Simultaneous control of capsaicinoids release from polymeric nanocapsules.

The nanoencapsulation of capsaicinoids (capsaicin and dihydrocapsaicin) was proposed in this work as a strategy to control their release due to the reservoir characteristics of the nanocapsules. This reservoir property could prolong the topical analgesic effect and reduce the burning sensation and skin irritation caused by the capsaicinoids. The nanocapsules were physicochemically characterized and presented z-average diameter of 153 +/- 7 (PDI < 0.2) and zeta potential of +9.62 +/- 1.48 mV. The pH of the aqueous nanoparticle suspension was 5.72 +/- 0.10, which is suitable for cutaneous application. The total capsaicinoids content was 0.5 mg mL(-1) (64% of capsaicin and 33% of dihydrocapsaicin) and their encapsulation efficiencies were close to 100%. The formulation was stable over 90 days. The in vitro release profiles demonstrated that the release of capsaicin and dihydrocapsaicin was prolonged by means of nanoencapsulation. Moreover, comparing the half-life values, it was observed that the polymeric wall significantly affected the release rates for both capsaicinoids. According to Fick's first law, capsaicin presented higher flux (5.6 +/- 0.1 (x10(-4)) mg cm(-2) h(-1)) than that of dihydrocapsaicin (2.1 +/- 0.2 (x 10(-4)) mg cm(-2) h(-1)), which was probably related to its higher gradient concentration. Drug diffusion and polymer relaxation were responsible for the capsaicinoids release from the nanocapsules, which fitted the monoexponential mathematical model. This innovative formulation was designed considering its potential action of prolonging the analgesic effect of the capsaicionoids on the skin.