Protection of mouse lung by WR-2721 after fractionated doses of irradiation.

The radioprotective effect of WR-2721 on mouse lung has been studied after single doses, 4 or 7 equal fractions of X rays. Using breathing rate and lethality to measure lung injury up to 1 year after radiation, significant protection against both pneumonitis at 7 months and fibrosis at 12 months was observed using 300 mg/kg of WR-2721. The degree of radioprotection was similar for pneumonitis and fibrosis and was not less after doses per fraction of 4.0 Gy. These data indicate that protection of mouse lung by WR-2721 will not be less in a multifractionated schedule of radiation, at least for doses per fraction greater than 4.0 Gy.