Study of a complexation process between naltrexone and Eudragit(R) L as an oral controlled release system

Polymeric complexes based on the interaction between Eudragit(R) L and naltrexone hydrochloride were elaborated. 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 naltrexone; (b) the determination of the aqueous solubility of naltrexone hydrochloride; and (c) the characterization of naltrexone hydrochloride from the following points of view: morphological (scanning electronic microscopy, SEM), thermal (differential scanning calorimetry, DSC and hot stage-microscopy, HSM) and spectroscopical (H-1- and C-13-nuclear magnetic resonance, NMR). Furthermore, some of these thechniques were used for the physical and chemical characterization of naltrexone polymeric complexes. An interaction by means of hydrogen bonds between the polymer and naltrexone was demonstrated using NMR spectroscopic techniques. The in vitro release of naltrexone-Eudragit(R) L complex using a pH gradient technique was studied. A significant reduction in the release rate of drug from the complex used as naltrexone controlled release system as well as a very high efficiency in the dissolution process have been found. (C) 1997 Elsevier Science B.V.