Post-irradiation treatment with OK432 can prevent radiation-induced bone marrow death.

The radioprotective effect of OK432, a Streptococcus haemolyticus preparation, on bone marrow death was examined in mice. The LD50 value was increased from 7.55 Gy in controls to 8.45 Gy in mice treated once with OK432 immediately after irradiation. Multiple administrations of the agent further elevated the LD50 value to 9.56 Gy. The radioprotective effect was also apparent when multiple treatments were commenced as late as 72 h after irradiation.