Polymyxin

Polymyxins are antibiotics, with a general structure consisting of a cyclic peptide with a hydrophobic tail. They disrupt the structure of the bacterial cell membrane by interacting with its phospholipids. They are produced by nonribosomal peptide synthetase systems in Gram-positive bacteria such as Paenibacillus polymyxa and are selectively toxic for Gram-negative bacteria due to their specificity for the lipopolysaccharide molecule that exists within many Gram-negative outer membranes.

Polymyxins B and E (also known as colistin) are used in the treatment of Gram-negative bacterial infections. The global problem of advancing antimicrobial resistance has led to a renewed interest in their use recently.

Polymyxin M is also known as "mattacin".

Polymyxin antibiotics are relatively neurotoxic and nephrotoxic, so are usually used only as a last resort if modern antibiotics are ineffective or are contraindicated. Typical uses are for infections caused by strains of multiple drug-resistant Pseudomonas aeruginosa or carbapenemase-producing Enterobacteriaceae.

Polymyxins B are not absorbed from the gastrointestinal tract, so another route of administration must be chosen, e.g., parenteral (often intravenously) or by inhalation. They are also used externally as a cream or drops to treat otitis externa (swimmers ear). and as a component of triple antibiotic ointment to treat and prevent skin infections.

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