Prevalence of potential proton-pump inhibitor drug interactions: a retrospective review of prescriptions in community pharmacies.

Drug interactions are a major cause of drug-related problems. This study assessed the comparative frequency of potential drug-drug interactions in patients receiving either omeprazole or lansoprazole. We reviewed prescription data from 144 community pharmacies in 25 states for the period of October 12, 1996, through October 20, 1997, from which the rates at which patients received either proton-pump inhibitor concurrently with > or =1 potentially interacting drugs were determined. A total of 7306 patients received only omeprazole, and 2486 received only lansoprazole. In this sample, 722 patients (9.9%) who received omeprazole also received a potentially interacting medication at the same time, compared with 8 patients (0.3%) who received lansoprazole (P<0.001). These data suggest that clinicians should be conscientious when selecting or dispensing drugs for patients taking omeprazole, given the relatively high prevalence of potential drug interactions in clinical practice.