Polymyxin is the name given to a group of five compounds designated by the suffixes A to E. polymyxins A C and D damage the renal tubules and are no longer used. Polymyxin B has been available for many years. More recently colomycin has been introduced as new antibiotics. It is a sulphomethy 1 derivate of colistin and colistin has now been shown to be identical with polymyxin E. These antibiotics have a bactericidal effect against many gram-negative organisms and notably against Pseudomonas pyocyanea. There is evidence of an increasing incidence of infection with this organism especially in debilitated patients. Colomycin is less toxic and less painful to administer than polymyxin B and accordingly is the antibiotic of choice for the treatment of infections due to Ps. Pyocyanea. It is given by intramuscular injection in a dosage determined by the weight of the patient, 50,000 units per kg. Every 24 hours divided into two to four intramuscular injections. Colomycin can also be used by mouth for the treatment of bacillary in reserve to deal with pseudomonas infections. Polymyxin is used in conjunction with backtracking for the topical treatment of wounds, pressure sores, etc.
