Fosamprenavir and Mycobutin

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 rifabutin together with fosamprenavir may increase the effects of rifabutin. Contact your doctor if you experience headache, nausea, vomiting, stomach pain, severe skin rash or itching, pale skin, weakness, easy bruising or bleeding, fever, chills, body aches, flu symptoms, or eye pain or redness, and vision loss. 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 amprenavir or its prodrug, fosamprenavir, may significantly increase the plasma concentrations of rifabutin and its pharmacologically active 25-O-desacetyl metabolite. The mechanism is amprenavir inhibition of CYP450 3A4, the isoenzyme responsible for the metabolic clearance of rifabutin and 25-O-desacetylrifabutin. In six healthy volunteers, amprenavir (1200 mg twice a day for 10 days) increased the mean steady-state peak plasma concentration (Cmax), area under the concentration-time curve (AUC) and trough plasma concentration (Cmin) of rifabutin (300 mg once a day for 10 days) by 119%, 193% and 271%, respectively, compared to administration of rifabutin alone. Mean steady-state Cmax, AUC, and Cmin of 25-O-desacetylrifabutin increased by 7.39-, 13.35-, and 32.9-fold, respectively. There were no statistically significant differences in the pharmacokinetics of amprenavir when coadministered with rifabutin. The combination was poorly tolerated, resulting in withdrawal of 5 of 11 subjects from the study. Adverse events consisted primarily of flu-like symptoms and leukopenia. Rifabutin given at regular dosages in combination with other protease inhibitors has been associated with uveitis secondary to rifabutin toxicity.

MANAGEMENT: To minimize the risk of rifabutin toxicity including leucopenia, uveitis, arthralgias and skin discoloration, product labellings recommend that rifabutin dosage be reduced by at least 75% of the normally recommended dosage in patients treated with amprenavir or fosamprenavir in combination with ritonavir. Some experts suggest decreasing the rifabutin dose from 300 to 150 mg if given daily but administering the full 300 mg dose during intermittent therapy (i.e. twice- or three-times- weekly directly observed therapy). A complete blood count should be performed at least weekly and as clinically indicated to monitor for development of neutropenia.

Fosamprenavir

Generic Name: fosamprenavir

Brand name: Lexiva, Telzir

Synonyms: n.a.

What is Fosamprenavir?

Mycobutin

Generic Name: rifabutin

Brand name: Mycobutin

Synonyms: n.a.

What is Mycobutin?