Background:
The radiation damages could be repaired, but some of these damages which fail to repair could result in cell death or mutation. The induced damages could be modulated by radioprotectors. Cimetidine and famotidine belong to antagonists to the histamine H2 receptor which their efficacy in protection against radiation was studied, but, their effectiveness in oral administration and the combination of famotidine and cimetidine is not studied yet. The aim of this study was the assessment of combined effects of famotidine and cimetidine on irradiated mice survival.
 
Materials and Methods:
270 male NMRI mice were provided and divided into 11 major groups including sham control. Some of these groups were divided into more than one subgroup. The study groups were irradiated with the doses of 6, 7, 8, 9 Gy and were treated with the doses of 2, 4 and 8 mg/kg famotidine, 10, 20 and 40 mg/kg cimetidine and the combination of both. Then, their survival fractions, as percentages of mice who survived until 30 days, were measured.
 
Results:
The LD50/30 for radiation alone was determined as 7.47 Gy. By treating the mice with a concentration of 4 and 20 mg/kg for famotidine and cimetidine, respectively, the survival fraction of animals was significantly higher than the LD50/30 group. The combined regimen of famotidine+cimetidine in radioprotection had higher DRF than each of them, separately but this difference was not statistically significant. The DRF of combined, famotidine, and cimetidine groups were 1.09, 1.08, and 1.01 respectively.
 
Conclusions:
Our results are implying that the combined regimen of famotidine+cimetidine in radioprotection had not a significant higher DRF than each of them separately, and we did not find a synergic effect in combined oral famotidine and cimetidine on irradiated mice.