Coprescription of Terfenadine and Erythromycin or Ketaconazole: an Assessment of Potential Harm

Purpose: In a retrospective study, the authors used a pharmacy claims database to analyze the rate of coprescription of terfenadine and erythromycin or ketaconazole.

Study Period: The investigators reviewed claims filed for these drugs between January 1, 1990, and June 30, 1993. The time period allowed for comparison of coprescription rates before and after the Food and Drug Administration (FDA) required the manufacturer of terfenadine to inform the medical community of potentially serious adverse interactions.

Results: There were 5,802 coprescription events for terfenadine and erythromycin and 150 coprescription events for terfenadine and ketaconazole. Rates per 100,000 terfenadine users demonstrated large declines about 18 months after initial regulatory action. Coprescription events of terfenadine with either erythromycin or ketaconazole continued to occur despite regulatory action.

Conclusions: Results of this study suggest important roles for the pharmacist as a risk manager, disseminating information about newly published drug interactions. Both health providers and patients are audiences for the pharmacist's drug expertise. The delay in physician reaction to new information from pharmaceutical companies and the federal government suggests an early, strong role for the pharmacist in changing prescribing behavior.