell, HIV merges its membrane with the cell's, a step driven by gp41, the transmembrane part of its envelope protein. Enfuvirtide binds gp41 and blocks that fusion. It was the first approved fusion inhibitor.

Two phase 3 trials, TORO 1 in the Americas and TORO 2 in Europe and Australia, enrolled people whose HIV resisted the three older drug classes. Added to an optimized regimen, enfuvirtide lowered viral load and raised CD4 counts more than the regimen alone over 24 weeks.

Drugs@FDA now lists Fuzeon as discontinued and DailyMed carries no current maker's label, so the dose and half-life here come from the trials and a pharmacokinetics review rather than a label.

Structured data

At a Glance

Every value in this table is printed from the Grey Peptides dataset, the same record the compound explorer and comparison tool read, so the three can never disagree.

ClassA synthetic peptide matching a region of HIV-1's gp41 envelope protein that blocks the virus from fusing with cells; approved as Fuzeon in 2003, the first HIV fusion inhibitor, and now listed as discontinued in the US.
FormulaC204H301N51O64
Molecular weight4492 g/mol
Half-lifeabout 3.8 hours after subcutaneous injection
Studied dose90 mg (twice daily, subcutaneous)
US statusDiscontinued
Evidence levelHigh
Last reviewed2026-10-02

Educational information, not medical advice. The doses on this page come from approved labels, published studies and, where no study exists, amounts reported by users. None is a recommendation for you. An unapproved compound has no established safe or effective human dose, and products sold for “research use only” are not made or tested for people. Talk to a doctor before acting on anything on this site, including before you start, stop or change any medicine or dose. Full medical disclaimer.

Interactive

Half-Life: How Much Remains

The dataset records a half-life of about 3.8 hours after subcutaneous injection for Enfuvirtide. After each half-life, half of what was in the circulation is gone, so about 3% remains after five. Real clearance varies with the person, the dose, the route and kidney or liver function; this is arithmetic on a published figure, not a dosing tool.

Time since a single dose
ElapsedTimeRemaining
1 half-life3.8 h50% remaining
2 half-lives7.6 h25% remaining
3 half-lives11.4 h12.5% remaining
4 half-lives15.2 h6.25% remaining
5 half-lives19 h3.125% remaining
Evidence

Published Research

The studies behind enfuvirtide, read from their PubMed abstracts.

Human1998

The first human study: T-20 into a vein, 16 adults

Sixteen adults with HIV received intravenous T-20 alone for 14 days at 3 to 100 mg twice daily. Viral load fell with dose; all four on 100 mg twice daily dropped below 500 copies/mL, a median fall of 1.96 log10.

PMID: 9809555
Human2003

TORO 1: the Americas, 501 patients

People in the Americas with HIV resistant to three drug classes were randomized 2:1 to enfuvirtide plus an optimized regimen or the regimen alone. At 24 weeks viral load fell 1.696 log10 against 0.764; CD4 counts rose by 76 against 32 cells/mm³.

PMID: 12637625
Human2003

TORO 2: Europe and Australia, 512 patients

Patients with a median of 12 previous drugs took enfuvirtide 90 mg twice daily plus an optimized regimen, or the regimen alone. At 24 weeks viral load fell 1.429 log10 against 0.648, and CD4 counts rose by 65.5 against 38.0 cells/mm³.

PMID: 12773645
Human2005

Both TORO trials pooled: 48-week safety, 997 patients

Injection-site reactions occurred in 98% of enfuvirtide patients and led 4.4% to stop. Pneumonia (6.7 against 0.6 events per 100 patient-years) and swollen lymph nodes (7.1 against 1.2) were more frequent than on the background regimen alone.

PMID: 16280695
Review2005

How the body handles it

At 90 mg twice daily under the skin, absorption is slow and almost complete (bioavailability 84.3%), the half-life is 3.8 hours and 92% is bound to plasma proteins. It showed little potential to interact with drugs processed by the main liver enzymes.

PMID: 15656696
Review2012

The injection-site reactions in detail

Injection-site reactions occur in nearly everyone treated, from little or nothing to cysts, nodules and scleroderma-like hardening; most are self-limited.

PMID: 23134996
Safety

Side Effects & Contraindications

Reported Side Effects

From the studies above.

● Injection-site reactions in 98% of patients, which led 4.4% to stop over 48 weeks (pooled TORO data)
● Pneumonia more often than on the background regimen alone: 6.7 against 0.6 events per 100 patient-years
● Swollen lymph nodes: 7.1 against 1.2 events per 100 patient-years

Contraindications & Cautions

There is no current US label to quote; from the EU product information summary (EMA).

● Allergy to enfuvirtide or any other ingredient of the product
● Tested athletes — see the Sport (WADA) row below
Questions

Frequently Asked Questions

?What is enfuvirtide?

A synthetic peptide copied from part of HIV-1's gp41 envelope protein. It blocks the virus from fusing with the cells it infects and was sold as Fuzeon, the first HIV fusion inhibitor.

?Is Fuzeon still available?

Drugs@FDA lists Fuzeon as discontinued in the US, and DailyMed carries no current maker's label. Its EU status today was not verified here.

?How was it taken?

In the phase 3 TORO trials, 90 mg was injected under the skin twice a day alongside other HIV drugs.

Bibliography

References

  1. [fda] US FDA, Drugs@FDA (openFDA): FUZEON (enfuvirtide), NDA 021481, original approval March 13, 2003, marketing status Discontinued. Read October 2, 2026.
  2. [other] European Medicines Agency. Fuzeon (enfuvirtide) EPAR: marketing authorisation granted May 27, 2003, renewed May 27, 2008. Read October 2, 2026.
  3. [clinical-trial] Kilby JM, et al. "Potent suppression of HIV-1 replication in humans by T-20, a peptide inhibitor of gp41-mediated virus entry." Nat Med, 1998;4(11):1302-7. PMID: 9809555.
  4. [clinical-trial] Lalezari JP, et al. "Enfuvirtide, an HIV-1 fusion inhibitor, for drug-resistant HIV infection in North and South America." N Engl J Med, 2003;348(22):2175-85. PMID: 12637625.
  5. [clinical-trial] Lazzarin A, et al. "Efficacy of enfuvirtide in patients infected with drug-resistant HIV-1 in Europe and Australia." N Engl J Med, 2003;348(22):2186-95. PMID: 12773645.
  6. [clinical-trial] Trottier B, et al. "Safety of enfuvirtide in combination with an optimized background of antiretrovirals in treatment-experienced HIV-1-infected adults over 48 weeks." J Acquir Immune Defic Syndr, 2005;40(4):413-21. PMID: 16280695.
  7. [pubmed] Patel IH, et al. "Pharmacokinetics, pharmacodynamics and drug interaction potential of enfuvirtide." Clin Pharmacokinet, 2005;44(2):175-86. PMID: 15656696.
  8. [pubmed] Mirza RA, et al. "Enfuvirtide and cutaneous injection-site reactions." J Drugs Dermatol, 2012;11(10):e35-8. PMID: 23134996.

Sources & Citations

Studies were read from their PubMed records; regulatory sources are listed below, read October 2, 2026.

Medical Disclaimer: This content is for educational and informational purposes only. It is not medical advice, and nothing here is an instruction to obtain or use any compound. Consult a licensed healthcare provider before making health decisions.

Last reviewed: 2026-10-02