Interaction risk with proton pump inhibitors in general practice: significant disagreement between different drug-related information sources

AIMS: To compare information on drug-drug interactions (DDIs) reported on two standard drug-related information sources (Summary of Product Characteristics and Drugdex system by Micromedex), by assessing the prevalence and predictors of potential DDI with proton pump inhibitors (PPIs) in general practice. METHODS: From the 'Caserta-1' Local Health-Service database, 156 general practitioners (GPs) were recruited. From more than 180,000 individuals registered on their lists, we selected patients receiving co-prescription of PPI and medications at interaction risk, according to the Italian Summary of Product Characteristics (SPC) of PPI and Drugdex information, during the year 2003. Thereafter, we carried out a regression analysis to identify the predictors of co-prescription at interaction risk with PPI, on the basis of the two information sources. A number of analyses were performed to evaluate agreement on DDI information between the SPC of PPI and Drugdex. RESULTS: According to SPC and Drugdex, 324 (3.0%) and 958 (9.0%) patients, respectively, received co-prescriptions of PPI and potentially interacting medications during the study period. PPI users' age, type of medication and number of other drug prescriptions per month were independent predictors of receiving co-prescriptions at interaction risk, when considering only Drugdex. With regard to potential DDIs with PPI, a significant disagreement (P < 0.0001) between the two drug-related information sources, was shown through agreement analyses. CONCLUSIONS: Potential DDIs with PPI are a common health issue in general practice. Estimates of prevalence and predictors of potential DDIs with PPI significantly changes according to the drug information source being used.