Methods: Data were pooled from 3 double-blind, randomized, placebo-controlled, 12-week trials in DPNP patients without major mood disorders. Study 1 (N=457) compared duloxetine 20mg once daily (QD), 60mg QD, 60mg twice daily (BID), and placebo; Studies 2 (N=334) and 3 (N=348) compared duloxetine 60mg QD and 60mg BID with placebo. DPNP patients reporting somnolence or on sedating concomitant medications (n=216) were dropped. Efficacy measures included average daily and night pain severity, both collected via patient diaries, and the Brief Pain Inventory (BPI) interference items. National or institutional review boards at each study site approved the protocols and all patients provided signed informed consent prior to study participation.

Results: Weekly mean scores of daily and night pain severity were calculated for Weeks 1-12. BPI was administered at Weeks 4, 8, and 12. At baseline, both daily and night pain severity were positively and significantly correlated with sleep interference (r=0.37 and 0.57, respectively; p<.001). Both duloxetine doses were significantly superior to placebo in reducing daily and night pain at Week 1 and at all assessment times thereafter. Both duloxetine doses were superior to placebo in reducing sleep interference at Weeks 4, 8, and 12. Correlations between changes to endpoint in daily and night pain with sleep interference changes were 0.48 and 0.54 for all patients and 0.46 and 0.53 for non-somnolent/nonsedating medication patients, respectively (p<.001).

Conclusions: Results suggest moderate to strong associations at baseline between daily pain, night pain and sleep interference, as well as between changes in pain (daily and night) and changes in sleep interference. Although causality was not established, findings suggest improvements in pain will be associated with less sleep interference.