Evidence Grade A — Regulatory approved. 828 published studies. 54 registered clinical trials.
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Enfuvirtide (sold as Fuzeon) is an injectable antiviral that stops HIV from entering human immune cells — the very first step in the infection process. It was the first "fusion inhibitor" approved for HIV and is reserved for patients whose virus has become resistant to other drug combinations. However, the requirement for twice-daily injections and near-universal injection-site reactions have made it a treatment of last resort.
Enfuvirtide is also known by these brand and alternate names:
828 published studies: 719 human, 20 animal, 104 in-vitro, 166 reviews
Enfuvirtide is marketed as Fuzeon (approved March 2003). It requires twice-daily subcutaneous injections, and injection-site reactions occur in nearly all patients (98%). In clinical trials (TORO-1 and TORO-2), enfuvirtide combined with an optimised background regimen achieved significantly greater viral suppression than background regimen alone in treatment-experienced patients.
Enfuvirtide represented a major advance when HIV drug resistance was a more pressing clinical challenge, but its use has declined substantially with the arrival of more convenient oral antiretrovirals. The twice-daily injection burden, injection-site reactions, high cost, and complex manufacturing (it is one of the largest synthetic peptides manufactured at scale) have limited its role to a last-resort option for patients with highly resistant HIV.
When HIV infects a cell, its surface protein gp41 must fold into a specific shape to fuse the viral envelope with the cell membrane. Enfuvirtide is a peptide that mimics part of gp41 and physically blocks this folding step, like jamming a zipper. Without this conformational change, the virus cannot merge with the cell and infection is prevented. This mechanism is effective against HIV strains that have developed resistance to drugs targeting later stages of the viral lifecycle.
Two major clinical trials (TORO-1 and TORO-2) demonstrated that adding enfuvirtide to an optimised drug regimen significantly improved viral suppression in patients with highly resistant HIV. When it was introduced in 2003, it represented an important advance for patients running out of treatment options. In practice, enfuvirtide's role has been drastically reduced by the arrival of oral drugs (particularly integrase inhibitors) that are more potent, better tolerated, and far more convenient. Injection-site reactions occur in 98% of patients, and the twice-daily injection schedule is a heavy burden. The drug is also one of the largest synthetic peptides ever manufactured at commercial scale, contributing to high costs. The manufacturer announced US discontinuation in August 2024, reflecting its minimal remaining clinical use.
PeptideTrace tracks 54 registered clinical trials for Enfuvirtide sourced from ClinicalTrials.gov.
Study of a New Anti-HIV Drug, T-20, in HIV-Infected Children
Adding New Drugs for HIV Infected Patients Failing Current Therapy
T-20 in HIV Patients With Prior Drug Treatment and/or Resistance to Each of the Three Classes of Anti-HIV Drugs
EMA Marketing Authorisation
Health Canada Market Authorisation
Enfuvirtide is a 36-amino-acid synthetic linear peptide (MW 4,492 Da) with an acetylated N-terminus and C-terminal carboxamide. Its sequence derives from the HR2 region of HIV-1 gp41 (residues 643-678). It interferes with HIV-1 entry into CD4+ T lymphocytes by blocking the membrane fusion step. Half-life approximately 3.8 hours, bioavailability 84.3%, 92% plasma protein binding, enabling twice-daily subcutaneous dosing at 90 mg.
Enfuvirtide competitively binds the HR1 groove of HIV-1 gp41, preventing the HR2 domain from folding back to form the six-helix bundle (6-HB). Without 6-HB formation, the conformational energy for membrane fusion is unavailable. Active against R5-, X4-, and dual-tropic HIV-1 (IC50 0.089-107 nM) but has no HIV-2 activity. Also acts as an agonist at FPR1 on phagocytes. The purely extracellular mechanism means minimal CYP450 drug-drug interaction potential.
Marketed as Fuzeon (SC injection, approved March 13, 2003). TORO 1 (N=491): viral load reduction -1.70 vs. -0.76 log10 (P<0.001); 37% vs. 16% achieved <400 copies/mL. TORO 2 (N=504): -1.43 vs. -0.65 log10 (P<0.0001); 28.4% vs. 12.2% achieved <400 copies/mL. 96-week extension (N=663): 26.5% <400 copies/mL, CD4+ increase +166 cells/mm3. Approved for HIV-1 in treatment-experienced adults and children >=6 years.
Vancomycin is marketed as Vancocin and Firvanq (approved 1958, with oral solution Firvanq approved 2018). It is the standard treatment for serious MRSA infections (bloodstream infections, endocarditis, pneumonia, bone infections) and is first-line for severe C. difficile colitis. Vancomycin requires therapeutic drug monitoring — blood levels must be checked regularly to ensure the dose is effective without causing kidney damage or hearing loss. The rise of vancomycin-resistant enterococci (VRE) and occasional vancomycin-intermediate S. aureus (VISA) strains represent ongoing challenges. Despite being nearly 70 years old, vancomycin remains irreplaceable for many serious infections, though newer alternatives like daptomycin and the lipoglycopeptides offer advantages in specific settings.
Zilucoplan is marketed as Zilbrysq (approved October 2023) for anti-acetylcholine receptor antibody-positive generalised myasthenia gravis in adults. Administered as a daily subcutaneous self-injection. In the RAISE trial, zilucoplan showed statistically significant improvements in both activities of daily living and quantitative muscle strength scores compared to placebo, with improvements evident from week one. Its key differentiator from existing complement inhibitors (eculizumab, ravulizumab) is the self-injectable format — those alternatives require hospital-based intravenous infusions. As with all complement inhibitors, patients require meningococcal vaccination before starting treatment due to increased susceptibility to meningococcal infection.
Daptomycin is marketed as Cubicin (approved September 2003). It is indicated for complicated skin and soft tissue infections and S. aureus bloodstream infections including right-sided endocarditis. Administered as a once-daily intravenous infusion. A key limitation is that daptomycin cannot be used for pneumonia — lung surfactant inactivates the drug. In the bacteraemia trial, daptomycin was non-inferior to vancomycin with significantly lower rates of kidney problems (11% versus 26%). Creatine kinase (CK) levels must be monitored during treatment, as daptomycin can cause muscle toxicity. Generics became available after patent expiry, significantly reducing cost.
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