Objective: An increased number of drugs used by patients enhances the risk of potentially hazardous drug interactions. So far, no representative data are available about how common this problem is in German general practices.
Methods: We performed a retrospective analysis using a prescription database for a German region. The 50 general practitioners (out of 1,457) who wrote the most prescriptions during January to March 2003 were included. Data on 4,153 patients who were prescribed at least 10 drugs were analyzed for 92 predefined Drug Combinations Prone to Interact (DCPI) to a clinically relevant extent and possible contraindications.
Results: From 92 DCPIs, 71 occurred in the analyzed population between 1 and 275 times. The total number of DCPI cases was 1,295, which included 10% (n = 129) of contraindicated combinations. Among 4,153 analyzed patients, 822 patients (19.8%) were affected by at least 1 DCPI. In 268 patients (6.5%), multiple DCPIs occurred. The most frequently found drug pairs were digitalis/diuretics, digitalis/calcium channel blockers, and theophylline/quinolones. Among contraindicated combinations, tricyclic antidepressants, St. John's wort and antiarrhythmic drugs were most frequently involved. In about 1/3 of patients treated for chronic heart failure, pharmacotherapy appeared not to be guideline-adherent.
Conclusion: Drug interactions, especially in polypharmacotherapy, represent a potential hazard which must be taken into account by the prescribing physician. Our study is the first to use a prescription database for the evaluation of drug prescriptions within a German region.