Effect of limonene on the in vitro permeation of nicardipine hydrochloride across the excised rat abdominal skin.

The aim of the present investigation was to study the effect of limonene on in vitro permeation of nicardipine hydrochloride across the excised rat abdominal skin from a 2% w/w hydroxypropyl cellulose (HPC) gel. The HPC gel formulations containing 1% w/w of nicardipine hydrochloride and selected concentrations of limonene (0% w/w to 12% w/w) were prepared, and subjected to in vitro permeation of the drug through excised rat abdominal epidermis. The drug content in the gels was found to be uniform and the drug was found to be stable in the HPC gel formulations. The permeation flux of nicardipine hydrochloride across rat epidermis was increased markedly by the addition of limonene to the HPC gels. A maximum flux was observed (246 +/- 1 micrograms/cm2/h) with an enhancement ratio of about 8 when limonene was incorporated at a concentration of 4% w/w. However, there was no further increase in the permeability of nicardipine hydrochloride beyond 4% w/w of limonene. The DSC and FT-IR data indicated that limonene increased the permeability of nicardipine hydrochloride across the rat epidermis by partial extraction of lipids in the stratum corneum. The results suggest that limonene may be useful for enhancing the skin permeability of nicardipine hydrochloride from transdermal therapeutic system containing HPC gel as a reservoir.