Products
Fosamprenavir is commercially available in the form of film-coated tablets (Telzir). It has been approved in many countries since 2005.
Structure and properties
Fosamprenavir (C25H36N3O9PS, Mr = 585.6 g/mol) is present in drugs as fosamprenavir calcium. It is a prodrug that is rapidly biotransformed in the intestinal mucosa to the active metabolite amprenavir. Amprenavir itself (Agenerase) is no longer commercially available in many countries.
Effects
Fosamprenavir (ATC J05AE07) has antiviral properties. The effects of the active metabolite amprenavir are due to competitive inhibition of HIV protease, which is important for viral maturation and thus plays a central role in viral replication. Amprenavir is degraded by CYP3A4. The CYP inhibitor ritonavir is administered concomitantly to inhibit degradation and thus increase plasma concentrations of amprenavir.
Indications
In combination with low-dose ritonavir for the treatment of HIV infection as part of combination antiretroviral therapy.
Dosage
According to the SmPC. Medicines are usually taken twice daily, independent of meals.
Contraindications
- Hypersensitivity contraindicated
- Fosamprenavir should not be administered with CYP3A4 or CYP2D6 substrates, which have narrow therapeutic ranges. Combination with the CYP inducers rifampicin and St. John’s wort and some statins is also not indicated.
Full precautions can be found in the drug label.
Interactions
Fosamprenavir has a high potential for interaction. It is a substrate and also an inhibitor of CYP3A4. Ritonavir is also a CYP substrate and inhibitor.
Adverse effects
The most common possible adverse effects include diarrhea, hypercholesterolemia, triglyceride elevation, liver enzyme elevation, skin rash, headache, dizziness, sensory disturbances in the mouth, fatigue, nausea, vomiting, and abdominal pain.
