Furthermore, these data sound the alarm for use of caution in interpreting colistin susceptibility test results, as isolates identified as susceptible may in fact resist antibiotic therapy and ...Colistimethate for Injection, USP is a sterile parenteral antibiotic product which, when reconstituted (see Reconstitution), is suitable for intramuscular or intravenous administration. Each vial contains Colistimethate sodium or pentasodium colistinmethanesulfonate (150 mg colistin base activity). In the latter scenario, the use of intraventricular or intrathecal colistin also permits high local concentrations and good clinical results. Overall, the efficacy of intravenous colistin seems to be poor, but its association with a second antimicrobial significantly increases the response rate.Colistin is a 50 year-old antibiotic that is being used increasingly as a 'last-line' therapy to treat infections caused by MDR Gram-negative bacteria, when essentially no other options are available. Despite its age, or because of its age, there has been a dearth of knowledge on its pharmacological and microbiological properties.