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Mode of action:


Inhibition of cell membrane function. Disrupt the structure of cell membrane phospholipids and increase cell permeability by a detergent-like action, causing cell death.  This binding is competitive with calcium and magnesium. Polymixins have also been shown to neutralize endotoxins.



Polymixin B, colistin (Polymixin E)



Bacillus polymyxa

Spectrum of activity:

Narrow spectrum affecting primarily Gram negative bacteria


Effect on bacteria:



Examples of applications in Veterinary Medicine:

Cattle: colibacillosis and salmonellosis in calves, mastitis

Swine: neonatal porcine colibacillosis

Horses: bacterial keratitis or metritis caused by Klebsiella spp.

Dogs and cats: bacterial keratitis, otitis externa, skin infections




Polymixins are not absorbed from the gastrointestinal tract.  Because of their excessive nephrotoxic nature, other polymixin classes have been discarded.




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