Fosamprenavir Dosage & Rx Info | Uses, Side Effects

Fosamprenavir Generic Name & Formulations

Legal Class

General Description

Fosamprenavir (as calcium) 700mg; tabs; (prodrug of amprenavir).

Pharmacological Class

HIV-1 protease inhibitor.

How Supplied

Contact supplier

Manufacturer

Various generic manufacturers

Mechanism of Action

Fosamprenavir is a prodrug that is rapidly hydrolyzed to amprenavir by cellular phosphatases in the gut epithelium as it is absorbed. Amprenavir is an inhibitor of HIV-1 protease. Amprenavir binds to the active site of HIV-1 protease and thereby prevents the processing of viral Gag and Gag-Pol polyprotein precursors, resulting in the formation of immature non-infectious viral particles.

Fosamprenavir Indications

Indications

HIV-1 infection.

Fosamprenavir Dosage and Administration

Adult

Therapy-naive: 1.4g twice daily; or fosamprenavir 1.4g + ritonavir 200mg once daily; or fosamprenavir 1.4g + ritonavir 100mg once daily; or fosamprenavir 700mg + ritonavir 100mg twice daily. Protease inhibitor-experienced: fosamprenavir 700mg + ritonavir 100mg twice daily. Hepatic impairment: see full labeling for dose adjustments.

Children

Protease inhibitor-naive (<4wks) or Protease inhibitor-experienced (<6mos): not recommended. Protease inhibitor-naive (≥4wks–18yrs) or Protease inhibitor-experienced (≥6mos): <11kg: fosamprenavir 45mg/kg + ritonavir 7mg/kg twice daily; 11–<15kg: fosamprenavir 30mg/kg + ritonavir 3mg/kg twice daily; 15–<20kg: fosamprenavir 23mg/kg + ritonavir 3mg/kg twice daily; ≥20kg: fosamprenavir 18mg/kg + ritonavir 3mg/kg twice daily. Alternatively, Protease inhibitor-naive (≥2yrs): fosamprenavir 30mg/kg twice daily. For all: do not exceed the adult dosage (see full labeling). Other dosing considerations: see full labeling.

Fosamprenavir Contraindications

Contraindications

Concomitant alfuzosin, cisapride, lurasidone, pimozide, ergots, midazolam, triazolam, St. John's wort, rifampin, lovastatin, simvastatin, delavirdine, sildenafil (Revatio; when used for treating PAH). Concomitant flecainide, or propafenone with ritonavir-boosted fosamprenavir.

Fosamprenavir Boxed Warnings

Not Applicable

Fosamprenavir Warnings/Precautions

Warnings/Precautions

Sulfonamide allergy. Hepatic impairment: see full labeling. Do not exceed recommended dose. Discontinue if severe or moderate rashes accompanied by systemic symptoms occur. Monitor lipids, liver function, and for hyperglycemia, increase in body fat, immune reconstitution syndrome. Hemophilia: monitor for spontaneous bleeding. Interrupt or discontinue if nephrolithiasis occurs. Elderly. Pregnancy. Nursing mothers: not recommended.

Fosamprenavir Pharmacokinetics

Absorption

Time to peak amprenavir concentration: between 1.5 and 4 hours.

Distribution

Plasma protein bound: ~90%.

Metabolism

Hepatic (CYP3A4).

Elimination

Fecal (>90%), renal. Half-life: ~7.7 hours.

Fosamprenavir Interactions

Interactions

See Contraindications. Life-threatening arrhythmias possible with amiodarone, lidocaine (systemic), quinidine. Concomitant salmeterol, boceprevir, simeprevir, ketoconazole or itraconazole (doses >200mg/day), paritaprevir/ritonavir/ombitasvir/dasabuvir, or nevirapine without ritonavir: not recommended. Reduce rifabutin dose by at least ½ (or by 75% if with ritonavir) and monitor for neutropenia (do weekly CBCs). Potentiates atorvastatin (max atorvastatin 20mg/day), sildenafil, tadalafil, vardenafil; reduce doses of these. May potentiate fluticasone (consider alternative therapy), trazodone (reduce trazodone dose). Monitor with antiarrhythmics (eg, amiodarone), anticonvulsants (eg, phenytoin), H₂ blockers, immunosuppressants, tricyclics, warfarin, drugs that affect or are affected by CYP3A4 (eg, azole antifungals, certain benzodiazepines, calcium channel blockers, NNRTIs, protease inhibitors, statins, steroids). May antagonize, or be antagonized by combined hormonal contraceptives (use alternative non-hormonal methods), methadone, paroxetine. Concomitant dolutegravir (with ritonavir-boosted fosamprenavir): give dolutegravir 50mg twice daily; use alternative if known or suspected integrase inhibitor resistance. Concomitant bosentan, colchicine, quetiapine, maraviroc (adjust doses; see full labeling).

Fosamprenavir Adverse Reactions

Adverse Reactions

Diarrhea, nausea, headache, rash (may be serious, eg, Stevens-Johnson), fatigue, vomiting and neutropenia (esp. children); hypertriglyceridemia, elevated liver enzymes, increase in body fat, immune reconstitution syndrome, hemolytic anemia.

Fosamprenavir

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