EXTENDED INVITRO RELEASE STUDIES OF SALICYLIC-ACID AND HYDROCORTISONE FROM PETROLATUM OINTMENT BASES

Ointment bases comprising of homogenous mixtures of petrolatum with 6, 12 and 18% w/w liquid paraffin and containing 4% w/w salicylic acid or hydrocortisone as model drugs were formulated. Viscosity measurements were taken in the linear viscoelastic range by applying normal pressure on plugs made of the oinment bases. Viscosity of the bases influenced the release of drug by affecting drug diffusivity. Both in the case of salicylic acid and hydrocortisone, the cumulative amount of drug released increased with a decrease in the viscosity of the base. The Higuchi model for the prediction of drug release from suspension-type ointment bases was followed during the initial period (up to 36 h). At later stages, the cumulative amount of drug released had a non-linear relationship to the square-root of time. A good correlation was obtained between the reciprocal of viscosity of the base and the initial release rate or total amount of drug released after 240 h.