Transdermal delivery of nicardipine: an approach to in vitro permeation enhancement.

Nicardipine hydrochloride (NC-HCl), a calcium channel blocker for the treatment of chronic stable angina and hypertension, seems to be a potential therapeutic transdermal system candidate, mainly due to its low dose, short half-life, and high first-pass metabolism. The objective of the present study was to evaluate its flux and elucidate mechanistic effects of formulation components on transdermal permeation of the drug through the skin. Solubility of NC-HCl in different solvent systems was determined using a validated HPLC method. The solubility of drug in various solvent systems was found to be in decreasing order as propylene glycol (PG)/oleic acid (OA)/dimethyl isosorbide (DMI) (80:10:10 v/v) > PG > PG/OA (90:10 v/v) > polyethylene glycol 300 > ethanol/PG (70:30 w/w) > transcutol > dimethyl isosorbide (DMI) > ethanol > water and buffer 4.7 > 2-propanol. Propylene glycol was then selected as the main vehicle in the development of a transdermal product. As a preliminary step to develop a transdermal delivery system, vehicle effect on the percutaneous absorption of NC-HCl was determined using the excised skin of a hairless guinea pig. Vehicles investigated included pure solvents alone and their selected blends, chosen based on the solubility results. In vitro permeation data were collected at 37 degrees C, using Franz diffusion cells. The skin permeation was then evaluated by measuring the steady state permeation rate (flux) of NC-HCl, lag time, and the permeability constant. The results showed that no individual solvent was capable of promoting NC-HCl penetration. Permeation profiles of the drug through hairless guinea pig skin using saturated solutions of drug were constructed. Among the systems studied, the ternary mixture of PG/OA/DMI and binary mixture of PG/OA showed excellent flux. The flux value of the ternary system was nearly three times higher than the corresponding values obtained for the binary solvent. A similar trend also was observed for the permeation constant, while the values of lag time were reversed. The ternary mixture was then selected as a potential absorption enhancement vehicle for the transdermal delivery of drug. In general, higher fluxes were observed through hairless guinea pig skin as compared with the human stratum corneum. Based on the results obtained from the release study of NC-HCl from saturated solutions of the drug, a novel lecithin organogel (microemulsion-based gel) composed of soybean lecithin, propylene glycol, oleic acid, dimethyl isosorbide, and isopropyl myristate was developed as a possible matrix for transdermal delivery of NC-HCl. In vitro percutaneous penetration studies from this newly developed gel system through giunea pig skin and human stratum corneum revealed that the organogel system has skin-enhancing potential and could be a promising matrix for the transdermal delivery of nicardipine. Furthermore, higher permeation rates were observed when nicardipine free base was incorporated into the gel matrix instead of hydrochloride salt.