Common Heart Drugs May Hamper Blood Thinner

Oct. 28 -- MONDAY, Oct. 27 (HealthDay News) -- Calcium channel blocker drugs, which are widely prescribed for coronary conditions, might reduce the effect of the clot-preventing drug Plavix, a new study says.

Calcium channel blockers appear to inactivate an enzyme essential for the activity of Plavix, said the report by Austrian physicians published online Oct. 28 in the Journal of the American College of Cardiology.

Studying 200 people who were taking Plavix after artery-opening procedures and stent placement, the University of Vienna researchers found a higher level of activity of platelets -- the blood cells that can clump together to form blood clots -- in those also taking calcium channel blockers.

"Moreover, intake of calcium channel blockers was associated with adverse clinical outcome," the researchers wrote.

Is the report something that doctors and people taking Plavix should worry about?

"We don't know," said Dr. Neal S. Kleiman, director of the cardiac catheterization laboratory at the Methodist DeBakey Heart and Vascular Center in Houston. He wrote an accompanying editorial in the journal.

"Is it possible that it is clinically significant? Yes, it is," Kleiman said. "Is it a test-tube finding that doesn't mean much? That is possible, too."

Those questions can be answered by analyzing studies containing information about people taking both drugs, Kleiman said. "There are many studies that have large databases that can be queried," he said. "There are ways to query them and see if there is an increased risk of stent thrombosis in patients taking calcium channel blockers."

Plavix (clopidogrel) is recommended for anyone having a stent implanted, to reduce the incidence of thrombosis, which is blockage of the reopened artery. One problem for the working cardiologist is that people who have stents -- wire mesh tubes -- implanted usually are taking a number of other drugs, often including calcium channel blockers, Kleiman said. Calcium channel blockers are commonly prescribed for high blood pressure and the chest pain called angina, he noted.