Formulation for slow release of oral radiation-protection drugs

Cysteine and cysteamine, two effective radioprotectants in mammals, were compressed into tablets with a matrix composed of ethylcellulose and stearic acid at various proportions. The concentration of the unoxidized drug was monitored continuously for 8-16 h, as a parameter for the residual drug in the tablets with time, in vitro. Also, in vivo studies with tablets implanted into stomachs of rats, at various time intervals before their whole-body irradiation, were carried out. A correlation was obtained in the in vitro studies between the stearic acid/ethylcellulose ratio and the release rate of both radioprotectants, and the Higuchi's diffusional mechanism was demonstrated. In vivo, the best survival ratios were obtained when 8 h lapsed between implantation of the tablets in the stomachs and the irradiation. It is concluded that there is a distinct correlation between the in vitro release of the drugs and their in vivo efficacy as radioprotectants.