Dissolving microneedles for enhanced local delivery of capsaicin to rat skin tissue

Capsaicin-loaded dissolving microneedles (DMNs) were prepared to investigate the analgesic effect of capsaicin on the skin. The dimensions of each microneedle (MN) were as follows: diameter of the basement, 17?mm; length, 500?μm; and width, 300?μm. The average capsaicin content in the DMNs loaded with a low and high dose of capsaicin was 8.8?±?0.5?mg and 12.5?±?0.4?mg. Almost all the capsaicin, 99.3?±?4.1% and 99.7?±?2.2% for low-dose and high-dose DMNs were released within 20?min. High amounts of capsaicin were recovered with 102.8?±?0.1% of capsaicin after storage at 23?°C for 90 days. The pharmacological activity of capsaicin DMNs was compared to that of capsaicin cream as a positive control, by measuring the idiospasm of depilated rat skin. The time required to achieve 50% idiospasm suppression was 26.3?±?1.9?min and 53.0?±?2.3?min for low-dose and high-dose DMNs. A pharmacokinetic study showed high tissue capsaicin levels of 660.2?±?120.6 and 1805.3?±?218.1?μg/g wet weight for low-dose and high-dose DMNs at 5?min after administration. The results suggest that DMNs could exert a rapid local analgesic action on the skin.