The use of radiotelemetry techniques for the in vivo assessment of antacids.

The use of the pH radio pill for the assessment of antacid effect has been evaluated. The correlation between the pH pill and a conventional pH electrode system was high (r2 = 0.997). The records of in vivo pH against time allow unique measurements of antacid efficacy (defined as the integrated area under the pH against time curve) and duration of action to be obtained. Using a free pill, antacid assessments were performed in 13 subjects in the left lateral position. The effects of repeated antacid administrations were studied in five subjects using a pH pill which was prevented from leaving the stomach by tethering it to the teeth. These longer studies were performed in the sitting position. The efficacy (p less than 0.02) and duration of action (p less than 0.02) of sodium citrate 0.3 M were less in those subjects in whom the pill was tethered. The differences between the results of the studies using either a free or a tethered pill can be attributed to posture. The overall duration of action of sodium citrate 15 ml was short, the mean (SEM) value being 42.4 (4.5) minutes in the left lateral position and 21.2 (4.0) minutes in the upright position.