Skin permeability of water-soluble drugs

The permeabilities of several water-soluble drugs through excised hairless rat skin from their aqueous suspensions were investigated by using newly designed two-chamber diffusion cells. Disodium cromoglycate, diclofenac sodium, dopamine hydrochloride, isoproterenol hydrochloride, diltiazem hydrochloride and papaverine hydrochloride were selected as water-soluble drugs. Indomethacin, a lipophilic drug, and deuterium oxide (D2O) were used for comparison. The skin permeability coefficients of these water-soluble drugs were 100--1000 times lower than that of indomethacin. Since these drugs have high solubility in the donor solution (distilled water or lactate buffer), however, the skin permeation rates, which are in general proportional to the product of skin permeability coefficient and solubility of drugs in the drug-donor compartment, were comparable to or higher than that of indomethacin (1.7 micrograms/cm2/h): the skin permeation rate of dopamine hydrochloride (458 micrograms/cm2/h) was about 300 times higher than that of indomethacin. The water-soluble drugs with lower molecular weight and higher solubility in water showed higher skin permeation rates. These results suggest that some water-soluble drugs with low molecular weight and high solubility in water might be good candidates for transdermal drug delivery.