Lung damage in mice from cyclophosphamide and thoracic irradiation: the effect of timing.

The development of lung damage in mice following thoracic irradiation is enhanced by cyclophosphamide (CY). CY was given at various times from 28 days before to 28 days after irradiation. Although increased damage was seen at all times, the extent showed marked variation according to the time interval. The most marked variations were seen when CY was given within 24 hours of irradiation; maximal enhancement was seen when CY was given before or with irradiation and minimal response when given 12 hrs before or 12 hrs after irradiation. It may therefore be prudent for the clinician to avoid such close time intervals between cytotoxic drugs and irradiation, unless a specific time-related therapeutic gain can be exploited.