Polymyxin B sulfate modification of bacterial endotoxin: effects on the development of endotoxin shock in dogs.

The effects of endotoxin (lipopolysaccharide [LPS]) on the pathogenesis of canine endotoxin shock were compared with those of LPS which had interacted with polymyxin B sulfate prior to administration. Both LPS and polymyxin B-modified LPS caused comparable early decreases in aortic blood pressure, leukocyte and platelet numbers, and serum complement levels. However, in dogs receiving polymyxin B-modified LPS the late hypotensive phase was significantly ameliorated and lethality was significantly decreased. These data indicate that polymyxin B-modified LPS, though significantly less lethal than unmodified LPS, was capable of major interactions with several components of the humoral defense system, and support the concept that such interactions are not determinative in the pathogenesis of canine endotoxin shock.