Viagra (sildenafil) doses must be low when the drug is used with HIV protease inhibitors (especially ritonavir), because these antiretrovirals reduce the metabolism of sildenafil in the liver, resulting in abnormally high blood levels which can cause adverse effects. The combination does not seem to affect blood levels of protease inhibitors.
Sildenafil, used to treat erectile dysfunction, is supplied as tablets in three doses: 25, 50, and 100 mg, and is taken 1/2 an hour to 4 hours before intercourse. Doctors often start with 50 mg, then lower or raise the dose if needed. According to an April 21 "Backgrounder for HIV Treatment Advocates" from Pfizer Inc., "Given the magnitude of the interaction between sildenafil and protease inhibitors, ongoing discussions with the FDA indicate that a maximum single dose of 25 mg of sildenafil in a 48 hour period should not be exceeded in patients receiving these agents concurrently."
There are other medications which require caution if used with sildenafil (and some which must not be combined at all). Patients should obtain this information from a medical professional, or from a recent copy of the official labeling of the drug. [Note: The current labeling, dated February 1999, is considerable less cautious than the Pfizer backgrounder quoted above. The back-grounder is conservative because discussions with the FDA are ongoing, and it is not known what the final recommendations will be. Information will be posted by the NATA Project, www.natap.org.]
Warning: Anyone with an erection lasting more than 4 hours needs medical assistance immediately, because of the risk of tissue damage which could cause permanent loss of potency.
Viagra must not be combined with nitrite inhalants ("poppers") or any form of nitrates. The combination may result in dangerously low blood pressure, which could be fatal.
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This article was provided by Women Alive. It is a part of the publication Women Alive Newsletter.