Disagreement among drug compendia on inclusion and ratings of drug-drug interactions

Objective: The aim of this study was to determine whether there is consistency in the listing and clinical significance ratings of drug-drug interactions in 5 nationally recognized drug information sources. Background: The Omnibus Budget Reconciliation Act of 1990, which established the Medicaid Drug Utilization Review (DUR) Program, required that the program assess data based on "explicit predetermined standards" including drug-drug interactions and other data specified in the statute. These standards, according to the statute, were to be based on 3 drug compendia and the peer-reviewed literature. This focus on explicit standards, plus a requirement that OUR screening criteria be in the public domain, has provided an opportunity to assess these criteria and the adequacy of the information on which they are based. Methods: We compared the listing and clinical significance ratings of drug-drug interactions for a representative sample of angiotensin-converting enzyme inhibitors, beta-blockers, benzodiazepines, calcium channel blockers, and nonsteroidal antiinflammatory drugs presented in US Pharmacopeia Drug Information, American Hospital Formulary Service Drug Information, Hansten's Drug Interactions Analysis and Management, Drug Interaction Facts (Facts and Comparisons), and the Micromedex DRUG-REAX(R) system. Results: In all the drug classes studied, individual drug-drug or drug-class interactions were rarely listed in greater than or equal to 1 or 2 drug information sources,Furthermore when particular drug-drug or drug-class interactions were listed in greater than or equal to 2 of the information sources reviewed, agreement on clinical significance rating generally decreased as the number of information sources in which the interaction was listed increased. Conclusions: Results of the study suggest that there are discrepancies in the listing and clinical significance ratings for drug-drug interactions among the leading drug information sources, although the reasons for these discrepancies could not be determined. The study findings also suggest the need to develop methods for resolving discrepancies based on review of the scientific evidence to ensure that DUR is based on high-quality screening criteria.