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Polymyxins: An overview

Denis Spelman, MBBS, FRACP, FRCPA, MPH
Section Editor
David C Hooper, MD
Deputy Editor
Allyson Bloom, MD


The polymyxins comprise a separate class of antibiotics and include a number of different compounds. However, only polymyxin B and polymyxin E (also known as colistin) are in clinical use [1]. They were isolated from Paenibacillus polymyxa and became available for clinical use in the 1950s [2,3]. Colistin was historically given as an intramuscular injection for the treatment of gram-negative bacterial infections, but fell out of favor after aminoglycosides became available because of its significant side effects, particularly nephrotoxicity.

More recently, intravenous polymyxin B and colistin have been used more frequently in the treatment of otherwise panresistant nosocomial infections, especially those due to Pseudomonas and Acinetobacter spp [4-8]. They are also used in aerosolized form for patients with cystic fibrosis. (See "Cystic fibrosis: Antibiotic therapy for chronic pulmonary infection".)

Polymyxin B and colistin have almost identical chemical structures and comparable mechanisms of action, resistance patterns, and spectra of activity. However, they have very different pharmacokinetics and pharmacodynamics [9]. These will all be reviewed here along with their adverse effects. The clinical settings in which the polymyxins may be used are discussed separately in the appropriate topic reviews.


Polymyxins are bactericidal drugs that bind to lipopolysaccharides (LPS) and phospholipids in the outer cell membrane of gram-negative bacteria. They competitively displace divalent cations from the phosphate groups of membrane lipids, which leads to disruption of the outer cell membrane, leakage of intracellular contents, and bacterial death [3,10,11].

In addition to their bactericidal effect, the polymyxins can bind and neutralize LPS and may reduce the pathophysiologic effects of endotoxin in the circulation [12,13].

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Literature review current through: Nov 2017. | This topic last updated: Nov 01, 2017.
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