A POLYMYXIN antibiotic active against many gram-negative organisms, including Pseudomonas aeruginosa. It is not absorbed by mouth and therefore needs to be given by injection to obtain a systemic effect; this is rarely indicated, however, as it has serious adverse effects. Colistin is used by mouth in bowel-sterilisation regimens before surgery in patients. It is given by inhalation of a nebulised solution as an adjunct to some standard antibiotic therapy, and is included in some topical preparations, chiefly for skin, eye and ear infections.