The stability of azacitidine diluted in lactated Ringer's injection was studied. Azacitidine was reconstituted with ice-cold lactated Ringer's injection to concentrations of 2.0 and 0.5 mg/mL and stored in polypropylene syringes at -20 degrees C. On days 1, 3, 7, and 14, the solutions were thawed over 30-45 minutes and the azacitidine concentration was determined by high-performance liquid chromatography immediately after thawing and one, three, and six hours later. Other studies were conducted at 37, 20, and 0-4 degrees C to determine decomposition rate constants for azacitidine at both concentrations. Hydrolysis of azacitidine resulted in a biphasic decline when the log of the percentage of drug remaining was plotted against time. No substantial decomposition occurred during storage at -20 degrees C. In thawed samples, azacitidine concentrations decreased to 90% of the initial concentrations within three hours after reaching room temperature; similar decreases in concentration were seen in nonfrozen samples stored at room temperature. The results of these studies indicate that azacitidine solutions in lactated Ringer's injection can be stored in polypropylene syringes at -20 degrees C for two weeks without decomposition. The thawed solutions should be used within three hours.