Quick facts
- Class
- HIV-1 fusion inhibitor peptide
- Brand name
- Fuzeon (T-20)
- Approved for
- HIV-1 infection (treatment-experienced)
- Administration
- Subcutaneous injection
- Status
- FDA-approved, prescription-only
- Class
- HIV-1 fusion inhibitor peptide (36 aa)
- Brand name
- Fuzeon (T-20)
- Administration
- Subcutaneous injection
- Common side effect
- Injection-site reactions
Key takeaways
- Enfuvirtide (Fuzeon, T-20) is a 36-amino-acid peptide and the first approved HIV-1 fusion inhibitor.
- It blocks viral entry by binding gp41 and preventing the membrane fusion the virus needs to infect cells.
- It is used in combination therapy for treatment-experienced patients with limited remaining options.
- Injection-site reactions are very common and a key practical limitation of the twice-daily subcutaneous regimen.
- It is an approved, regulated prescription medicine, not a research chemical.
Overview
Enfuvirtide, sold as Fuzeon and also known as T-20, is a 36-amino-acid synthetic peptide used in the treatment of HIV-1 infection. It belongs to a class of antiretroviral drugs called fusion inhibitors and was the first drug in this class to reach the market. It is administered by subcutaneous injection.
Enfuvirtide is intended for treatment-experienced patients, meaning people whose HIV has developed resistance to or is no longer adequately controlled by other antiretroviral regimens. It is used in combination with other antiretroviral drugs rather than on its own, as part of a broader strategy to suppress the virus.
As an approved prescription medicine, enfuvirtide is regulated and used under medical supervision. Its development represented an important proof of concept that a peptide could effectively block a specific step in the HIV life cycle, expanding the options available for difficult-to-treat infections.
How it works
Enfuvirtide blocks the entry of HIV-1 into human immune cells. The virus uses a surface protein called gp41 to fuse its envelope with the membrane of a target cell. During this process, parts of gp41 fold together to pull the viral and cell membranes close enough to merge.
Enfuvirtide is a peptide that mimics a segment of gp41 and binds to the protein, preventing it from forming the structure needed for fusion. By interfering with this conformational change, the drug stops the virus from entering the cell, halting that round of infection before the viral genetic material can get inside.
Because it acts outside the cell at the entry stage, enfuvirtide works through a mechanism distinct from drugs that target later steps such as reverse transcription or protease activity. This complementary mode of action is why it is valued in patients whose virus has become resistant to other drug classes.
Clinical evidence
Enfuvirtide's clinical evidence comes largely from its development program, including the TORO studies, which evaluated the drug in treatment-experienced adults with HIV-1. These trials assessed adding enfuvirtide to an optimized background regimen compared with the background regimen alone, supporting its approval for this population.
The findings indicated that adding enfuvirtide improved viral suppression in patients who had limited remaining options due to drug resistance. This established a role for fusion inhibition as part of combination therapy in advanced or heavily treatment-experienced disease.
In practice, the requirement for twice-daily subcutaneous injection and the frequency of injection-site reactions have limited enfuvirtide's everyday use, particularly as newer oral agents and drug classes have become available. It is generally reserved for specific situations where other options are inadequate, and it remains an example of successful peptide-based antiviral design.
Dosing & side effects
Enfuvirtide is a prescription medicine that must be used under medical supervision as part of a combination antiretroviral regimen. This article does not provide dosing figures. It is reconstituted and given by subcutaneous injection, and patients are typically trained in proper injection technique and site rotation.
The most characteristic side effect is injection-site reactions, which are very common and can include pain, redness, hardening, and nodules at the sites where the drug is administered. These reactions are a major practical consideration and can affect adherence to therapy.
Other reported effects can include hypersensitivity reactions and, in studies, an observed association with certain infections such as pneumonia. As with any antiretroviral, use requires monitoring by an HIV specialist, and decisions about combining it with other drugs are individualized based on resistance testing and the patient's overall regimen.
Legal status
Enfuvirtide is an approved prescription medicine. It received regulatory approval from agencies including the US Food and Drug Administration and the European Medicines Agency for the treatment of HIV-1 infection in combination with other antiretroviral drugs in treatment-experienced patients.
As a regulated pharmaceutical, it is manufactured to strict quality standards and is available only by prescription through legitimate medical and pharmacy channels. It is intended for use within a managed HIV treatment plan overseen by qualified clinicians.
Enfuvirtide is not a research chemical or gray-market substance. Its place in therapy has narrowed over time as newer agents have emerged, but it remains an approved option and a notable milestone as the first HIV fusion inhibitor to be developed and marketed.
Frequently asked questions
What is enfuvirtide used for?
It is used to treat HIV-1 infection in combination with other antiretroviral drugs, specifically in treatment-experienced patients whose virus is resistant to or inadequately controlled by other regimens.
How does enfuvirtide differ from other HIV drugs?
It works at the entry stage by blocking the viral protein gp41 and preventing fusion with the cell, rather than targeting later steps such as reverse transcription or protease activity inside the cell.
Why does enfuvirtide need to be injected?
As a peptide it would be broken down by digestion if swallowed, so it is given by subcutaneous injection. Patients are usually trained in injection technique and rotating sites.
What is the most common side effect?
Injection-site reactions are very common, including pain, redness, hardening, and nodules at the injection sites. These can affect comfort and adherence to the twice-daily regimen.
Is enfuvirtide still widely used?
Its everyday use has declined as newer oral agents and drug classes have become available. It remains an approved option generally reserved for situations where other treatments are inadequate.
References
Each source links to its original record — peer-reviewed studies, regulator pages, or reference texts, labelled by type. We summarize findings neutrally; a citation is a reference, not an endorsement, and not a claim that its authors reviewed this page.
- Fung HB, Guo Y. Enfuvirtide: a fusion inhibitor for the treatment of HIV infection. Clin Ther. 2004. Peer-reviewed study
- Lazzarin A. Enfuvirtide: the first HIV fusion inhibitor. Expert Opin Pharmacother. 2005. Peer-reviewed study
- Poveda E, Briz V, Soriano V. Enfuvirtide, the first fusion inhibitor to treat HIV infection. AIDS Rev. 2005. Peer-reviewed study
- Jamjian MC, McNicholl IR. Enfuvirtide: first fusion inhibitor for treatment of HIV infection. Am J Health Syst Pharm. 2004. Peer-reviewed study
- Chen RY, Kilby JM, Saag MS. Enfuvirtide. Expert Opin Investig Drugs. 2002. Peer-reviewed study
- Dando TM, Perry CM. Enfuvirtide. Drugs. 2003. Peer-reviewed study