Method for quantitative measurement of gastric acidity using 13c carbonate salt

A method for measuring an effect of a gastric acid reducer on a mammal, the method comprising the following steps (1) to (4):

• (1) using, as a test sample, expired air of a mammalian subject excreted at any point in time within 30 minutes after oral administration of a predetermined amount of a 13C-labeled carbonate compound, the oral administration being performed after administration of a gastric acid reducer, measuring behavior of 13CO2 excreted in the expired air,
• (2) comparing the behavior of 13CO2 (measured 13CO2 behavior) obtained in step (1) with the behavior of corresponding 13CO2 (reference 13CO2 behavior) measured in a mammal (control mammal) to which a predetermined amount of a 13C-labeled carbonate compound has been orally administered beforehand without administering the gastric acid reducer;
• (3) determining gastric acidity of the mammalian subject based on a difference between the reference 13CO2 behavior and the measured 13CO2 behavior obtained above;
• and
• (4) determining the effect of the gastric acid reducer on the mammalian subject using the gastric acidity of the mammalian subject obtained above as an index.