SUPRAMICELLAR SOLUTIONS OF SODIUM DODECYL-SULFATE AS DISSOLUTION MEDIA TO STUDY THE IN-VITRO RELEASE CHARACTERISTICS OF SUSTAINED-RELEASE FORMULATIONS CONTAINING AN INSOLUBLE DRUG - NIFEDIPINE

.In this study we consider some different approaches to analyze the in vitro dissolution behaviour of different dosage forms containing nife dipine. Because this drug is practically insoluble in water, the in vi tro release characteristics of the formulations were verified using di fferent dissolution methods. A new sustained-release dosage form, form ulated in two different strengths: 30 and 60 mg, was tested and compar ed to an extended-release commercial product. Initially, the dissoluti on tests were carried out with the paddle method, in a large amount of water (5 1), to maintain the 'sink conditions'. Then the release test s were repeated using aqueous solutions of sodium dodecyl sulphate (SD S) as dissolution fluid (in 5 1, first, and then in 1 1 of medium). Di fferent supramicellar concentrations of the surfactant were used to ve rify how the different dissolution media could influence the release c haracteristics of the formulations proposed. The commercial product wa s tested in the same experimental conditions and was considered as ref erence dosage form. The results show that the surfactant concentration s above 0.50% are able to dissolve the drug content of all the dosage forms tested. Above this concentration, the dissolution profiles from the delivery systems considered are not affected by the presence of di fferent percentages of SDS.