Polymyxin B: similarities to and differences from colistin (polymyxin E).

Hospital-acquired infections due to multidrug-resistant gram-negative bacteria constitute major health problems, since the medical community is continuously running out of available effective antibiotics and no new agents are in the pipeline. Polymyxins, a group of antibacterials that were discovered during the late 1940s, represent some of the last treatment options for these infections. Only two polymyxins are available commercially, polymyxin E (colistin) and polymyxin B. Although several reviews have been published recently regarding colistin, no review has focused on the similarities and differences between polymyxin B and colistin. These two medications have many similarities with respect to mechanism of action, antimicrobial spectrum, clinical uses and toxicity. However, they also differ in several aspects, including chemical structure, formulation, potency, dosage and pharmacokinetic properties.