Polymyxin B was isolated by Wellcome Research Laboratories, in 1949, from the mixture of polymyxins A, B, C, and D produced byBacillus polymyxa. It was later separated into the major component, B1, and the minor component, B2. Polymyxin B is a basic polypeptide and shows strong activity against gram-negative bacteria, but its activity against gram-positive bacteria, Mycobacterium, and fungi is weak. Because of its toxicity, it is used carefully by intramuscular injection for resistant Pseudomonas aeruginosa infections, e.g., sepsis. Polymyxin B is used orally to sterilize the gut in leukemic patients, intraspinally for meningitis, or topically.
Active against Gram-negative
bacteria, Polymyxin B is a mixture of Polymyxin B1
and B2. Sensitization occurs by topical, ophthalmic,
and otic preparations. Cosensitization is frequent
with other topical antibiotics like neomycin or
bacitracin.
