The stability of nizatidine in extemporaneous oral liquid preparations stored at room and refrigerated temperatures was studied. Preparations containing nizatidine in a final concentration of approximately 2.5 mg/mL were made by mixing the contents of a 300-mg nizatidine capsule with commercial juices (Gatorade, Stokely-Van Camp; Cran-Grape, Ocean Spray; apple juice, Sundor Brands; and V8 vegetable juice, Campbell Soup) and with aluminum hydroxide-magnesium hydroxide suspension (Maalox, Rorer). A control solution was prepared in water. Samples of each preparation were stored at 15-30 degrees C and at 5 degrees C. Initially and after 4, 8, 24, and 48 hours of storage, the samples were visually inspected, tested for pH, and analyzed in triplicate by high-performance liquid chromatography for nizatidine content. No appreciable changes in appearance or pH occurred. The only extemporaneous preparations with greater than 10% loss of nizatidine potency at 48 hours were the Cran-Grape and V8 preparations at room temperature. There was no correlation between pH of the preparations and changes in drug concentration. In the Maalox and V8 preparations, the drug powder did not dissolve uniformly. In all the preparations tested, nizatidine was stable for at least eight hours at refrigerated and room temperatures. In all except the Cran-Grape and V8 preparations, the drug was stable for 48 hours under both storage conditions.