Drug interactions in primary health care. A retrospective database study and its implications for the design of a computerized decision support system.

OBJECTIVE: To investigate the occurrence of potential drug interactions in primary health care from the perspective of the prescribing general practitioner.
DESIGN: Retrospective database study of computer-based patient records with a query language. All drug prescriptions during a four year period were compared with concurrent or overlapping prescriptions for the same patient and these drug pairs were compared with a database of drug interactions from the Swedish drug catalogue.
SETTING: One health centre in Sweden with six general practitioners and two doctors on vocational training. PARTICIPANTS: All patients who had visited a doctor at the health centre between 1 November 1986 and 31 October 1990. MAIN OUTCOME MEASURES: The rate of potential interactions in relation to all drug prescriptions and the incidence rate of potential interactions for patients at risk (those receiving two or more drugs).
RESULTS: Approximately 55,000 drug prescriptions were analysed for potential drug interactions. A total of 1,074 cases of potential drug interactions were found, which corresponds to a rate of 1.9% of all drug prescriptions. The incidence rate of potential interactions was 12% for all patients at risk (those receiving two or more drugs) and 22% for elderly (> = 65 years of age) patients at risk. Major interactions were investigated concerning the extent to which the prescribing doctors were aware of the potential interactions.
CONCLUSION: Potential drug interactions occur at a high rate in general practice, in particular for elderly patients. Properly designed computer-based decision-support might increase the prescribing doctor's awareness of clinically significant interactions and improve the quality of drug treatment.