Tolerability of NGX-4010, a capsaicin 8% patch, in conjunction with three topical anesthetic formulations for the treatment of neuropathic pain

Lynn R Webster¹, John F Peppin², Frederick T Murphy^3,4, Jeffrey K Tobias⁵, Geertrui F Vanhove^5
1Lifetree Clinical Research and Pain Clinic, Lifetree Medical Inc, Salt Lake City, UT, USA; ²Clinical Research Division, The Pain Treatment Center of the Bluegrass, Lexington, KY, USA; ³Altoona Center for Clinical Research, Duncansville, PA, USA; ⁴University of Pennsylvania, School of Medicine, Philadelphia, PA, USA; ⁵NeurogesX Inc, San Mateo, CA, USA

Background: The objective of this study was to assess the safety, tolerability, and preliminary efficacy of NGX-4010, a capsaicin 8% patch, following pretreatment with three different topical anesthetics in patients with peripheral neuropathic pain.
Methods: This open-label, multicenter study enrolled 117 patients with post-herpetic neuralgia, HIV-associated distal sensory polyneuropathy, or painful diabetic neuropathy. Patients received pretreatment with one of three lidocaine 4%-based topical anesthetics (L.M.X.4^® [Ferndale Laboratories Inc, Ferndale, MI], Topicaine^® Gel [Estela Basso, Jupiter, FL], or Betacaine Enhanced Gel 4 [Tiberius Inc, Tampa, FL]) for 60 minutes followed by a single 60- or 90-minute NGX-4010 application, and were followed for 12 weeks. Tolerability and safety measures included “pain now” Numeric Pain Rating Scale (NPRS) scores, dermal assessments, medication use for treatment-related pain, adverse events (AEs), clinical laboratory parameters, physical examinations, and vital signs. The primary efficacy variable was the percentage change in mean NPRS scores for “average pain for the past 24 hours” from baseline to weeks 2 through 12.
Results: Treatment with NGX-4010 following pretreatment with any of the three topical anesthetics was generally safe and well tolerated. Nearly all patients completed ≥90% of the planned NGX-4010 application duration. The most common treatment-related AEs, application-site burning and application-site pain, were transient, mostly mild or moderate, and could be adequately managed by local cooling or short-acting oral opioid analgesics. Although slightly more patients used medication for treatment-related discomfort following pretreatment with Topicaine compared with L.M.X.4 or Betacaine, there were no statistical differences between the topical anesthetics. Neuropathic pain reduction from baseline to weeks 2 through 12 was approximately 30% and was similar among the topical anesthetics; the proportion of responders ranged from 45% to 50%.
Conclusion: Treatment with NGX-4010 following pretreatment with any of the three topical anesthetics was generally safe and well tolerated; no significant differences in the parameters measured were noted between the pretreatment groups.

Keywords: neuropathic pain, capsaicin patch, tolerability, topical anesthetics