Immune & defense HIV fusion inhibitor peptide
Enfuvirtide
Regulatory status
Status at a glance
503A compounding status
Not nominated
We found no pending nomination for the 503A bulks list. Unless the substance has another legal pathway (for example, a USP monograph or use in an FDA-approved drug), 503A pharmacies generally may not compound with it.
- FDA approval
- An FDA-approved product contains this peptide
- 503B outsourcing
- Not determined
- Anti-doping (WADA)
- Not on the WADA Prohibited List
- DEA schedule
- Not a controlled substance
About peptide status
Most peptides discussed here are not FDA-approved for any use, and products labeled “research use only” are not for human use. Removal from Category 2 does not authorize compounding. PCAC votes are non-binding recommendations; FDA and HHS make the final decisions.
This is not medical or legal advice, and we do not publish dosing, sourcing or reconstitution information. Talk with a licensed clinician before using any peptide.
If you think you are having a medical emergency, call 911.
Key takeaway
Enfuvirtide (formerly sold as Fuzeon) is a peptide HIV drug that blocks the virus from entering CD4 immune cells, the first of the so-called fusion inhibitors. It was used in treatment-experienced patients whose virus is no longer controlled by other antiretrovirals. It was FDA-approved in the U.S. in 2003, but Fuzeon was discontinued there in February 2025.
At a glance
- What it is
- An HIV-1 fusion (entry) inhibitor, a 36-amino-acid peptide
- Approved for
- HIV-1 infection in treatment-experienced patients, in combination with other antiretrovirals (approved in 2003; no longer sold in the U.S.)
- Key fact
- In the TORO trials, adding enfuvirtide to an optimized regimen significantly lowered viral load versus the regimen alone
- Route
- Subcutaneous injection, twice daily
- Evidence strength
- FDA approved
Summary
Enfuvirtide (Fuzeon) blocks HIV from entering CD4 cells. See how this fusion inhibitor works, who used it, its 2003 FDA approval, and its 2025 discontinuation.
What is enfuvirtide?
Enfuvirtide, formerly sold under the brand Fuzeon, is a 36-amino-acid synthetic peptide that blocks HIV from entering host cells. It was the first in a class called fusion inhibitors (or entry inhibitors) and is used in people whose HIV has become resistant to multiple other drugs. It was developed under the code T-20 and approved in the United States in 2003.
How does enfuvirtide work?
Enfuvirtide blocks the step where HIV fuses its envelope with the membrane of a CD4 immune cell to get inside. The viral surface protein gp41 must fold on itself, forming a hairpin-like structure, to pull the two membranes together. Enfuvirtide mimics a segment of gp41 and binds the region the protein needs to grip, preventing that folding. Without it, the virus cannot complete fusion and cannot enter the cell.
Because it works outside the cell at the point of entry, its mechanism is entirely different from the drugs that act inside the cell on reverse transcriptase, protease, or integrase, which is why it retains activity against virus resistant to those classes. In the TORO trials, adding enfuvirtide to an optimized background regimen produced a significantly greater reduction in HIV-1 RNA than the background regimen alone. It must be injected twice daily, which, with frequent injection-site reactions, limits its use to situations where other options are exhausted.
Is it FDA-approved?
Editor’s note
Status: Enfuvirtide was approved by the FDA in 2003 for HIV-1 infection in treatment-experienced patients with ongoing viral replication despite antiretroviral therapy. Its maker discontinued Fuzeon in the U.S. on February 28, 2025, citing reduced need as newer treatments became available.
Category: FDA-approved · Primary body area: Immune & defense
Enfuvirtide was approved by the FDA in 2003 for HIV-1 infection in treatment-experienced patients with ongoing viral replication despite antiretroviral therapy. Its maker discontinued Fuzeon in the U.S. on February 28, 2025, citing reduced need as newer treatments became available.
What is enfuvirtide prescribed for?
Enfuvirtide was prescribed, in combination with other antiretrovirals, for HIV-1 infection in treatment-experienced patients whose virus was replicating despite current therapy. It was generally reserved for people with multidrug-resistant HIV because of the twice-daily injections.
What are the side effects?
Common side effects include:
- Injection-site reactions such as pain, hardened lumps, redness, and cysts, which occur in nearly all patients
- Diarrhea and nausea
- Fatigue
More serious considerations include:
- An increased rate of bacterial pneumonia
- Hypersensitivity reactions, which can recur if the drug is restarted
Sources: FDA prescribing information for Fuzeon; the TORO 1 trial (Lalezari et al., The New England Journal of Medicine, 2003, DOI: 10.1056/NEJMoa035026), indexed on PubMed. This document is educational and does not constitute medical advice.
Registered human trials
0 registered human trials on ClinicalTrials.gov that we reviewed
Sources
- [1]
- [2]
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