In Vivo Assessment of a Capsaicin-Containing Microemulsion for Neuropathic Pain Management

Abstract

BACKGROUND/AIMS: Capsaicin (CAP) has been used in clinical applications for the treatment of neuropathic pain (NP). The main disadvantages of CAP are its short half-life, low water solubility and low bioavailability. This study intended to produce a therapeutically effective microemulsion (ME) formulation comprising CAP to decrease NP. MATERIALS AND METHODS: ME was prepared using oleic acid, Tween 80, propylene glycol, ethanol, and water. Neuropathy was induced by partial sciatic nerve ligation (PSL) in mice. Two weeks after, PSL NP was tested using the cold plate (CP) and von Frey (VF) tests. The mice in the treatment group were administered 10 mg/kg CAP by oral gavage. The effects on NP of conventional CAP and ME CAP were compared. RESULTS: The prepared ME formulation of (CAP) was a homogeneous, transparent, thermodynamically stable dispersion of water and oil. The classic CAP was not effective on NP, while ME CAP was effective in the CP. The ME CAP was more effective on mice, than classic CAP using the VF test. CONCLUSION: The developed novel ME formulation at lower doses could reduce side effects and improve the bioavailability of the oral administration of CAP in the treatment of NP, and thus, would achieve good patient compliance.