Bleomycins are a family of compounds produced by Streptomyces verticillis. They 
have potent tumour killing properties which have given them an important place 
in cancer chemotherapy. They cause little marrow suppression, but pulmonary 
toxicity is a major adverse effect. The mechanisms of cell toxicity are well 
described based on in vitro experiments on DNA. The bleomycin molecule has two 
main structural components: a bithiazole component which partially intercalates 
into the DNA helix, parting the strands, as well as pyrimidine and imidazole 
structures, which bind iron and oxygen forming an activated complex capable of 
releasing damaging oxidants in close proximity to the polynucleotide chains of 
DNA. This may lead to chain scission or structural modifications leading to 
release of free bases or their propenal derivatives. The mechanisms are well 
described based on in vitro experiments on DNA, but how they relate to intact 
cells in whole animals is more tenuous. Bleomycin is able to cause cell damage 
independent from its effect on DNA by induction lipid peroxidation. This may be 
particularly important in the lung and in part account for its ability to cause 
alveolar cell damage and subsequent pulmonary inflammation. The lung injury seen 
following bleomycin comprises an interstitial oedema with an influx of 
inflammatory and immune cells. This may lead to the development of pulmonary 
fibrosis, characterized by enhanced production and deposition of collagen and 
other matrix components. Several polypeptide mediators capable of stimulating 
fibroblasts replication or excessive collagen deposition have been implicated in 
this, but the precise role of these in bleomycin-induced fibrosis is yet to be 
demonstrated. Current therapy for bleomycin-induced lung damage is inadequate, 
with corticosteroids most often used. Given the mechanism of action described 
above, antioxidants and iron chelators might be beneficial. Although, studies to 
date are equivocal and there is insufficient evidence to promote their use 
clinically. Novel drugs are currently being developed and it is hoped these may 
be more useful.