OBJECTIVE To determine the physical and chemical compatibilities of ciprofloxacin lactate infusion with other commonly used intravenously administered drugs. METHODS Ciprofloxacin lactate injection in a commercially available concentration of 2 mg/mL was mixed with 15 intravenous drugs during simulated Y-site injection. Ciprofloxacin was mixed with usually employed concentrations of other drugs in a 1:1 ratio and examined physically by visual inspection and chemically by HPLC analysis. Adsorption of ciprofloxacin to intravenous administration sets with or without inline filters was also studied. METHODS The study was carried out at ambient temperature (25 degrees C) under fluorescent lighting except for vitamin B complex, which was protected from light. All samples were prepared in a laminar airflow hood. METHODS Physical incompatibility was determined by visual inspection against a black-and-white background, and chemical incompatibility was measured by a stability-indicating HPLC assay for ciprofloxacin. Concentrations determined at time zero (before mixing) were defined as 100 percent. Values estimated for each sample at subsequent time points were calculated as percentages of the initial concentration. Recovery below 90 percent of the initial concentration is defined as significant loss. RESULTS Of the 15 drugs studied, only heparin, furosemide, and teicoplanin were found to be incompatible with ciprofloxacin. Adsorption of ciprofloxacin to administration sets with and without inline filters was minimal. Metronidazole was also found to decrease to 90 percent of its initial concentration immediately upon mixing. CONCLUSIONS Ciprofloxacin ready-to-infuse solution is compatible with most of the drugs studied except heparin, furosemide, teicoplanin, and, perhaps, metronidazole. Because only the stability and potency of ciprofloxacin were studied, further testing is needed to confirm if any chemical deterioration of the other drugs occurred when combined with ciprofloxacin.