Transdermal absorption of L-dopa from hydrogel in rats.

To improve compliance in administration of l-dopa, transdermal absorption of the agent was investigated in rats in vitro employing two-chamber diffusion cells in which the excised rat abdominal skin was mounted, and in vivo using an alcoholic hydrogel containing l-menthol. The in vitro study revealed that in presence of l-menthol (2%, W/W), ethanol (20 and 40%, V/V) accelerated transdermal penetration of l-dopa with an increase of its percentages. The in vivo study showed that when the l-dopa-hydrogel containing 2% l-menthol and 40% ethanol was attached on the skin, plasma levels of l-dopa and norepinephrine increased with the time elapsed; the level of dopamine increased and reached a plateau thereafter; and the level of epinephrine was unchanged. These in vitro and in vivo findings indicated that the hydrogel formulation of l-dopa provides new direction in treating Parkinson's disease.