American doctors have been warned to stop prescribing the calcium-channel blocker nifedipine, used to treat high blood pressure, angina and heart attack.

The US National Heart, Lung and Blood Institute has warned physicians that short-acting nifedipine "should be used with great caution, if at all".

The warning is based on the study of 16 placebo-controlled clinical trials of short-acting nifedipine involving 8,350 heart patients. The risk of dying increased with the dosage; the mortality risk is one times greater than the average with dosages of between 30 and 50mg a day, increasing to nearly three times when the daily dose is 80 mg.

Another study the Institute considered showed that patients on calcium-channel blockers were 60 per cent more likely to suffer a heart attack than those taking either diuretics or beta-blockers.

Nifedipine was found to be the most dangerous of the three calcium-channel blockers, which also includes diltiazem and verapamil. The discovery, to be published next month by the Journal of the American Geriatrics Society, shows that the risk of dying was highest with nifedipine, while there was no risk associated with verapamil.

The Institute is still considering whether to extend the warning to other calcium-channel blockers. It points out that no significant risk has been proven in using diuretics and beta-blockers (The Lancet, September 16, 1995).