Objective: To assess changes in concurrent use of products containing terfenadine and contraindicated macrolide antibiotics (erythromycin, clarithromycin, troleandomycin) and imidazole antifungals (ketoconazole, itraconazole) following reports of serious drug-drug interactions and changes in product labeling.
Design: Retrospective review of computerized pharmacy claims.
Setting: A large health insurer in New England.
Patients: Health plan members with 1 or more paid pharmacy claims for products containing terfenadine between January 1990 and June 1994.
Main outcome measures: Among persons with paid claims for terfenadine in any given month, percentage with a prescription for any contraindicated drug that alternatively was dispensed on the same day as ("same-day dispensing") or had therapy days that overlapped those of ("overlapping use") a prescription for terfenadine.
Results: Concurrent use of terfenadine and contraindicated drugs declined over the study period. The rate of same-day dispensing declined by 84% from an average of 2.5 per 100 persons receiving terfenadine in 1990 to 0.4 per 100 persons during the first 6 months of 1994, while the rate of overlapping use declined by 57% (from 5.4 to 2.3 per 100 persons). Most cases involved erythromycin.
Conclusions: Despite substantial declines following reports of serious drug-drug interactions and changes in product labeling, concurrent use of terfenadine and contraindicated macrolide antibiotics and imidazole antifungals continues to occur.