Systems approach to vaginal delivery of drugs V: in situ vaginal absorption of 1-alkanoic acids.

The vaginal absorption of a homologous series of ionizable compounds, the 1-alkanoic acids, was studied using a perfusion method with a rib-cage cell surgically implanted in the rabbit vagina. The absorption rates of these compounds followed first-order kinetics. The physical model previously used for the 1-alkanols, but accounting for the pKa and pH effects in the present case was employed in the analysis of the carboxylic acid data. The aqueous diffusion layer thickness was 0.031 cm. The permeability coefficient for the lipoidal pathway increased 3.5-fold per methylene group. Both values agree reasonably well with those obtained in the alcohol study.