Polymyxin B

Polymyxin B (also referred to as PMB) are antibiotics primarily used for resistant gram negative infections. Polymyxins bind to the cell membrane and alters its structure making it more permeable. The resulting water uptake leads to cell death. They are cationic, basic proteins that act like detergents. Side effects include neurotoxicity and acute renal tubular necrosis.

1. Family of polypeptides with attached fatty acid; cationic detergent at physiological pH, both hydrophilic and hydrophobic properties
2. Bactericidal for gram-negative; little to no effect on gram-positive since cell wall is too thick to permit access to membrane

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Mechanism of action

1. Alters cytoplasmic membrane permeability by binding to a negatively charged site in the lipopolysaccharide layer which has an electrostatic attraction for the positively charged amino groups in the cyclic peptide portion
2. Fatty acid portion dissolves in hydrophobic region of membrane and disrupts membrane integrity
3. Leakage of cellular molecules, inhibition of cellular respiration
4. Binds and inactivates endotoxin
5. Relative absence of selective toxicity: nonspecific for cell membranes of any type, highly toxic