Efficacy and Safety of Diclofenac plus Capsaicin Gel in Patients with Acute Back/Neck Pain: A Multicenter Randomized Controlled Study

Introduction Back and neck pain are common musculoskeletal disorders. Topical non-steroidal anti-inflammatory drugs (NSAIDs) are frequently used to reduce pain and inflammation with fewer systemic side effects and drug interactions compared with oral NSAIDs. This study assessed efficacy and tolerability of a topical combination of capsaicin + diclofenac to treat acute back/neck pain. Methods In a randomized, double-blind, controlled, multicenter, parallel group trial, 746 patients were treated twice-daily for 5 days with diclofenac 2% + capsaicin 0.075%, diclofenac 2%, capsaicin 0.075% or placebo. Efficacy assessments included change and area under the curve in pain on movement for the worst procedure (POMWP), change in pressure algometry, and number of patients with decrease in POMWP of >= 30% and >= 50%. Adverse events (AEs) were recorded. Results Change in POMWP between baseline and day 2 evening, 1 h after drug application, demonstrates superiority of the combination (- 3.05 cm) versus diclofenac alone (- 2.33 cm) and placebo (- 2.45 cm), but not capsaicin alone (- 3.26 cm). AEs were consistent with known safety profiles. Conclusion Capsaicin alone and capsaicin + diclofenac showed superior benefit compared with placebo. However, diclofenac alone demonstrated efficacy comparable with placebo, and therefore its addition to capsaicin added no increased pain relief over capsaicin alone.