Clinical meaningfulness of duloxetine’s effect in Chinese patients with chronic pain due to osteoarthritis: post hoc analyses of a phase 3 randomized trial

PURPOSE: To evaluate the analgesic effect of duloxetine in Chinese patients with osteoarthritis (OA) of the knee/hip at individual patient level and report the relationship between pain intensity reduction, overall improvement, and physical functioning. PATIENTS AND METHODS: Post hoc analysis of 13-week, phase 3, parallel-group, randomized, placebo-controlled study of duloxetine in Chinese patients with OA pain. Patients were randomized (1:1, computer-generated, interactive web-response system) to duloxetine (60 mg once daily, n=202) or placebo (n=207). Patients, investigators, and study staff were blinded throughout the study. Duloxetine’s efficacy was evaluated using the Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials (IMMPACT) and the Osteoarthritis Research Society International and Outcome Measures in Rheumatology (OARSI-OMERACT) responder criteria. Analyses were conducted on all randomized patients with a baseline and at least one post-baseline observation. RESULTS: At study endpoint, the percentage of patients experiencing ≥30% pain intensity reduction (30% responders) was significantly higher in the duloxetine group than in the placebo group (63.4% vs 49.7%; P=0.008). The percentage of patients experiencing ≥50% pain intensity reduction (50% responders) in the duloxetine group was numerically higher than in the placebo group (42.8% vs 34.5%; P=0.098). Most of the 30% and 50% responders to duloxetine treatment felt either “very much improved” or “much improved” on the Patient Global Impression-Improvement at endpoint. The 30% and 50% responders to duloxetine treatment also experienced greater improvements in the Western Ontario and McMaster Universities Osteoarthritis Index physical function scores at endpoint compared with non-responders. The overall percentage of OARSI-OMERACT responders was significantly higher in the duloxetine group vs the placebo group (70.1% vs 54.9%; P=0.003). CONCLUSION: Based on IMMPACT and OARSI-OMERACT criteria, the analgesic effect of duloxetine was associated with clinically relevant benefits in Chinese patients with OA of the knee/hip. CLINICALTRIALS.GOV IDENTIFIER: NCT01931475.