Compatibility and stability of linezolid injection admixed with three cephalosporin antibiotics.

OBJECTIVE: To evaluate the physical compatibility and chemical stability of linezolid (Zyvox-Pharmacia) 200 mg/100 mL admixed with cefazolin sodium 1 gram, ceftazidime 2 grams, and ceftriaxone sodium 1 gram for 7 days at 4 degrees C and 23 degrees C. DESIGN: Controlled experimental trial. SETTING: Laboratory. INTERVENTIONS: The test samples were prepared by adding the required amount of the cephalosporin antibiotic to bags of linezolid injection 200 mg/100 mL. MAIN OUTCOME MEASURES: Physical stability and chemical stability based on drug concentrations initially and after 1, 3, 5, and 7 days of storage at 4 degrees C and 23 degrees C protected from light. RESULTS: All of the linezolid admixtures with cephalosporins 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 cefazolin sodium-containing samples were colorless throughout the study. The admixtures with ceftazidime and ceftriaxone sodium had a slight yellow tinge initially, and the room temperature samples became a frank yellow color after 5 days. The refrigerated samples did not change color. High-performance liquid chromatography analysis found little or no loss of linezolid in any sample stored at either temperature throughout the study. Cefazolin sodium and ceftazidime in the linezolid admixtures at 4 degrees C remained stable for 7 days, but at 23 degrees C cefazolin sodium was stable for 3 days and ceftazidime for only 24 hours before cephalosporin decomposition exceeded 10%. Ceftriaxone sodium was less stable in the admixtures; 10% loss occurred in 3 days at 4 degrees C and more than 20% loss occurred in 24 hours at 23 degrees C. CONCLUSION: Admixtures of linezolid 200 mg/100 mL with cefazolin sodium 1 gram and ceftazidime 2 grams were physically compatible and chemically stable for at least 7 days stored at 4 degrees C protected from light and for 3 days and 1 day, respectively, at 23 degrees C protected from light. Admixtures of linezolid with ceftriaxone sodium 1 gram exhibited a rapid rate of cephalosporin loss at 23 degrees C, which precludes admixture of the two drugs.