Comparison of Safety Outcomes of Topical Capsaicin-Loaded Niosome and Capsaicin Gel in Healthy Volunteers

Capsaicin is a crucial molecule from chili that is approved by the Thai FDA for relieving joint and muscle pain. However, skin irritation causes 40% of patients to withdraw from treatment. To assess the effect of the niosome formulation on reducing side effects, this prospective study compared the safety outcomes of 0.025% capsaicin-loaded niosome (CLN), capsaicin-gel (CG), and placebo in 75 healthy volunteers. The physicochemical characteristics of CLN formulation were evaluated before applying to volunteers. CLN exhibits an average vesicle size of 246.70 nm with 238.06 ± 11.26 µg/mL of capsaicin. CG is a commercial product. Capsaicin formulations were blindly administered to the upper arm of the volunteers three times a day at 4-hour intervals. The safety outcomes were measured by skin erythema and melanin content using a colorimeter and pain score before and after application at times 0, 4, 8, and 24 hours after the first administration for the skin before application (baseline), and placebo. CLN significantly increased skin erythema with scores of 8.39 ± 1.88 and 6.46 ± 2.15 when applied at 0 and 4 hours. In contrast, CG achieved significant increases for all 3 times of applications, with scores of 9.87 ± 2.08, 7.99 ± 2.32, and 6.78 ± 1.47 when applied at 0, 4, and 8 hours respectively. CG treatment significantly increased erythema scores after 24 hours compared to the baseline and placebo (P<0.01), while CLN had no effect. CG and CLN showed a significant increase in pain after 24 hours when compared to the baseline (P<0.05). The study suggests that CLN could be safer for the capsaicin-loaded formulation, causing less irritation and potentially reducing melanin content.