The Relationship between Polypharmacy and Physical Activity in Those with or at Risk of Knee Osteoarthritis.

OBJECTIVES: Physical activity is associated with improved pain, functional status, and less disability in persons with knee osteoarthritis (KOA). Because polypharmacy is related to several adverse health outcomes in older persons, we hypothesized that it might also be associated with decreased physical activity in those with KOA. This study evaluates the relationship between the number of prescription medications and weekly moderate to vigorous physical activity (MVPA). DESIGN: We used hierarchical median quantile regression analysis to examine the cross-sectional association between the number of prescription medications taken in the past 30 days and the median objectively measured MVPA minutes controlling for demographic and clinical variables. SETTING: Four Osteoarthritis Initiative (OAI) recruitment centers in Providence, Rhode Island; Columbus, Ohio; Baltimore, Maryland; and Pittsburgh, Pennsylvania. PARTICIPANTS: Accelerometer monitoring occurred in 2,127 OAI participants. Of these, 1,889 participants had 4 or more days of valid physical activity monitoring data and complete medication/covariate data. Data were collected at the 48-month OAI follow-up visit (2008-2010). MEASUREMENTS: The outcome was weekly minutes of MVPA measured with an accelerometer. Number/type of prescribed medications and covariate data (age, sex, race/ethnicity, body mass index, presence of comorbidities, pain, depressive symptoms, and radiographic KOA severity) were taken from the public OAI database. Polypharmacy was defined as taking five or more prescribed medications. RESULTS: The prevalence of polypharmacy in the study population was 28.2%. Each additional prescription medication was related to a decrease of 3.6 minutes (95% confidence interval [CI] = -4.8 to -2.1) in median weekly MVPA minutes. Participants meeting the polypharmacy criterion exhibited a decrease of 12.6 minutes (95% CI = -21.2 to -4.7) in median weekly MVPA minutes compared with those not meeting the criterion. CONCLUSION: An increased number of prescription medications and polypharmacy are associated cross-sectionally with decreased MVPA in adults with KOA. Further study is necessary to establish the causal nature of this association.