Relationship Between Pain Reduction and Improvement in Health-Related Quality of Life in Patients with Knee Pain Due to Osteoarthritis Receiving Duloxetine: Exploratory Post Hoc Analysis of a Japanese Phase 3 Randomized Study

PURPOSE: This post hoc analysis of a Japanese phase 3 randomized study (ClinicalTrials.gov identifier: NCT02248480) investigated relationships between changes in pain severity and changes in health-related quality of life (HRQoL) in duloxetine-treated patients with knee osteoarthritis (OA). PATIENTS AND METHODS: Patients with knee OA and Brief Pain Inventory (BPI) average pain score ≥4 received duloxetine 60 mg/day or placebo for 14 weeks. Spearman rank correlation coefficients were calculated for change in pain severity, as assessed by the BPI, and change in HRQoL, as assessed by the items of the (i) 36-item Short-Form Health Survey (SF-36; a generic measure of HRQoL) and (ii) Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC; an OA-specific measure of HRQoL). RESULTS: After 14 weeks of treatment, there was a significantly greater improvement (p<0.001) for duloxetine (n=177) vs placebo (n=176) in BPI average pain severity score and significantly greater improvements (p<0.01) for duloxetine vs placebo for 5 of the 8 SF-36 domains (including the Role-Physical, Bodily Pain, and Physical Functioning domains) and all 24 individual WOMAC items. The correlation between BPI change from baseline and SF-36 item change from baseline was statistically significant (p<0.05) for 2 of the 8 SF-36 items (Bodily Pain, Physical Functioning) in duloxetine-treated patients. The correlation between BPI change from baseline and WOMAC item change from baseline was statistically significant for 22 of the 24 WOMAC items in duloxetine-treated patients. CONCLUSION: This post hoc analysis suggested that the pain reduction observed in duloxetine-treated patients with knee OA was associated with improvements in OA-specific aspects of HRQoL, ie, pain and physical functioning.