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Efficacy and Safety of 0.625% and 1.25% Capsaicin Patch in Peripheral Neuropathic Pain: Multi-Center, Randomized, and Semi-Double Blind Controlled Study.

BACKGROUND
Topical capsaicin therapy may be of benefit in providing pain relief in patients with peripheral neuropathy.


OBJECTIVES
To investigate the efficacy and safety of 0.625% (50 µg/cm2) and 1.25% (100 µg/cm2) capsaicin patches (CPs) compared to conventional 0.075% capsaicin cream or placebo patches in patients suffering from peripheral neuropathy.


STUDY DESIGN
Early Phase II, multi-center, randomized, semi-double-blind, and placebo-controlled clinical trial.


SETTING
Two medical college teaching hospitals.


METHODS
Sixty patients were randomized to the 0.625% CP, 1.25% CP, placebo-controlled patch, or 0.075% capsaicin cream. The primary efficacy endpoint was the mean difference in the change of daily numerical rating scale (NRS) pain score. Secondary endpoints included values for the Daily Sleep Interference Scale, the percentage of patients achieving a >/= 30% or >/= 50% reduction in pain, and data for Global Impression Change (GIC) and EQ-5D.


RESULTS
Patients treated with the 0.625% CP and 0.075% capsaicin cream showed statistically significant improvements in pain after 6-weeks of test drug application. Daily sleep disorder scores were improved only for those patients applying the 0.075% capsaicin cream. For patient-derived GIC scores, the majority (11 of 12) of patients in the 0.625% CP group reported that their pain was improved. For the safety evaluation, 2 severe adverse events were reported for the 0.075% capsaicin cream group only. Repetitive patch application was related to minor skin problems such as a burning sensation, erythema, pruritus, and vesicles in 28 patients (46.67%).


LIMITATIONS
The small sample size and relatively high dropout rates.


CONCLUSIONS
Our data indicate that the 0.625% CP may prove to be an effective and safe alternative with which to treat patients with peripheral neuropathy and could replace the high concentration (8%) CP. Further studies are now needed to definitively establish efficacy.Key words: Capsaicin, patch, CP, topical capsaicin, neuropathic pain, peripheral neuropathic pain, PNP, high concentration CPTrial Registration: ClinicalTrials.gov, NCT02228928.