Nifedipine Users Endangered by Some Antibiotics: Which Ones?

(CBS) Antiobiotics save lives, but they also pose risks - including some that doctors may fail to recognize.

Case in point: The popular antibiotics erythromycin and clarithromycin can trigger dangerously low blood pressure (hypotension) when taken by people who already take nifedipine or another so-called calcium-channel blocker.

That's the key finding of a new study published in the Canadian Medical Association Journal.

For patients on a calcium-channel blocker who also need an antibiotic, azithromycin might be a safer bet, Dr. David Juurlink, head of the division of clinical pharmacology at the University of Toronto, told CBS News. Juurlink is the study's senior author.

The scientists examined hospitalization rates for hypotension or shock among elderly people. They found a heightened rate among patients who had been taking a calcium-channel blocker along with erythromycin or clarithromycin - but not with azithromycin.

In addition to nifidepine, calcium channel blockers include verapamil, diltiazem, amlodipine, and felodipine. The drugs are commonly used to treat high blood pressure.

What if you're taking a calcium-channel blocker and a doctor prescribes erythromycin or clarithromycin? Dr. Jrrulink recommends asking him/her if the combination is safe for you.

Said Juurlink, "It's the right thing to do."