effect of cimetidine and famotidine on survival of lethally gamma irradiated mice

background: currently available radioprotectors are poorly tolerated in man and the general use of aminothiols is compromised by their side effects. this study was carried out to test and compare the radioprotective potential of cimetidine and famotidine against lethally gamma irradiated nmri mice. materials and methods: adult male nmri mice in groups of 10 were exposed to various doses of gamma rays at a dose rate of 93.3 cgy generated from a co- 60 source. mortality was examined daily for 30 days after irradiation. various doses of gamma rays were used to calculate ld50/30. different doses of cimetidine and famotidine were used in combination with 8 gy gamma rays to find out the optimum protecting concentration of either drug. finally the optimum protecting concentration of either drug was used in combination with various doses of gamma rays. each experiment was repeated for three times. results: results show that mean ld50/30 for radiation alone was found to be 723.7 cgy. when using different doses of cimetidine in combination with 801 cgy gamma rays, the dose of 15 mg/kg cimetidine produced optimum protection, while optimum dose of famotidine was found to be 10 mg/kg. however, ld50/30 obtained with optimum dose of either cimetidine or famotidine led to a drf of 1.11 and 1.05 respectively. conclusion: cimetidine compared to famotidine was found to be more protective against mortality induced by radiation in mice. this effect of cimetidine might be due to its immunomodulatory role and thus protecting bone marrow and lymphoid tissue injuries following whole body gamma irradiation.