High Concentration Capsaicin Patch in Neuropathic Pain: A Systematic Review and Meta-Analysis of Randomized Control Trials
Post-herpetic neuralgia, diabetic peripheral neuropathy, and HIV-associated polyneuropathy are common causes of focal neuropathic pain. Therapeutic options for treating focal neuropathic pain remain inconsistent. When compared to oral medications, topical agents are attractive as they may be able to limit systemic side effects with dose escalation. The purpose of this study is to determine the efficacy and safety of NGX-4010 (a high-concentration capsaicin patch) compared to low dose or pooled controlled patch.
Materials and Methods:
A search was performed on Ovid MEDLINE® 1946 to Present. The results were downloaded into EndNote X7, a bibliographic database manager, and the duplicates were removed. To retrieve appropriate articles, the keywords capsaicin and neuropath* (truncated to include other suffixes) were used. Clinical randomized controlled trials involving human studies receiving a single application of the high-concentration 8% capsaicin patch for the treatment of neuropathic pain with 12-week follow-ups were considered for inclusion in this review. An Ovid Medline search was conducted on January 18, 2017 to include studies with a keyword search of “capsaicin” and “neuropath” between 1946 until the search date. Two independent reviewers (J.E. and K.S.) evaluated 913 studies and discrepancies were resolved through discussion and consensus between the two authors. The study selection strategy is shown in Figure 1.
Seven RCTs with 1910 participants were included in the meta-analysis. For the primary outcome (number of patients with >30% reduction in pain score), seven trials with 884 in the placebo arm and 1026 in the high concentration capsaicin arm reported a significantly higher odds of positive response to reduction in pain for the high concentration capsaicin group compared to placebo (OR 1.43, 95% CI: 1.19 to 1.73, P<0.0001). There was no evidence of heterogeneity in the primary outcome (P=0.822, I2 = 0.0%). Secondary outcome measures included mean change in pain score, follow up pain score, and adverse effect. Analysis of five studies revealed that the mean change in pain score favored use of the high concentration capsaicin patch compared to control (mean difference -0.35, 95% CI -0.54 to -0.15, P<0.0001). Five studies reported the mean pain score at final follow-up and no statistical difference was observed (mean difference 1.02, 95% CI -0.10 to 2.14, P=0.074). There were significantly higher rates of burning, dryness, and formation of vesicles with the use of high concentration capsaicin patch compared to control. Although not significant, the rate of pain, dryness and erythema was higher amongst the high concentration capsaicin group compared to control.
Discussion: Patients who received a high concentration capsaicin patch had higher odds of getting pain relief compared to the control group. There was a significant change in pain score from baseline amongst the high concentration capsaicin group, but the mean pain score was not significantly different at follow up. Despite these benefits, there was an increased rate of cutaneous side effects with the use of high concentration capsaicin patch compared to control. The high concentration capsaicin patch may have a role in the treatment of focal neuropathic pain conditions, but the side effect profile needs to be carefully discussed with patients before administration.