ObjectivePotentially fatal pulmonary toxicity is a dreaded complication of bleomycin. Increased use of granulocyte colony-stimulating factor in patients receiving chemotherapy has been paralleled by an increased incidence of bleomycin-induced pulmonary toxicity. We investigated whether granulocyte colony-stimulating factor (25 &mgr;g·kg−1·day−1, 4 days) enhanced endotracheal bleomycin-induced (5 mg/kg) acute lung injury and fibrosis in rats.SettingUniversity laboratory.SubjectsSprague-Dawley rats.InterventionsWe compared the effects of alveolar instillation of bleomycin in rats treated with either granulocyte colony-stimulating factor or saline.Measurements and Main ResultsMortality was 25% with bleomycin only and 50% with bleomycin + granulocyte colony-stimulating factor. Granulocyte colony-stimulating factor increased alveolar neutrophil recruitment, pulmonary edema, and lung myeloperoxidase activity on day 4. Lung static compliance on day 15 was severely decreased with bleomycin alone and showed a further significant decrease when granulocyte colony-stimulating factor was added (controls, 3.85 ± 0.14 mL/kPa; bleomycin, 1.44 ± 0.06 mL/kPa; and bleomycin + granulocyte colony-stimulating factor, 0.65 ± 0.09 mL/kPa; control vs. bleomycin,p< .0001; and bleomycin vs. bleomycin + granulocyte colony-stimulating factor,p= .0003). Lung morphology with bleomycin + granulocyte colony-stimulating factor showed, in addition to the changes observed with bleomycin alone, four patterns indicating more severe disease: honeycomb foci, pleural thickening with hyaline fibrosis, interstitial granuloma with increased number of macrophages but not neutrophils, and established interstitial fibrosis. Lidocaine, which prevents neutrophil adhesion to endothelial cells, inhibited granulocyte colony-stimulating factor-related exacerbation of acute lung injury (bronchoalveolar lavage fluid cells and pulmonary edema) and pulmonary fibrosis (lung static compliance and morphologic changes).ConclusionsGranulocyte colony-stimulating factor enhances bleomycin-induced lung toxicity by a mechanism that probably involves neutrophils.