Efavirenz Capsules and Fosamprenavir

In the database of official manuals used in the service creation an interaction registered by statistical results of studies was found, which can either lead to negative consequences for the patient health or strengthen a mutual positive effect. A doctor should be consulted to address the issue of joint drug administration.

Using efavirenz together with fosamprenavir may decrease the effects of fosamprenavir. Contact your doctor if your condition changes. If your doctor does prescribe these medications together, you may need a dose adjustment or special test to safely use both medications. It is important to tell your doctor about all other medications you use, including vitamins and herbs. Do not stop using any medications without first talking to your doctor.

ADJUST DOSE: Coadministration with efavirenz may decrease the plasma concentrations of amprenavir. The mechanism is efavirenz induction of CYP450 3A4, the isoenzyme responsible for the metabolic clearance of amprenavir. In one study, median plasma amprenavir trough level (Cmin) was 25% of the expected mean following 14 days of coadministration of amprenavir (1200 mg twice a day) and efavirenz (600 mg once a day) in seven HIV-infected patients. Overall, six of the seven patients had subtherapeutic amprenavir levels, and three had amprenavir Cmin values that were below 20% of the expected mean by as early as day 7. The addition of ritonavir (100 mg twice a day) to reduced dosages of amprenavir (450 to 900 mg twice a day) in the six patients resulted in increased amprenavir trough levels by 15- to 90-fold. In another study, efavirenz decreased the mean steady-state peak plasma concentration (Cmax), systemic exposure (AUC) and Cmin of amprenavir by 33%, 24% and 43%, respectively, in nine antiretroviral-experienced HIV patients treated with amprenavir, abacavir, and various nucleoside reverse transcriptase inhibitors. Amprenavir did not affect the pharmacokinetics of efavirenz.

MANAGEMENT: The dosage of amprenavir or its prodrug, fosamprenavir, should probably be increased when coadministered with efavirenz in the absence of ritonavir as a pharmacokinetic booster, although appropriate dosages with respect to safety and efficacy have not been established. Fosamprenavir labeling recommends an additional 100 mg/day (300 mg total) of ritonavir when efavirenz is administered with the fosamprenavir-ritonavir once-daily regimen based on pharmacokinetic studies. No change in the ritonavir dose is required when efavirenz is administered with the fosamprenavir-ritonavir twice-daily regimen.

Efavirenz Capsules

Generic Name: efavirenz

Brand name: Sustiva

Synonyms: Efavirenz

What is Efavirenz Capsules?

Fosamprenavir

Generic Name: fosamprenavir

Brand name: Lexiva, Telzir

Synonyms: n.a.

What is Fosamprenavir?