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Possible interactions with terfenadine or astemizole
A D Zechnich1, J R Hedges, D Eiselt-Proteau
1Department of Emergency Medicine, Oregon Health Sciences University School of Medicine, Portland 97201-3098.
The Western Journal of Medicine
|April 1, 1994
Summary
Concurrent prescribing of terfenadine/astemizole with erythromycin/ketoconazole risks fatal heart arrhythmias. Pharmacist screening can significantly reduce these dangerous drug interactions, improving patient safety.
Area of Science:
- Clinical Pharmacology
- Drug Interactions
- Cardiovascular Safety
Background:
- Concurrent use of terfenadine or astemizole with erythromycin or ketoconazole is associated with QT interval prolongation and potentially fatal ventricular arrhythmias.
- Understanding the frequency and patterns of such concurrent prescribing is crucial for mitigating serious drug interactions.
Purpose of the Study:
- To examine the frequency and patterns of concurrent prescribing of terfenadine or astemizole with macrolide antibiotics or ketoconazole.
- To suggest methods for reducing the incidence of these serious drug interactions.
Main Methods:
- Retrospective review of Oregon Medicaid prescription claims data spanning 22 months (1991-1992).
- Analysis of concurrent prescribing events involving terfenadine/astemizole and macrolide antibiotics/ketoconazole.
Main Results:
- Concurrent use episodes increased more than threefold from 1991 to 1992, with 122 total events identified.
- Most concurrent use (94%) involved terfenadine; 48% of patients received prescriptions from different physicians.
- Terfenadine use showed a 29% increase and a seasonal peak, indicating widespread and rising exposure.
Conclusions:
- Widespread and increasing use of terfenadine elevates the risk of serious drug interactions, often without physician awareness.
- Prospective pharmacist screening presents an effective strategy to significantly reduce concurrent prescribing incidents.
- Physicians need heightened awareness of these interactions to prevent co-prescription and manage related cardiac events.