Compatibility and stability of linezolid injection admixed with three quinolone antibiotics

OBJECTIVE: To evaluate the physical compatibility and chemical stability of linezolid 200 mg/100 mL admixed with ciprofloxacin 400 mg, ofloxacin 400 m g, and levofloxacin 500 mg for seven days at 4 and 23 degrees C. METHODS: The test samples were prepared by adding the required amount of th e quinolone antibiotic to bags of linezolid injection. Evaluations for phys ical and chemical stability were performed initially and after one, three, five, and seven days of storage at temperatures of 4 and 23 degrees C. Phys ical stability was assessed using visual observation in normal light and us ing a high-intensity monodirectional light beam. In addition, turbidity and particle content were measured electronically. Chemical stability of the d rugs was evaluated by using stability-indicating HPLC analytical techniques . RESULTS: The linezolid admixtures with levofloxacin and ofloxacin were clea r and pale yellow when viewed in normal fluorescent room light, and slightl y hazy with a green cast when viewed using a Tyndall beam, Measured turbidi ty and particulate content were low and exhibited little change. HPLC analy sis found no loss of the drugs in any sample stored at either temperature t hroughout the study. The linezolid admixtures with ciprofloxacin stored at room temperature (23 degrees C) were clear and nearly colorless in normal r oom light and when viewed using a Tyndall beam. They exhibited little or no change in measured turbidity or particulate content during the study perio d. HPLC analysis found no loss of either drug in seven days. However, the r efrigerated samples were only compatible for 24 hours and developed a gross white precipitate thereafter. CONCLUSIONS: Admixtures of linezolid 200 mg/100 mL with levofloxacin 500 mg and with ofloxacin 400 mg were physically compatible and chemically stable for at least seven days stored at 4 and 23 degrees C. Admixtures of linezo lid with ciprofloxacin 400 mg were compatible and stable for seven days at 23 degrees C, but ciprofloxacin precipitation occurred after 24 hours store d under refrigeration. Linezolid/ciprofloxacin admixtures should not be sto red under refrigeration.