Polymyxin B sulfate is a mixture of polymyxins B1 and B2, obtained from Bacillus polymyxa strains. They are basic polypeptides of about eight amino acids and have cationic detergent action on cell membranes. Polymyxin B is used for infections with gram-negative organisms, but may be neurotoxic and nephrotoxic. All gram-positive bacteria, fungi, and the gram-negative cocci, N. gonorrhea and N. menigitidis, are resistant. It is appropriate for treatment of infections of the urinary tract, meninges, and blood stream, caused by susceptible strains of Pseudomonas aeruginosa.