Colistin (polymyxin E) is a polymyxin antibiotic produced by certain strains of Bacillus polymyxa var. colistinus. Colistin is a mixture of cyclic polypeptides colistin A and B. Colistin is effective against Gram-negative bacilli, except Proteus.

Administration

Colistin is used as a sulphate or as sulphomethylated form, colistimethate. Colistin sulphate tablets are used to treat intestinal infections, or to suppress colon flora. Colistin sulphate is also used as topical creams, powders, and otic solutions. Colistimethate is used for parenteral administration, and also as an aerosol to treat pulmonary infections.

Mode of action

Colistin is polycationic and has both hydrophobic and lipophilic moieties. These interact with the bacterial cytoplasmic membrane, changing its permeability. This effect is bactericidal.

Pharmacokinetics

The absorption of colistin from the gastrointestinal tract is very poor. The main elimination route of colistin is through renal excretion.