Evaluation of the reliability and validity of a measure of anxiolytic drug-use intensity for pharmacoepidemiologic studies

OBJECTIVE: To assess the reliability and validity of a proposed new standard of drug-use intensity, the minimum marketed dose (MMD), using anxiolytic drugs as models. DESIGN: Retrospective, cohort design. SETTING: Staff model, nonprofit health maintenance organization. PATIENTS/PARTICIPANTS: Eighty-five patients who obtained one or more prescriptions for an anxiolytic, antidepressant, or sedative-hypnotic drug during three consecutive one-year time periods. Fifty-nine patients had a prescription filled during the year before the study. RESULTS: For anxiolytic drugs, the magnitude of the average correlation for the MMD measure of drug-use intensity was greater than the total number of prescriptions and the total number of dosage units. Discriminant validity was demonstrated because the MMD was not correlated with measures in unrelated therapeutic categories. Summed MMD units were shown to significantly predict physical impairment (criterion validity). CONCLUSIONS: The MMD measure of drug-use intensity was reliable and valid for anxiolytic drugs. These findings suggest that information gathered from automated prescription records may be a useful indicator of drug-use intensity in pharmacoepidemiologic studies.