Is enfuvirtide FDA-approved, and what does the research show?

What is enfuvirtide?

Enfuvirtide is a medicine for HIV-1 infection that was sold under the brand name Fuzeon ³. Its patient leaflet calls HIV-1 "the virus that causes Acquired Immune Deficiency Syndrome (AIDS)" ³. The label describes the drug as "a linear 36-amino acid synthetic peptide" ³. A peptide is a short chain of amino acids, and this one is built synthetically from amino acids that occur in nature ³.

Its class is the fusion inhibitors ⁵, ³. The label calls it "an inhibitor of the fusion of HIV-1 with CD4 cells," the white blood cells the virus infects ³. It is an antiretroviral, the name for a drug that acts against HIV, and the label has it used only alongside other antiretrovirals ³.

Enfuvirtide is not a wellness, weight-loss or performance peptide. It was a treatment for people whose HIV-1 kept multiplying despite other drugs ³. The label says it "has not been studied in non-HIV infected individuals" ³.

Is enfuvirtide FDA-approved?

No longer. FDA approved Fuzeon (enfuvirtide) on March 13, 2003, under NDA 021481, and withdrew the approval as of November 9, 2026 ¹, ². An NDA is a new drug application, the file under which FDA approves a drug. Drugs@FDA lists Fuzeon's marketing status as "Discontinued" as of November 9, 2026, the date of the record's data ¹. Drugs@FDA's data of November 9, 2026, lists one enfuvirtide application, NDA 021481 ¹.

The company's own statement gives the background. Genentech, the Roche Group company that distributed Fuzeon in the United States, issued it on August 19, 2024 ³, ⁴. It said that on February 28, 2025, it would "discontinue all marketing and commercial distribution of Fuzeon" in the United States ⁴. It named among its reasons "evolving clinical practice and significantly reduced medical need due to the novel alternative treatment options targeting the same indication" ⁴. It added: "This action is not related to any quality, safety, or efficacy issues regarding the product" ⁴.

Those are the company's words, not FDA's ⁴. FDA's notice says only that the applicants "informed FDA that these drug products are no longer marketed" and asked for withdrawal ². The statement also says: "Alternative treatment options for HIV are commercially available" ⁴.

Fuzeon was a prescription medicine, and its labeling is marked "Rx only" ³. The latest label in FDA's record was revised in August 2019 ¹, ³. It says Fuzeon "in combination with other antiretroviral agents is indicated for the treatment of HIV-1 infection in treatment-experienced patients with evidence of HIV-1 replication despite ongoing antiretroviral therapy" ³. In the patient leaflet's plainer words, that means people "who have taken other antiretroviral medicines and whose HIV-1 levels have continued to increase while on treatment" ³.

The label covers adults and children who weigh at least 11 kilograms ³. Its patient leaflet says safety and effectiveness in children under 6 years of age are not known ³. The label lists that one indication and no other ³.

See the FDA status of every peptide, updated weekly.

How does enfuvirtide work?

To get inside a cell, the label explains, HIV-1 must merge its own outer membrane with the cell's, a step called fusion ³. Enfuvirtide "interferes with the entry of HIV-1 into cells by inhibiting fusion of viral and cellular membranes" ³.

It does this by binding to gp41, a protein on the envelope of the virus ³. The label says it attaches to a region of gp41 called HR1 and prevents the changes of shape that fusion requires ³. Shown in cells: virus samples resistant to three other classes of HIV drugs were still susceptible to enfuvirtide ³.

The label sets two limits on that picture ³. Enfuvirtide "has no activity against HIV-2," a second type of the virus ³. And HIV-1 can become resistant to it. Among 277 trial subjects whose treatment had failed by week 48, 249 carried virus that had become more than four times less susceptible ³.

The label has prescribers tell patients that it "must be taken as part of a combination antiretroviral regimen" ³. Used alone, it says, the drug "may lead to rapid development of virus resistant to FUZEON and possibly other agents of the same class" ³.

What does the research show?

The evidence for the approved use comes from two phase 3 trials, TORO 1 and TORO 2 ⁵, ⁶. Phase 3 trials are the large studies that precede an approval. Both were randomized, meaning chance decided each patient's treatment, and open-label, meaning patients and doctors knew who received the drug ⁵, ³.

The design was the same in both ⁵, ⁶. Every patient received an "optimized background regimen" of three to five HIV drugs, chosen for that patient with the help of resistance tests ⁵, ⁶, ³. Two patients in three were then assigned to add enfuvirtide, which the trials gave twice a day ⁵, ⁶, ³. The rest, the control group, took the background drugs alone ⁵, ⁶.

Studied in people: TORO 1 randomized 501 patients at 48 sites in the United States, Canada, Mexico and Brazil ⁵. It was published online on March 13, 2003 ⁵. To enter, patients needed at least six months of earlier treatment with three classes of HIV drugs, resistance to those classes, or both ⁵. They also needed at least 5,000 copies of HIV-1 RNA, the genetic material of the virus, in each milliliter of plasma, the liquid part of blood ⁵.

That count is the viral load, and the trials report its change on a logarithmic scale, where a fall of 1 is a tenfold drop ⁵. Among the 491 patients analyzed, the mean fall at 24 weeks was 1.696 log10 copies per milliliter in the enfuvirtide group ⁵. In the control group it was 0.764 (P < 0.001, a difference very unlikely to be chance) ⁵. The CD4 cell count, the trials' measure of immune benefit, started at a median of 75.5 cells per cubic millimeter with enfuvirtide and 87.0 in the control group ⁵. It rose by a mean of 76 in the enfuvirtide group and 32 in the control group (P < 0.001) ⁵.

Studied in people: TORO 2, in Europe and Australia, randomized 512 patients and appeared in the issue of May 29, 2003 ⁶. To enter, patients needed earlier treatment with each of the three drug classes, documented resistance to each, or both ⁶. They also needed at least 5,000 copies of HIV-1 RNA per milliliter ⁶. They had a median of seven years of earlier treatment and had received a median of 12 antiretroviral drugs ⁶.

Of the 512, 335 in the enfuvirtide group and 169 in the control group were analyzed ⁶. At 24 weeks the viral load had fallen by 1.429 log10 in the enfuvirtide group and 0.648 in the control group (P < 0.001) ⁶. The CD4 count rose by a mean of 65.5 and 38.0 cells per cubic millimeter (P = 0.02) ⁶.

The label pools the two trials at 48 weeks: 663 subjects assigned to enfuvirtide and 334 to the background drugs alone ³. A tenfold or greater fall in viral load was reached by 304 of the 663 (46 percent) and 61 of the 334 (18 percent) ³. Viral load was below 50 copies per milliliter in 154 (23 percent) and 27 (8 percent) ³. The mean CD4 gain was 91 cells per cubic millimeter with enfuvirtide and 45 without it ³.

After week 8, control patients with virological failure, the label's term for treatment that was failing, could add enfuvirtide ³. Of the 334 control patients, 220 did so ³. Fifteen of the 663 subjects assigned to enfuvirtide died (2 percent) ³. So did 5 of the 112 who stayed on background drugs alone (4 percent) and 2 of the 220 who switched (1 percent) ³. Studied in children: 63 treatment-experienced subjects aged 5 through 16 received enfuvirtide in two open-label trials with no comparison group ³. In the first, 6 of 11 children had a tenfold fall in viral load at week 48 ³. In the second, 17 of 52 did, and 32 of the 52 completed 48 weeks ³.

Carcinogenicity studies, the long animal tests for cancer risk, "have not been conducted" ³. The trials also held too few subjects aged 65 and over to show whether they respond differently ³.

What are the side effects?

The label's safety record covers 2,131 subjects who received at least one dose ³. Its rates come from the two TORO trials pooled at 48 weeks, in treatment-experienced people with HIV-1 ³. Almost everyone reacted where the drug was injected: 98 percent of subjects had at least one injection site reaction ³. Pain or discomfort was recorded in 96 percent, redness in 91 percent, hardening of the skin in 90 percent, and nodules or cysts in 80 percent ³. Itching was recorded in 65 percent and bruising in 52 percent ³.

Seven percent of subjects stopped treatment because of these reactions (4 percent) or "difficulties with injecting" such as "injection fatigue and inconvenience" (3 percent) ³. Infection at the injection site, including abscess, was reported in 1.7 percent of adults ³. Among adolescents it was more frequent, in 3 of 28 ³.

Time on treatment differed between the groups: 557 patient-years with enfuvirtide and 162 without, a patient-year being one patient followed for one year ³. So the label states other events per 100 patient-years ³. Diarrhea, nausea and fatigue were the most frequent, and each was reported at a higher rate with background drugs alone ³. Diarrhea, for example, ran at 38 per 100 patient-years with enfuvirtide and 73 without it ³.

Weight loss appears on the label as an adverse event, not a benefit ³. "Weight decreased" was recorded at grade 2 or above in 6.6 percent of the 663 enfuvirtide subjects ³. The rate was 7.9 per 100 patient-years with enfuvirtide against 6.2 with background drugs alone ³. Decreased appetite ran at 3.8 against 2.5 ³. These were people with HIV-1 that earlier drugs had failed to control, not people seeking to lose weight ³.

Pneumonia is a label warning ³. In the trials it was reported in 2.7 percent of enfuvirtide subjects, or 3.2 events per 100 patient-years, against 0.6 per 100 patient-years in the control arm ³. Counting every pneumonia diagnosis, the label gives 6.9 percent, or 6.7 events per 100 patient-years, against 0.6 per 100 patient-years ³. About half of those subjects needed a hospital stay ³. Three deaths in the enfuvirtide arm were attributed to pneumonia, all in subjects with "serious concomitant AIDS-related illnesses" ³.

A later observational study, which watched patients without assigning treatment, followed 740 patients on enfuvirtide and 1,110 not on it ³. Pneumonia ran at 3.2 and 1.8 events per 100 patient-years ³. The adjusted hazard ratio, a measure of relative risk, was 1.34, with a 95 percent confidence interval of 0.90 to 2.00 ³. The label concludes that "it is not possible to exclude an increased risk of pneumonia" and calls the link to the drug "unclear" ³.

The label's one contraindication is "known hypersensitivity to FUZEON or any of its components" ³. Systemic hypersensitivity, an allergic reaction of the whole body, occurred in fewer than 1 percent of subjects ³. It included "rash, fever, nausea and vomiting, chills, rigors, hypotension, and/or elevated serum liver transaminases" ³. The label says therapy "should not be restarted" after such a reaction ³.

Other warnings are narrower ³. A needle-free injector, the Biojector 2000, was linked to nerve pain "lasting up to 6 months," bruising and hematomas ³. Patients on anticoagulants, or with hemophilia or other clotting disorders, "may have a higher risk of post-injection bleeding" ³.

The label also warns of immune reconstitution syndrome: as the immune system responds to HIV treatment, it may mount an inflammatory response to lingering infections ³. For a person without HIV, the label notes a "theoretical risk" that antibodies to enfuvirtide could cause a false positive on one type of HIV test ³. Since approval, deposits of amyloid in the skin at the injection site have been reported ³.

In pregnancy, the label says the data "are not sufficient to adequately assess the risk of birth defects" ³. The label says to "instruct mothers not to breastfeed if they are receiving FUZEON" ³.

In sport

Enfuvirtide is not named on WADA's 2026 Prohibited List ⁷. WADA is the World Anti-Doping Agency. The list's section S2 covers peptide hormones, growth factors, related substances and mimetics, and enfuvirtide is not among the substances it names ⁷.

The list's section S0 reads: "Any pharmacological substance which is not addressed by any of the subsequent sections of the List and with no current approval by any governmental regulatory health authority for human therapeutic use (e.g. drugs under pre-clinical or clinical development or discontinued, designer drugs, substances approved only for veterinary use) is prohibited at all times" ⁷. FDA withdrew Fuzeon's approval as of August 5, 2026 ². The European Medicines Agency's page for Fuzeon, as read on November 10, 2026, states "This medicine is authorised for use in the European Union" ⁸.

What JumpstartMD offers

JumpstartMD does not prescribe enfuvirtide. Our peptide library covers it so you have the facts on its FDA status and the evidence, current as of November 10, 2026.

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Compounded medications are not FDA-approved, and FDA does not review their safety, effectiveness, or quality before they are marketed. A licensed clinician decides after an evaluation whether a peptide is appropriate for you, and not every patient will qualify.