Drug interactions among commonly used medications. Chart simplifies data from critical literature review

To simplify risk assessment, we have developed a way to present critically appraised drug interaction information through a chart. Fifty drugs most frequently prescribed by Canadian family physicians and 16 drugs and substances that frequently interact with these drugs were the basis for a literature review. Drug interaction textbooks and MEDLINE (from 1966 to 1994) were searched for documented interactions. Reports of additive effects and animal or in vitro studies were excluded. All reports of interactions were evaluated for clinical effect, clinical significance, and quality of evidence. Of the 464 drug-drug or drug-substance pairs evaluated, 387 (83.4%) demonstrated an interaction, 59 (12.7%) documented no effect, and 18 (3.9%) pairs had conflicting evidence. Five percent of interactions were of major clinical significance; only 1.3% were of major clinical significance and supported by good-quality evidence. By using symbols, colours, and legends in a "grid-map" format, a large amount of drug interaction information was reduced to a single-page chart suitable for a desk reference or wall mounting. Our chart organizes a large amount of drug interaction information in a format that allows for rapid appreciation of outcome, clinical significance, and quality of evidence.