The influence of salicylic acid on the in vitro release of anthralin from an o/w cream.

A diffusion cell with an artificial membrane (dialysis membrane) was used to study the in vitro release of antralin from an o/w cream (Locobase) in the presence of salicylic acid. The concentration range of antralin was 0.04-3.0%. The influence of salicylic acid on the in vitro release was studied by adding 0.5-3.0% salicylic acid to the creams. Addition of salicylic acid improves the solubility of anthralin in water and probably also in the aqueous phase of the cream. It may also have an effect on the microviscosity of the cream as the structure of the cream changes. Both these factors promoted the in vitro release of antralin. There was also an improvement in clinical efficacy when salicylic acid was added. In this case, the results also can be explained by an isolated effect on the permeability of the stratum corneum.