Compatibility and stability of linezolid injection admixed with gentamicin sulfate and tobramycin sulfate

The purpose of this study was to evaluate the physical compatibility and chemical stability of linezolid 200 mg/100mL admixed with gentamicin sulfate 80 mg and tobramycin sulfate 80 mg over 7 days at 4 deg C and 23 deg C. The test samples were prepared by adding the required amount of the aminoglycoside antibiotic to bags of linezolid injection 200mg/100mL. Physical and chemical stability based on drug concentrations initially and after 1, 3, 5, and 7 days of storage at 4 deg C ad 23 deg C were evaluated. The linezolid-aminoglycoside admixtures were clear when viewed in normal fluorescent room light and with a Tyndall beam. Measured turbidity and particulate content were low and exhibited little change. The admixtures remained colorless throughout the study. High-performance liquid chromatography analysis indicated little or no loss of linezolid in any sample stored at either temperature throughtout the study. Gentamicin sulfate and tobramycin sulfate in the linezolid admixtures at 4 deg C remained stable for 7 days, but at 23 deg C gentamicin sulfate was stable for 5 days and tobramycin sulfate was stable for only 1 day before aminoglycoside losses exceeded 10%. Admixtures of linezolid 200mg/100mL with gentamicin sulfate 80 mg and tobramycin sulfate 80 mg were physically compatible and chemically stable for at least 7 days when stored at 4 deg C and for 5 days or 1 day, repectively, at 23 deg C.