The Effects of Adherence to Non-Steroidal Anti-Inflammatory Drugs and Factors Influencing Drug Adherence in Patients with Knee Osteoarthritis.

We aimed to compare the clinical outcomes of knee osteoarthritis patients according to drug adherence; and to find out the factors the affecting those outcomes. We analyzed the drug adherence and clinical outcomes in 1,334 primary knee osteoarthritis patients who took non-steroidal anti-inflammatory drugs (NSAIDs) for 3 weeks. Clinical outcomes of Pain Numeric Rating Scale (NRS), Knee injury and Osteoarthritis Outcome Score (KOOS) and EQ-5D were compared at baseline and 3 weeks' follow-up between the two groups of adherent group and non-adherent group (1,167 vs. 167 patients). Logistic regression analysis was performed to examine the factors affecting the adherence, and the reasons for the non-adherence were asked. The follow-up clinical outcomes of NRS and KOOS symptom, pain and activity of daily life were significantly higher in the adherence group (P = 0.003, P = 0.048, P = 0.005, and P = 0.003, respectively). The adherence was better in the elderly and in the male group (P = 0.042 and P = 0.034, respectively) and the top reason for no strict adherence was "symptom improved" (21.5%) followed by side effects. In this study, the patients with better adherence to NSAIDs showed better outcomes compared to those with poor adherence. This study can contribute to the patient education for the pharmacological treatment in knee OA patients.