Estimation of gastric pH in cynomolgus monkeys, rats, and dogs using [13C]-calcium carbonate breath test

BackgroundThe determination of gastric pH is important for the confirmation of efficacy of anti-secretory drugs. However, current methods for measurement of gastric pH provide significant stress to animals and humans.AimThe objective of this study is to establish an easy and reliable gastric pH measurement method by determining 13CO2 concentration in expired air of monkeys, dogs, and rats after oral administration of Ca13CO3.MethodsA correlation of 13CO2 concentration determined by a Ca13CO3 breath test with gastric pH just before Ca13CO3 administration was analyzed in the 3 animal species. The equations and contribution ratios of regression line were calculated from logarithmic 13CO2 concentrations at 15 min after administration of Ca13CO3 using the linear regression analysis.ResultsThe 13CO2 concentration in the Ca13CO3 breath test was well correlated with the gastric pH just before Ca13CO3 administration in the 3 animal species (r = −0.977 to −0.952). The equations of regression line between the 13CO2 concentration and the gastric pH in each animal species showed good contribution ratios (R2 ≥ 0.89).ConclusionsThe Ca13CO3 breath test is an informative tool to estimate gastric pH in animals and will be applicable as a new noninvasive tool for patients with GERD/PPI-resistant symptoms.