Colistin methanesulfonate sodium salt is primarily used as an antibiotic in the treatment of severe infections caused by multidrug-resistant Gram-negative bacteria. It is particularly effective against pathogens such as Pseudomonas aeruginosa, Acinetobacter baumannii, and Klebsiella pneumoniae, which are often resistant to other antibiotics. This compound is commonly administered intravenously in hospital settings for conditions like pneumonia, bloodstream infections, and urinary tract infections. In veterinary medicine, it is also used to treat bacterial infections in animals. Due to its potential nephrotoxicity and neurotoxicity, its use is typically reserved for cases where other treatments have failed or are not suitable.