II. Indications
- HIV Infection (as part of combination therapy)
III. Contraindications
- Sulfonamide Allergy (Exercise caution if used)
- Age <6 months (per HIV Treatment guidelines)
IV. Mechanism
- See Protease Inhibitor
- Fosamprenavir is a prodrug, metabolized in vivo to amprenavir (Agenerase)
- Amprenavir is a synthetic derivative of hydroxyethylamine Sulfonamide, a Protease Inhibitor
V. Medications
- Fosamprenavir is typically taken with Ritonavir (Fosamprenavir/r)
- Unboosted Fosamprenavir is not typically recommended
- All adverse effects and Drug Interactions on this page assume administration with Ritonavir
- Tablets: 700 mg
- May take with or without food
- Suspension: 50 mg/ml
- Take with food (and better tolerated when refrigerated)
VI. Dosing: Adult
-
General
- Repeat dose if patient vomits within 30 minutes of dose
- HIV Treatment guidelines recommend only twice daily dosing regimen
- Package insert also describes once daily dosing in treatment naive patients (not listed here due to guidelines)
- Standard Dose
- Fosamprenavir 700 mg orally twice daily AND
- Ritonavir 100 mg orally twice daily
- Reduced Dose in Hepatic Dysfunction (adults only, pediatric doses not affected)
- Mild hepatic dysfunction (Child-Pugh Score 5 to 6)
- Fosamprenavir 700 mg orally twice daily AND
- Ritonavir 100 mg orally ONCE daily
- Moderate hepatic dysfunction (Child-Pugh Score 7 to 9)
- Fosamprenavir 450 mg orally twice daily AND
- Ritonavir 100 mg orally ONCE daily
- Severe hepatic dysfunction (Child-Pugh Score >9)
- Fosamprenavir 300 mg orally twice daily AND
- Ritonavir 100 mg orally ONCE daily
- Mild hepatic dysfunction (Child-Pugh Score 5 to 6)
VII. Dosing: Child (age >6 months)
-
General
- Repeat dose if patient vomits within 30 minutes of dose
- Take suspension with food (but tablets with or without food)
- Weight <11 kg: Fosamprenavir 45 mg/kg and Ritonavir 7 mg/kg, both taken orally twice daily
- Weight 11 to 15 kg: Fosamprenavir 30 mg/kg and Ritonavir 3 mg/kg, both taken orally twice daily
- Weight 15 to 20 kg: Fosamprenavir 23 mg/kg and Ritonavir 3 mg/kg, both taken orally twice daily
- Weight >20 kg: Fosamprenavir 18 mg/kg and Ritonavir 3 mg/kg, both taken orally twice daily
- Maximum (adult dose)
- Fosamprenavir 700 mg (weight >39 kg) orally twice daily AND
- Ritonavir 100 mg (weight >33 kg) orally twice daily
VIII. Adverse Effects
- See Protease Inhibitor for adverse effects attributed to the class
- Perioral Paresthesias
-
Hyperlipidemia
- Monitor lipid panel at baseline and periodically
- Rash (19%)
- Stevens-Johnson Syndrome risk
- Severe in some cases
IX. Safety
- Avoid in Lactation
- Unknown safety in pregnancy (avoid)
X. Drug Interactions
- Multiple Drug Interactions as a CYP3A4 inhibitor
- See Protease Inhibitor
- As with other Protease Inhibitors, check a formal Drug Interaction application before prescribing
-
Aluminum Hydroxide and Magnesium Hydroxide Antacid
- Reduced Fosamprenavir absorption
-
Statins (esp. Atorvastatin)
- Limit to lowest effective dose (Atorvastatin 20 mg/day)
-
Rifabutin
- Monitor Complete Blood Count (baseline and weekly)
-
Tricyclic Antidepressants
- Monitor levels
-
Immunosuppressants
- Monitor levels
- Methadone
-
Azole Antifungals (esp. Ketoconazole, Itraconazole)
- Limit to low dose (e.g. ketonazole 200 mg)
- Vardenafil
- Limit Vardenafil dose to 2.5 mg/day
-
Oral Contraceptives
- Use other forms of Contraception instead
XI. Resources
- Fosamprenavir (DailyMed)