Effects of thermal neutron irradiation on some potential excipients for colonic delivery systems

Different excipients, which are currently being studied for colon delivery systems, were examined with respect to their stability toward neutron irrad iation as a potential method of radiolabeling the formulations for gamma-sc intigraphic studies. Three different pectin and four different hydroxypropy l methylcellulose (HPMC) types, in addition to two types of polymethacrylat e films, were exposed to 1, 2, and 3 min of thermal neutron irradiation in a flux of 1.1 X 10(13) n cm(-2) s(-1). The physicochemical characteristics of pectins and HPMCs and the mechanical properties of the polymethacrylate films were examined after the radioactivity of the samples had declined to background levels. Methods included ultraviolet (UV) and Fourier transform infrared (FTIR) spectroscopy, pH measurements, loss on drying, thermogravim etric analysis (TGA), viscosimetry, gas chromatographic (GC) analysis of pe ctin monosaccharides, and tensile strength testing of the films. The result s suggest that pectins and HPMCs undergo degradation, as expressed by a sig nificant reduction in the dynamic and intrinsic viscosities of the samples. Generally HPMCs were more sensitive than pectins to neutron irradiation. H owever, calcium pectinate proved to be the most sensitive among all the inv estigated polymers. Both polymethacrylate films (Eudragit(R) L and S) resis ted loss of mechanical properties following 1 and 2 min of neutron irradiat ion, whereas irradiation for 3 min implied significant changes in the appea rance and the mechanical properties of Eudragit L films. As a conclusion, n eutron irradiation results in dose-dependent degradation of the investigate d polysaccharides and polymethacrylates. The consequences on the in vitro b ehavior of a formulation containing such polymers are discussed.