Patients who took erythromycin with inhibitors of CYP3A drug enzymes including certain calcium-channel blockers, anti-fungal drugs, and anti-depressants had a five-fold greater risk of sudden cardiac death than patients who did not take the drugs at the same time, according to an article in the September 9th issue of the New England Journal of Medicine.

In the study, Wayne A. Ray, Ph.D., and his American colleagues did not find the same increased risk for patients who took CYP3A inhibitors with other antibiotics, such as amoxicillin, or for those who had taken erythromycin in the past. The study was part of a national program to increase awareness of the benefits and risks of new, existing, or combined uses of therapeutic drugs and devices.

"This study provides critical scientific evidence that can be used to improve health care quality and safety by preventing potentially dangerous drug interactions," said Carolyn M. Clancy, M.D, who is associated with the national initiative as a whole. "These findings will help clinicians to make more informed choices about which antibiotics should be used with patients who are taking multiple medications."

In the current work, researchers reviewed medical records for the one state’s healthcare system and identified patients who had sudden cardiac deaths between January 1, 1988 and December 31, 1993. They reviewed prescriptions for erythromycin, amoxicillin, and other medications from computerized pharmacy files that included the drug, dose, and total medication dispensed. Behavioral risk factors, such as smoking and a lack of physical activity, were not studied.

Researchers concluded that clinicians should avoid prescribing a combination of erythromycin and CYP3A inhibitors to patients at the same time because there are safer, effective alternatives.