Enfuvirtide

Enfuvirtide is primarily used in HIV research to study viral entry mechanisms, test combination therapies, and develop new fusion inhibitors. It serves as a research tool for understanding how HIV enters cells and for testing against drug-resistant viral strains.

Unlike reverse transcriptase inhibitors and protease inhibitors that work after HIV enters cells, enfuvirtide prevents the virus from entering cells in the first place. It blocks the final step of viral fusion by binding to gp41 protein on the virus surface.

Enfuvirtide is a 36-amino acid peptide that gets broken down by digestive enzymes if taken orally. Subcutaneous injection bypasses the digestive system, achieving 84% bioavailability compared to essentially zero oral absorption.

Injection site reactions occur in nearly all users, including pain, redness, and hard nodules. Other common effects include increased risk of bacterial pneumonia, peripheral neuropathy, insomnia, and gastrointestinal symptoms.

Resistance typically emerges within 12-48 weeks of treatment, primarily through mutations in the gp41 HR1 region at amino acid positions 36-45. The rate depends on baseline viral load and adherence to combination therapy.

The powder form must be refrigerated at 2-8°C. Once reconstituted, the solution can be stored at room temperature for up to 24 hours but should be used immediately for optimal potency.

Enfuvirtide was discontinued commercially in 2009 due to high costs and injection requirements, but it remains available for research and compassionate use. Newer oral entry inhibitors have largely replaced it in clinical practice.

In vitro studies show 50% inhibition (IC50) at concentrations of 1.8-8.5 ng/mL, while therapeutic plasma levels of 2000-3000 ng/mL are needed in vivo due to protein binding and tissue distribution factors.