Polymyxins are cationic detergent antibiotics, with a general structure of a cyclic peptide with a long hydrophobic tail. They disrupt the structure of the bacterial cell membrane by interacting with its phospholipids. Polymyxins have a bactericidal effect on Gram-negative bacilli, especially on pseudomonas and coliform organisms. Polymyxin antibiotics are highly neurotoxic and nephrotoxic, and very poorly absorbed from the gastrointestinal tract.

Well known examples:

• Colistin
• Polymyxin B
• Surfactin