Table 1.

Gastric incubation endpoints after administration of calcium/magnesium carbonate-based antacid (maximum recommended single dose) or placebo

pH profile	Pepsin activity
pH measured every 15 s within the first 5 min; thereafter, every 5 min until the end of the 2-h incubation	1) Cumulative activity: indirect measurement of digested amount of reference protein (BSA) after 0, 2.5, 5, 10, 15, 30, 45, 60, 90, 120 mina
Time to reach pH 3.0, 3.5, 4.0, 4.5 Maximum pH and duration of highest pH value (-0.1 pH unit)	2) Instantaneous activity: mathematical model, where pepsin activity was measured every 0.25 pH units from pH 1–7, using the same measurement of digested BSA as in 1)b

BSA, bovine serum albumin; TCA, trichloroacetic acid

^aUpon precipitating the intact fraction of the reference protein BSA in the samples collected from the incubations using TCA, the digested protein fraction in the resulting supernatant was quantified via an absorbance measurement at 280 nm. This method required a pre-test to determine whether the antacid also resulted in absorbance at 280 nm and thus should be considered. Results of the pre-test indicated that the antacid did not interfere with the detection method at 280 nm; therefore, inclusion of additional blank incubations without BSA but with addition of the antacid was not required in the final experimental setup. ^bUpon exposing BSA during 15 min to standardized pepsin levels, an absorbance measurement at 280 nm was performed after precipitating intact proteins in the sample via TCA. Thus, the digested protein fraction could be determined at each pH, allowing construction of a mathematical model of the relationship between pH and pepsin activity (as measured via the protein digestion method). Construction of the mathematical model led to a regression curve with strong correlation (R2 > 0.98), allowing accurate calculation of the instantaneous pepsin activity