The potential interaction of the H2-receptor antagonist famotidine (CAS 76824-35-6) with calcium carbonate (CAS 471-34-1) and magnesium hydroxide (CAS 1309-42-8) during administration of the famotidine fixed dose combination (FDC) formulation was investigated. A randomized, open-label, two-period, crossover study was carried out on 12 healthy Chinese volunteers. Plasma concentration-time profiles of famotidine were similar with the FDC formulation and common formulation. Confidence interval (90% CI) for maximal concentration (C(max)) and area under the curve (AUC(o-t)) of famoti-dine were 94.8-112.2% and 94.2-112.3%, respectively. These findings suggest that calcium carbonate/magnesium hydroxide antacids have no significant effects on famotidine pharmacokinetics when they are administered together with famotidine as an FDC formulation.