Colistimethate sodiumis an antibiotic. it belongs to a group of antibiotics that are called polymyxins.colomycin is given by injection to treat some types of serious infections caused by certain bacteria. colomycin is used when other antibiotics are not suitable.colomycin is given as an inhalation to treat chronic chest infections in patients with cystic fibrosis.the usual daily dose in adults is 9 million units, divided into two or three doses.1 million unit vial: 2ml sterile water / saline2 million unit vial: 4ml sterile water / saline