Viagra cancels painkiller side effects, but might have side effects of its own


28 October 2005

The impotence drug Viagra could be used to block gastric inflammation caused by drugs such as aspirin and ibuprofen, report researchers.

Nonsteroidal anti-inflammatory drugs (NSAIDs), including aspirin, ibuprofen, and indomethacin, are effective against inflammation, but their clinical use is limited by potential gastric side effects, including stomach ulcers. Now, pre-clinical data from Brazil suggests that patients who would otherwise benefit from regular doses of NSAIDs could avoid the risk of gastric damage. 

NSAIDs prevent pain and inflammation by inhibiting the pro-inflammatory cyclooxygenase enzymes COX-1 and COX-2, which produce prostaglandins in the body. Prostaglandins are involved in a number of inflammatory processes. COX-1 disruption is thought to have a negative effect on the prostaglandin-regulated mucous lining of the gastrointestinal tract, while COX-2 inhibition provides pain relief.

Camila Santos and Marcellus Souza at the Federal University of Ceará, Brazil investigated whether Viagra (sildenafil) could protect the gastrointestinal tract in rats dosed with the NSAID indomethacin.   The indomethacin reduced gastric blood flow and increased the adhesion of inflammatory white blood cells, two possible precursors to gastric side effects. Sildenafil corrected both of these effects, possibly through its nitric oxide-generating properties. 

Since both sildenafil and NSAIDs are already licensed, human trials would progress rapidly, says Adriano Rossi from the MRC Centre for Inflammation Research at the University of Edinburgh.

Rossi welcomes the findings, but notes that this treatment to reduce one set of side effects might come with side effects of its own. 'Ideally the dose would be regulated such that it only had significant effects on the stomach,' Rossi told Chemistry World.  'However, side effects like unwanted erections are a possibility.'

Attempts to inhibit COX-2 alone with drugs such as the withdrawn NSAID Vioxx have not provided the solution (Chemistry World, March 2005, p10).   Meanwhile Viagra is currently in clinical trials for hypertension, and shows pre-clinical promise in heart attack, stroke, diabetes and congestive heart failure. Helen Carmichael

References

C L Santos et alBrit. J. Pharmacol., 2005, 146, 481

D A Sawatzky, I L Megson and A G Rossi, Brit. J. Pharmacol., 2005, 146, 477