AEGiS-GMHC: Treatment Briefs: Viagra and Protease Inhibitors

Important note: Information in this article was accurate in 1998. The state of the art may have changed since the publication date.

Treatment Briefs: Viagra and Protease Inhibitors

Treatment Issues, Volume 12, Number 5 - May 1998
Dave Gilden

Everyone who uses Pfizer's new anti-impotence drug Viagra should know by now that it should not be used with poppers, or indeed any other nitrate compound (such as nitroglycerin, which is administered during heart attacks). Nitrates and Viagra have complementary effects, and when present together can lead to dangerous drops in blood pressure.

Many people with HIV are still wondering, though, about Viagra's effect on protease inhibitors since Viagra is metabolized in the liver by the same CYP3A4 enzyme that protease inhibitors are. According to Pfizer, there should be little effect on the protease inhibitor levels in the body, but on the other hand, the protease inhibitors may have a major effect on Viagra. Drugs that strongly inhibit CYP3A4, including ritonavir, will sharply retard Viagra's breakdown. Persons taking ritonavir and other such drugs (nelfinavir also inhibits CYP3A4) should first try Viagra at 25 mg instead of the usual 50 mg. Future doses can be adjusted upward based on an individual's experience with efficacy and side effects (headache, facial flushing, digestive upset and impairments in color vision are the most common).

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