Possible risks of combining calcium-channel blockers and antibiotics

Monday brought word, first reported in the Canadian Medical Association Journal, of possible risks for patients simultaneously taking calcium channel blockers and erythromycin (E-Mycin) or clarithromycin (Biaxin) — both macrolide antibiotics. Calcium channel blockers are widely prescribed blood pressure medications. Among the drugs in this family are amlodipine (Norvasc), felodipine (Plendil), nifedipine (Procardia, Adalat) and diltiazem (Cardizem, Dilacor, Tiazac).

The macrolides are the most commonly prescribed antibiotics.

The study, which examined 999,000 patients in the province of Ontario treated with calcium channel blockers between 1994 and 2009, found that patients who received erythromycin were six times as likely to suffer a sudden bout of low blood pressure requiring hospitalization. Patients who took clarithromycin and calcium channel blockers were four times as likely to suffer low blood pressure requiring hospitalization. No effect was seen among patients taking azithromycin, a related antibiotic in the same class which goes by the trade name Zithromax.

ACSH's Dr. Gilbert Ross comments, “The study suggests that patients over age 60 may be more sensitive to these effects. Given these results, a physician treating an older patient on a calcium channel blocker who requires an antibiotic should probably first consider a non-macrolide antibiotic, and then, if necessary, should look to azithromycin.”