Polymyxin B is an antibiotic that belongs to the class of drugs known as polymyxins. It is primarily used to treat infections caused by certain types of bacteria, particularly Gram-negative bacteria, which are often resistant to other antibiotics. Polymyxin B works by disrupting the bacterial cell membrane, leading to cell death. This antibiotic is commonly used in topical formulations for skin infections and in some cases for serious infections when other treatments are ineffective. However, it can have side effects, including kidney toxicity, so its use is generally reserved for specific situations under medical supervision.