Antacid activity of calcium carbonate and hydrotalcite tablets. Comparison between in vitro evaluation using the "artificial stomach-duodenum" model and in vivo pH-metry in healthy volunteers.

Antacid activity of calcium carbonate (CAM, Rennie) and of hydrotalcite (HYD) containing tablets has been assessed in vitro using computer-controlled "artificial stomach-duodenum" model, including or not a piece of hog gastric mucosa in the gastric reservoir, and simulating the constant flux system or the normal gastroduodenal flux regulation. The data obtained under the latter condition were compared to those obtained in vivo by pH-metry in 12 healthy volunteers, in response to one administration of 2 tablets. The theoretical maximal capacity was similar when 1 tablet of CAM or of HYD was added to the gastric contents, including or not a piece of gastric mucosa, close to 95 H+ mmol. The reduction of acid load penetrating into the duodenum and the duodenal pH were of the same magnitude in response to both antacids. When normal gastroduodenal flux regulation was simulated, a dose-response curve, constructed by 1, 2 or 3 tablets, resulted in the same antacid characteristics in response to both antacids. The maximal gastric and the mean duodenal pH values obtained with CAM were, however, higher than with HYD, corresponding to a greater neutralizing activity developed by CAM than by HYD. The comparison between in vivo administration of two tablets of each antacid and the in vitro model simulating normal gastroduodenal flux regulation in response to the addition of two tablets resulted in similar data. The maximal pH values obtained in in vivo assays were slightly lower than in vitro, depending on the ratio of antacid amount to gastric acid content, well established in in vitro conditions and unknown in in vivo situations.(ABSTRACT TRUNCATED AT 250 WORDS)