Demographic, medical, and behavioral characteristics associated with over the counter non-steroidal anti-inflammatory drug use in a population-based cohort: results from the Multi-Ethnic Study of Atherosclerosis

Background Three types of non-steroidal anti-inflammatory drugs (NSAIDs) can be obtained both over the counter (OTC) and by prescription in the United States. OTC NSAID use is not recorded in prescription claims databases; this might lead to differential misclassification of NSAID exposure status in studies that use computerized pharmacy databases to study NSAID use. Objective To evaluate characteristics of OTC versus prescription NSAID users. Methods This analysis is set within the Multi-Ethnic Study of Atherosclerosis (MESA) study; a prospective cohort study of 6814 adults from four ethnic groups (European descent, Asian, African-American, and Hispanic) with a mean age of 62 years. The cohort was restricted to those who initiated NSAID use (aspirin, ibuprofen, or naproxen) during follow-up. We compared information about age, sex, ethnicity, body mass index, smoking, diabetes, medication use, education, income, health insurance status, and exercise between groups. Results OTC NSAID use was prevalent at baseline (25% aspirin, 9% ibuprofen, and 2% naproxen). Compared to prescribed NSAID use, OTC NSAID use was lower for users of non-European descent for all classes: aspirin (p<0.0001), ibuprofen (p<0.0001), and naproxen (p = 0.0094). For aspirin, differences were seen for male gender (relative risk (RR): 0.92; 95% confidence interval (CI): 0.86-0.98), use of lipid lowering drugs (RR: 0.88; 95% CI: 0.80-0.96), low income (RR: 0.89; 95% CI: 0.81-0.97), and participants one standard deviation above average in intentional exercise (RR: 1.03; 95% CI: 1.01-1.05). Conclusions OTC NSAID use is prevalent in an older multi-ethnic population and OTC users differ from prescription NSAID users. Caution should be exercised when using prescribed NSAIDs as a proxy for NSAID use. Copyright (C) 2010 John Wiley & Sons, Ltd.