Release, Uptake, and Permeation Behavior of Salicylic Acid in Ointment Bases

Abstract

In vitro release of salicylic acid from ointments was investigated by a diffusion technique employing a silicone rubber membrane. The advantages of this membrane over a cellophane membrane are discussed. Release of salicylic acid from five ointment bases indicated that emulsion-type ointment bases are superior to oleaginous and polyethylene glycol ointment bases. Uptake of salicylic acid by polyethylene glycol ointment from the solution was much faster than that by others, indicating a fairly strong affinity of this drug for the polyethylene glycol base. The permeation of salicylic acid from the aqueous solution through ointment bases to another aqueous solution was studied with a three-compartment diffusion cell to examine the relative importance of the factors involved in the process. Dimethyl sulfoxide and dimethylacetamide facilitated the release of salicylic acid from the ointments. Di-n-butylpropionamide was found to increase both the release of salicylic acid from the ointment and permeation through the ointment base. The in dim release pattern from various bases is in agreement with the in vivo data reported in the literature.