Prescription-acquired acetaminophen use and the risk of asthma in adults: a case-control study.

BACKGROUND: Studies have examined the association between acetaminophen use and asthma; however, their interpretation is limited by several methodologic issues. OBJECTIVE: To investigate the association between recent and chronic prescription-acquired acetaminophen use and asthma. METHODS: This retrospective case-control study used a 10% random sample of the IMS LifeLink commercial claims data from 1997 to 2009. Cases had to have at least 1 incident claim of asthma; 3:1 controls matched on age, sex, and region were randomly chosen. Acetaminophen exposure, dose, and duration were measured in the 7- and 30-day (recent) and the 1-year (chronic) look-back periods. Multivariable conditional logistic regression was used to estimate the risk of asthma associated with acetaminophen use adjusted for comorbidities, other drugs increasing asthma risk, and health system factors. RESULTS: There were 28,892 cases and 86,676 controls, with mean age of 42.8 years; 37.7% were males, and 22.6% of cases and 18.2% of controls had acetaminophen exposure in the pre-index year, with mean cumulative doses of 78.7 g and 59.8 g, respectively. There was no significant association between recent prescription acetaminophen exposure and asthma (7 days: OR 1.02, p = 0.74; 30 days: OR 0.97, p = 0.38). Cumulative prescription acetaminophen dose in the year prior increased asthma risk compared to acetaminophen nonusers (<= 1 kg: OR 1.09, p < 0.001 and > 1 kg: OR = 1.60, p = 0.02). Duration of prescription acetaminophen use greater than 30 days was associated with elevated asthma risk (OR 1.39, p < 0.001). CONCLUSIONS: Chronic prescription-acquired acetaminophen use was associated with an increased risk of asthma, while recent use was not. However, over-the-counter acetaminophen use was not captured in this study and further epidemiologic research with complete acetaminophen exposure ascertainment and research on pathophysiologic mechanisms is needed to confirm these relationships.