Colistin is a narrow-spectrum lipopeptide antimicrobial agent used to treat nosocomial infections caused by multidrug-resistant bacteria, especially in critically ill patients and those with cystic fibrosis. Colistin represents a concentration-time-dependent antibiotic with highly variable pharmacokinetics related to the heterogeneity of the target population and the necessity of bioactivation. Colistin is administered as the inactive prodrug colistimethate sodium. Nephrotoxicity and neurotoxicity are the most frequent adverse effects.