Eudragit RS-PM and Ethocel 100 Premium: influence over the behavior of didanosine inert matrix system

Inert matrices of didanosine (ddI) were elaborated as controlled release dosage forms, using two different types of polymers: Eudragit RS-PM, an anionic acrylic acid copolymer, and Ethocel 100 Premium, an ethylcellulose. A preformulation study of the drug was designed to address the following points: (a) the development of two alternative methods (high performance liquid chromatography (HPLC) and UV spectrophotometry) for the analysis and quantifying of ddI; (b) the determination of the aqueous solubility of ddI; and (c) the characterization of ddI from the following points of view: morphological (scanning electronic microscopy (SEM)) and thermal (differential scanning calorimetry (DSC)). Furthermore, some of these techniques were used for the characterization of those components which will be included in the oral controlled release system to be developed. The in vitro release of ddI matrices was studied at pH 7.4, because of the instability of ddI at pH values lower than 3 units. A significant reduction in the release rate of drug from both ddI controlled release systems was found. Furthermore, Ethocel 100 Premium showed a minor efficiency in the dissolution process, with a reduction of more than double in the final dissolution efficiency (DE) value. This parameter and the fit factors (f1 and f2) have been compared for the characterization of dissolution profiles.