INVITRO EVALUATION OF ANTACIDS AT GASTRIC AND DUODENAL SITES

A valid in vitro evaluation of antacid capacity should consider: 1) the intragastric pH-range ; 2) the antacid mechanism ; 3) the dependence of antacid activity from intraluminal flux variations; 4) the interaction between proteins and antacids. Pharmacologically, a static method allows 1) to quantify H+ binding sites at different pH-end points of the titration : pH 3.0, 2.0 and 1.0 and 2) to characterize the antacid mechanism, neutralizing activity and/or buffering capacity. In dynamic conditions, using the <<artificial stomach-duodenum>> model the antacid-induced resistance to acidification was measured, the antacid mechanisms were characterized in regard to intraluminal gastroduodenal flux variations and the incidence of antacid activity on duodenal pH was evaluated. These procedures were applied to antacid evaluation of proteins, as natural antacids, and of drugs containing aluminium salts alone or combined with magnesium salts. Pharmacologically, antacid drugs exhibited a greater amount of H+ binding sites when titration end-point was pH 1.0 than pH 3.0 corresponding to the development of neutralizing activity and/or buffering capacity. In dynamic conditions, the drugs, like proteins, induced a potent resistance to acidification related to gastric emptying fluxes. Antacid effect was supported by neutralizing activity and/or by buffering capacity. It was prolonged by removal of H+ ions since lagtimes for recovering initial pH were longer than antacid total emptying, the dilution of intragastric content by H+ impoverished secretory flux contributing thus to prevent gastric acidification. At duodenal site, proteins and aluminium-containing antacids induced the same duodenal pH as controls, without antacids, while magnesium-containing antacids increased it.