Topical lidocaine patch 5% may target a novel underlying pain mechanism in osteoarthritis

SUMMARY

Recent literature and animal research has provided insight to potentially new analgesic targets for managing osteoarthritis (OA) pain. Primary afferent neurons located in affected joints express excessive amounts of abnormally functioning sodium (Na) channels on their surface in response to the inflammatory process. These Na channels may play an integral role in production of pain and hyperalgesia. Hence, the authors set out to conduct a 2-week, open-label, multicenter proof-of-concept study to evaluate the effectiveness and safety of lidocaine patch 5% monotherapy in adults with OA pain of the knee ( n = 20). Patients with OA of one or both knees who were experiencing inadequate pain relief (defined as an average daily pain intensity of > 4 on a 0 to 10 pain scale) with their current analgesic regimen (i.e. APAP, NSAIDs, COX-2 inhibitors, tramadol) were enrolled and had all analgesic medications discontinued. Treatment with the lidocaine patch 5% resulted in significant improvements in the Western Ontario and McMaster Universities OA Index (WOMAC) pain, stiffness, physical function subscales and composite index (48.4, 41.1, 47.0, and 46.8% improvements respectively, p < 0.01). In addition, significant improvement was noted for pain intensity, pain relief, and pain interference with quality of life as measured by the Brief Pain Inventory ( p < 0.05). The lidocaine patch 5% was generally well tolerated and no patients discontinued due to treatment-related adverse events. Given the open-label design, lack of a control group, and small sample size, the findings from our pilot study need to be confirmed by larger randomized controlled trials. Topical lidocaine patch 5% may provide clinicians with a novel, non-systemic therapy for OA pain with a unique mechanism of action.

Key words: :

• Clinical trials
• Osteoarthritis
• Pain
• Topical analgesics
• WOMAC