Supramicellar solutions of sodium dodecyl sulphate 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 nifedipine. Because this drug is practically insoluble in water, the in vitro release characteristics of the formulations were verified using different dissolution methods. A new sustained-release dosage form, formulated in two different strengths: 30 and 60 mg, was tested and compared to an extended- release commercial product. Initially, the dissolution tests were carried out with the paddle method, in a large amount of water (51), to maintain the 'sink conditions'. Then the release tests were repeated using aqueous solutions of sodium dodecyl sulphate (SDS) as dissolution fluid (in 51, first, and then in 11 of medium). Different supramicellar concentrations of the surfactant were used to verify how the different dissolution media could influence the release characteristics of the formulations proposed. The commercial product was tested in the same experimental conditions and was considered as reference dosage form. The results show that the surfactant concentrations 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 different percentages of SDS.