Enhanced skin permeation of a lipophilic drug using supersaturated formulations

Supersaturation was used to enhance the permeation of a lipophilic model compound (a lavendustin derivative, LAP) through excised pig skin in vitro. The drug was dissolved in a series of liquid and semisolid vehicles (in which it had different solubilities) and which were prepared using either (i) the method of mixed cosolvents, (ii) the method of solvent evaporation, or (iii) the method of dissolving the drug with heating. Saturated formulations showed comparable permeation rates through the skin, independent of the absolute concentration of the drug in the vehicle. Supersaturated solutions at a degree of saturation of two resulted in a doubling of the drug permeation rate. These experiments show, therefore, that the percutaneous absorption of LAP may be consistently increased using supersaturated formulations, independent of the type and composition of the vehicles and independent of their method of preparation.