Colistin is a generically available antibiotic that has been available for more than 40 years. However its use fell into decline until the last decade when resistance in Gram negative bacilli has necessitated its reintroduction into clinical practice. It is used for multidrug resistant Acinetobacter and Pseudomonas aeruginosa infections and for KPC-producing organisms. It has potential toxicity to the kidneys and nervous system.