Efficacy of duloxetine in patients with knee osteoarthritis or chronic low back pain with early pain reduction: An exploratory post-hoc analysis of Japanese phase 3, 1-year extension studies

BACKGROUND Two previous phase 3, double-blind, randomized, placebo-controlled trials showed that duloxetine 60 mg/day for 14 weeks significantly improved pain and quality of life in Japanese patients with knee osteoarthritis or chronic low back pain. In their open-label extension studies, these improvements were maintained for ≥48 weeks. This post-hoc analysis assessed the relationship between initial response to duloxetine and long-term pain reduction and quality of life in patients with knee osteoarthritis or chronic low back pain. METHODS Patients (knee osteoarthritis: N = 43; chronic low back pain: N = 41) were subdivided based on extent of pain reduction from baseline to Week 4 of duloxetine (≥30%, 10-30%, or \u003c10% reduction in Brief Pain Inventory-Severity average pain score). Outcome measures were changes from baseline for Brief Pain Inventory-Severity and Brief Pain Inventory-Interference at regular intervals up to Week 65. RESULTS Mean change from baseline in Brief Pain Inventory-Severity was greater in patients with ≥30% early pain reduction than in patients with \u003c10% early pain reduction through Week 27 for both conditions, and also Weeks 47-65 for back pain. Compared with the \u003c10% early pain reduction group, mean change from baseline in the average of seven Brief Pain Inventory-Interference domain scores was greater in the ≥30% or 10-30% early pain reduction groups for knee osteoarthritis (except Weeks 63-65), and in the ≥30% early pain reduction group for chronic low back pain through Week 19. CONCLUSIONS These results suggest that patients with knee osteoarthritis who respond well to duloxetine in the first month might experience sustained, long-term pain relief with generally greater quality-of-life improvement than patients with poor initial response. Patients with chronic low back pain who had strong initial response may experience a greater long-term pain relief, but not greater quality-of-life improvement, than patients with poor initial response.