Promixin is a brand name for the antibiotic colistimethate sodium, which is used primarily in the treatment of serious infections caused by certain types of bacteria. It is particularly effective against Gram-negative bacteria, including Pseudomonas aeruginosa, which can cause severe infections in the lungs, especially in patients with cystic fibrosis. Promixin works by disrupting the outer membrane of the bacteria, leading to bacterial death. It is often administered via inhalation for lung infections or by injection for infections in other parts of the body. Due to its potency and the risk of nephrotoxicity and neurotoxicity, its use is generally reserved for infections that are resistant to safer antibiotics.