A study of correlations between the release of drugs from petrolatum‐based gels containing nonionic surfactants and some physical and physico‐chemical characteristics of the gel systems

The in vitro release of benzocaine and 2‐ethyIhexyl p‐di‐methylaminobenzoate (EH‐PABA) from petrolatum‐based gels either containing two nonionic surfactants, or not, was compared with some physical and/or physico‐chemical characteristics of the drugs, the gels and the drug‐gel systems. The surfactants had no effect on the release of EH‐PABA, the less polar drug, whereas they decreased the release of benzocaine. Moreover, the release data show a complex dependence of diffusive properties of ben‐zocaine on drug and surfactant concentration. Benzocaine appears to form mixed micelles with each of the two surfactants and/or undergoes self‐aggregation phenomena within surfactant micelles. The results indicate that drug diffusion is influenced by gel porosity, drug molecular size and polarity and molecular interactions.