A study of 750 people with high blood pressure by teams in the United States and Italy has suggested that those who were taking calcium channel blockers were twice as likely to develop cancer as those taking other anti-hypertensive drugs.
The findings are the latest in a series which have raised questions about the long-term safety of calcium channel blockers, which include the world's second best-selling drug, Adalat (nifedipine).
American researchers last year said that patients taking such drugs had a 60 per cent greater risk of heart attack than people on cheaper alternatives such as beta-blockers.
The news sent share prices of some pharmaceutical companies plummeting, and called into question their marketing methods. Calcium channel blockers are believed to have gained their market position through a combination of positive marketing and over- emphasis on the side-effects of rival medication.
Following the heart attack study doctors in Britain began rethinking their strategy for treating high blood pressure, which affects 25 per cent of adults in the country - about 14 million people - and is a lucrative market.
Then another study published in the Lancet journal earlier this year suggested that calcium channel blockers caused increased gastrointestinal bleeding in elderly patients. Now the new findings, published in the current issue of the American Journal of Hypertension, have uncovered a possible link with cancer.
In a group of 202 elderly patients on three different calcium channel blockers there were 27 cancers, 13 more than would be expected, according to scientists from the National Institute on Aging in Maryland and the Catholic University in Rome.
A US cancer specialist, Janet Daling of the Fred Hutchinson Cancer Research Center in Seattle, says there is a "biologically plausible" explanation for the role of the drugs in cancer development. They are known to inhibit the death of cells and could, in theory, allow cancerous cells to persist in the body.
Doctors here said yesterday that the safety of calcium channel blockers was an "issue" but definitive answers would not be forthcoming until an Anglo-Scandinavian clinical trial reports in six years time. They urged patients taking calcium channel blockers, such as nifedipine, verapamil and diltiazem, not to panic, and to continue with their medication.
Gareth Beevers, president of the British Hypertensive Society, professor of medicine at Birmingham University School of Medicine, said: "The American/Italian findings are interesting but they do not constitute proof of anything. We need proper randomised, controlled clinical trials. Until then we should treat these claims from retrospective trials which are subject to biases with tremendous caution."
Professor Beevers said that the cancers reported in the elderly patients were a "mixed bag ... If they had all been one type, such as leukaemias, then I might feel differently." Calls by some US doctors for a ban on the use of the drugs for treating high blood pressure were "premature", he added.
Dr Graham Leighton, head of medical affairs at Bayer which makes the drug Adalat, said that the drug had been used in 90,000 patients worldwide over 20 years and there was no evidence of any problems.
He said the new study was in too small a group of patients to be significant, and that the earlier studies linking calcium channel blockers with heart attacks and bleeding, had been disputed by other independent researchers. "Our first concern is to make sure that patients are not put at risk, and that they don't come off their drugs on the basis of questionable findings," he said.Reuse content