Used primarily as an antibiotic in veterinary medicine and sometimes in human medicine for treating infections caused by multidrug-resistant Gram-negative bacteria. It is especially effective against pathogens like Pseudomonas aeruginosa, Acinetobacter baumannii, and Klebsiella pneumoniae. Due to rising resistance to other antibiotics, colistin sulfate has regained importance as a last-resort treatment in severe hospital-acquired infections. It works by disrupting the bacterial cell membrane, leading to cell death. Commonly administered orally in animals since it has poor systemic absorption, limiting its use in human intravenous formulations to critical cases due to potential nephrotoxicity and neurotoxicity. Also used in selective media in microbiology labs to suppress Gram-negative bacteria during isolation of specific pathogens.