The stability and compatibility of ciprofloxacin with selected drugs in intravenous admixtures were studied. Ciprofloxacin 2 mg/mL in 5% dextrose was combined with each of 22 other drugs at concentrations commonly used in clinical practice. Each combination was maintained at room temperature (approximately 22 degrees C) in constant fluorescent light. Immediately after preparation and at 6 and 24 hours, each admixture was examined visually in normal fluorescent room light and the pH value was determined. For samples lacking visible precipitates or having pH changes of not more than 1 unit, ciprofloxacin concentration was assayed by using high-performance liquid chromatography. When combined with ciprofloxacin, 14 of the study drugs did not alter the concentration of ciprofloxacin, including amikacin sulfate, atracurium besylate, aztreonam, cimetidine hydrochloride, dobutamine hydrochloride, fluconazole, gentamicin sulfate, metronidazole (intravenous, ready to use), midazolam hydrochloride, norepinephrine bitartrate, pancuronium bromide, potassium chloride, tobramycin sulfate, and vecuronium bromide. There were five drugs that were determined to be incompatible with ciprofloxacin because of precipitate formation (amphotericin B, ampicillin sodium/sulbactam sodium, cefuroxime sodium, piperacillin sodium, and sodium bicarbonate). Incompatibility with ciprofloxacin based on pH changes of more than 1 unit was found with four drugs: ampicillin sodium/sulbactam sodium, ceftazidime, metronidazole hydrochloride (powder only), and ticarcillin disodium/clavulanate potassium. Intravenous ciprofloxacin 2 mg/mL admixed in 5% dextrose was stable and compatible with 14 of the 22 test drugs for up to 24 hours at room temperature. The other eight drugs should not be combined with ciprofloxacin.