VIAGRA: New Warning with Protease Inhibitors
VIAGRAŽ (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 apparently does not 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 half an hour to four hours before intercourse; physicians often start with 50 mg and then lower or raise the dose if needed. But 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 several 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 considerably less cautious than the Pfizer backgrounder quoted above. The backgrounder is conservative because discussions with the FDA are ongoing, and it is not known what the final recommendations will be. Technical information will be posted by the National AIDS Treatment Advocay Project, www.natap.org.]
The labeling also warns that anyone with an erection lasting more than four hours needs medical assistance immediately, because of the risk of tissue damage to the penis which could cause permanent loss of potency.
VIAGRA and Poppers
VIAGRA must not be combined with nitrite inhalants ("poppers") or any form of nitrates, because the combination may result in dangerously low blood pressure, which could be fatal.
