NEW YORK, Jul 20 (Reuters) -- Giving supplemental doses of vitamin C to heart disease patients who take nitrate drugs can ensure that the drugs remain effective over time, according to a study.
Drugs such as nitroglycerin dilate the blood vessels and improve blood flow to the heart. They are often prescribed for patients who have chest pain due to diseased coronary arteries.
But most nitrovasodilators "share the disadvantage of inducing nitrate tolerance, especially during nonintermittent administration," note the study's authors, a team of researchers led by Dr. Eberhard Bassenge of the University of Freiburg in Germany. When tolerance develops, patients do not respond well to the drugs. Eventually, patients have to switch to different medications, which often cause more side effects.
It is not clear why patients develop tolerance to nitrovasodilators. But some findings suggests that free radicals, destructive molecules that are the byproducts of various metabolic processes, play a role. Previous research suggests that the metabolism of nitrovasodilators produces relatively high levels of free radicals. Since vitamin C and other antioxidants have been found to inactivate free radicals, Bassenge and colleagues hypothesized that the vitamin might prevent tolerance.
To test this hypothesis, the researchers studied the effects of the drug glyceroltrinitrate (GTN) and vitamin C on 9 healthy volunteers. The researchers divided the volunteers into three groups. One group took 0.8 milligrams of GTN and 3,000 mg of vitamin C daily for 3 days. Another took GTN and a placebo daily for the same period of time. The third group took a placebo and vitamin C every day for 3 days. Over the course of the 3 days, the researchers studied changes in the volunteers' blood vessels.
Both groups taking GTN showed an initial response to the drug, the researchers report in the current issue of the Journal of Clinical Investigation. The volunteers' blood vessels dilated when they took the drug, the researchers found. But volunteers taking GTN and the placebo showed a decreased response to the drug over time, while those taking the drug and vitamin C continued to show a consistent response.
"In conclusion, we have shown that tolerance to nonintermittent GTN administration in humans can be circumvented by dietary supplementation with vitamin C," the authors write. These findings "suggest that administration of vitamin C may prove useful for overcoming the tolerant state induced during prolonged administration of nitrovasodilators," they conclude.
SOURCE: Journal of Clinical Investigation 1998;102:67-71.
