Stereoselective hydrolysis and penetration of propranolol prodrugs: in vitro evaluation using hairless mouse skin.

Stereoselective hydrolysis of two ester prodrugs of propranolol, isovaleryl propranolol (IV-PL) and cyclopropanoyl propranolol (CP-PL), was studied in Tris-HCl buffer (pH 7.4) containing 0.15 M KCl, skin and liver homogenates, 5% plasma in Tris-HCl buffer, skin cytosol and microsomes, and liver cytosol and microsomes. The hydrolysis rate constants of (R)-isomers of the prodrugs were 1.1-30.3 times greater than those of the respective (S)-isomers in tissue preparations. Skin showed considerable metabolic activity and very high stereoselectivity (R/S ratio: 7.3-30.3). The hydrolyzing capacities of buffer and different tissue preparations per milligram of protein content were in the following increasing order: buffer < skin homogenate < plasma < liver homogenate. The studies with microsomes and cytosol indicated that the esterases, which are responsible for the hydrolysis of prodrugs, were mainly present in the cytosolic and microsomal fractions of skin and liver, respectively. There was a good correlation between the octanol-buffer partition coefficients of propranolol and its prodrugs and the skin partition coefficient. In vitro stereoselective penetration of propranolol and the prodrugs through full-thickness hairless mouse skin was evaluated with flow-through diffusion cells.(ABSTRACT TRUNCATED AT 250 WORDS)