The radioprotective effect of misonidazole (Ro-07-0582) on normal canine rectum

A single 1500 rad (=15 Gy) dose of 10-MeV X-rays was administered to the pelvis of 20 mongrel dogs. Ten received misonidazole (Ro-07-0582), 100 mg/kg p.o., 4 hours pre-irradiation. Serum misonidazole levels immediately pre-irradiation were 43 +/- 10 microgram/ml (mean +/- SD). The dogs were euthanized within 3 months post-irradiation. Each rectal specimen was studied for anatomic and histologic pathology and was assigned a Pathologic Alteration Score (PAS) of 1.2, or 3 in order of increasing severity. The PAS of the rectal specimens from the drug group was 1.6 +/- 0.7, and that of the controls 2.3 +/- 0.8. The PAS of the drug group was significantly lower than the control group (P = 0.008). The data suggest that misonidazole is a radioprotector for normal tissue.