A randomized, double-blind, placebo-controlled study on the efficacy and safety of 50% and 75% capsaicin ointment as compared to a topical local anesthetic cream (eutectic mixture of lidocaine 2.5% and prilocaine 2.5%) as a topical anesthetic agent

ABSTRACT

BACKGROUND: Capsicum frutescens or 'siling labuyo' is known for its nutritional and pharmacological properties. Its most potent and predominant chemical entity is capsaicin. A recent study on rabbits concluded that 'siling labuyo' fruit extract is comparable to a topical local anesthetic medication containing lidocaine and prilocaine as an anesthetic agent.OBJECTIVES: This study aimed to determine the efficacy and safety of capsaicin ointment as a topical anesthetic agent in comparison with a topical local anesthetic cream (eutectic mixture of lidocaine and prilocaine) and placebo ointment in healthy human volunteers.METHODS: A patch test was done prior to clinical testing. Thirty (30) healthy adult volunteers were enrolled. Irritation potential of 50% and 75% ointments were determined. On the clinical trial phase, 85 patients were included. The following test drugs were used 50% capsaicin ointment, 75% capsaicin ointment, eutectic mixture of 2.5% lidocaine and 2.5% prilocaine, and placebo ointment. Allocation of the test drugs to the marked boxes on the patient's forearm was done through simple randomization using a computer-generated random allocation scheme. Both the subjects and the investigators were blinded on the test drugs applied. Test ointments and placebo were applied on the marked areas of the forearms and occluded with a transparent plastic film. After 60 minutes, the investigator recorded any adverse reactions. The marked areas were then tested for pain sensation using a needle lever apparatus that enabled the sharp point of the needle to thrust uniformly and perpendicularly on the marked test areas. The subjects were asked to assess the pain by a verbal response scale for pain. Adverse reactions were again noted on the 24th and 72nd hour.RESULTS: In the patch test, the primary irritation index (PII) scores of both 50% and 75% ointments (0.05 and 0.18), were classified as non-irritant and probably safe for intact human skin contact.In the clinical trial phase, the data were analyzed using Wilcoxon signed ranks test. It established that the positive control (cream containing eutectic mixture of lidocaine and prilocaine) had significantly lower pain scores than 50% and 75% capsaicin ointments and placebo. Capsaicin ointments were no better than placebo in terms of mean pain scores.CONCLUSION: In humans, 50% and 75% capsaicin ointments are not effective as a topical anesthetic agent as compared to the eutectic mixture of lidocaine and prilocaine. Capsaicin ointment is associated with mild adverse reactions which were described as stinging and itching sensations which were seen in 84.7% of patients.