Visual compatibility of colistin injection with other antibiotics during simulated Y-site administration

The compatibility of colistin with other antibiotics at concentrations commonly used in intensive care units was studied.

A vial of colistin was dissolved in sterile water for injection. The reconstituted solution (colistin base 75 mg/mL) was then diluted in 0.9% sodium chloride injection in polyvinyl chloride (PVC) infusion bag to give a total volume of 100 mL (colistin 1.5 mg/mL). Secondary drugs, including cefoperazone-sulbactam, ceftazidime, ertapenem, fosfomycin, imipenem-cilastatin, linezolid, meropenem, piperacillin-tazobactam, and vancomycin, were reconstituted if necessary and then diluted in 0.9% sodium chloride injection in PVC infusion bags to give final study concentrations of one-hundredth of their initial concentrations. The admixtures were collected in beakers at the end of the i.v. line and stored at 26 °C under constant fluorescent light throughout the study. Compatibility was assessed visually during delivery of each drug pair at time 0 and at 1 hour after starting the infusion. Compatibility was defined as the absence of visually detected particulate formation, haze, precipitation, color change, or gas evolution. Each combination was tested in triplicate.

No particulate formation or other evidence of incompatibility was found in any of the studied drug combinations when observed immediately after mixing or at 1 hour. No particulate matter was observed with the unaided eyes, during microscopic evaluation, or against black and white backgrounds.

Colistin 1.5 mg/mL was visually compatible with single concentrations of 9 other antimicrobial products during simulated Y-site injection at 26 °C without light protection for at least 1 hour.