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Protease inhibitor (amprenavir prodrug)

Fosamprenavir

Brand names: Telzir

Fosamprenavir is a prodrug HIV protease inhibitor used, with low-dose ritonavir boosting, as part of combination antiretroviral therapy for HIV-1 infection.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.

Clinical monograph

How it works

It is hydrolysed to amprenavir, which inhibits HIV-1 protease and prevents cleavage of viral polyproteins, producing immature, non-infectious virions.

Prescribing in practice

  • It is a sulfonamide-derived drug and can cause serious skin reactions, so it should be used with caution in patients with sulfonamide allergy and stopped if a severe rash occurs.
  • It is extensively involved in cytochrome P450 metabolism and is usually boosted with ritonavir, leading to many clinically important drug interactions.
  • Like other protease inhibitors it can cause metabolic disturbances including dyslipidaemia and hyperglycaemia.

Monitoring

Monitor HIV viral load and CD4 count, lipids and blood glucose, hepatic function, and for rash or drug interactions.

Counselling the patient

  • Take with your boosting medicine exactly as prescribed.
  • Report any rash, particularly if severe or with blistering.
  • Tell your team about all other medicines, as interactions are common.

Evidence & guidelines

Fosamprenavir is recommended within boosted protease inhibitor regimens in UK (BHIVA) HIV treatment guidance.

Reference: BHIVA; SmPC; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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