Evaluation of gastrointestinal pH and gastric residence time via the Heidelberg radiotelemetry capsule: Pharmaceutical application

The Heidelberg Radiotelemetry Capsule (7 mm diameter x 20 mm length) represents a noninvasive device to monitor gastrointestinal (GI) pH and to evaluate gastric residence time (GRT) in both animals and humans. Due to its large size and indigestible nature, gastric emptying of the Heidelberg capsule occurs during the 5–15 min of Phase III migrating motor complex (MMC), which is responsible for emptying of indigestible debris leftover from a meal, the so-called housekeeper wave of the GI tract. Following initial in vitro accuracy and in vivo reproducibility studies, the Heidelberg capsule was used in young beagle dogs and normal healthy subjects. In the fasting state, gastric pH was comparable in dogs and humans (1.5 ± 0.04 vs. 1.1 ± 0.15, mean ± SEM), where postprandially a more acidic pH was reported in beagle dogs (2.1 ± 0.04 vs. 3.6 ± 0.4). Both duodenal and fasting intestinal pHs were consistently higher in dogs than humans. Although fasting GRT of the Heidelberg capsule was similar between the two species (1.2 ± 0.33 vs. 1.2 ± 0.45 h), high intersubject variability in the GRT estimation was observed in both dogs and humans. The Heidelberg radiotelemetry technique was utilized in several clinical studies to evaluate the influence of physical and physiological parameters which alter the normal GI motility (i.e., food with varying composition and energy density, posture, gender, age, and gastric alkalinization). The results of pH and GRT measurements via the Heidelberg capsule were found to be sensitive and responsive toward factors which alter the GI motility, and therefore, the Heidelberg capsule may be used in the clinical studies as a model for a large, nondisintegrating solid dosage form (i.e., enteric-coated formulations). Subsequently, the Heidelberg capsule was administered together with the enteric-coated aspirin (which is known for high inter- and intra-subject absorption variability) and with a more challenging enteric-coated formulation, diclofenac sodium. The results demonstrated that by reasonable estimation of the GRT, the Heidelberg capsule is capable of explaining and minimizing the traditional absorption variabilities observed with these formulations. In summary, the Heidelberg radiotelemetry device can be used as a noninvasive means of GI pH and transit time. This accurate and reproducible telemetry system mimics the GI transit of a large indigestible solid dosage form and may be used in both animal research and human oral bioavailability/bioequivalency studies. © 1996 Wiley-Liss, Inc.