Gastrointestinal Ph And Transit Times

Gastrointestinal (GI) pH and transit times are useful for understanding the oral absorption of drugs (see Tables 3.1 and 3.2). As many drugs exhibit pH-dependent solubility, an understanding of the pH of the various sections of the GI tract is important. In addition, factors such as GI transit time are important for understanding the residence time of molecules in the gut and also for calculation of parameters such as MAD.

Table 3.1. Gastrointestinal pH of rat, dog, and human

Species

pH (Fasted animals)

Stomach

Small intestine

Colon

Rat

1.93-4.15

5.89-7.10

6.23-6.70

Dog

1.80-3.00

6.20-7.3

6.45-6.75

Human

1.1-1.7

6.00-7.5

5.00-6.80

Data from GastroPlus Software (Simulations Plus, Inc., Lancaster, CA), Lui et al. (1986), and Chen et al. (2006)

Data from GastroPlus Software (Simulations Plus, Inc., Lancaster, CA), Lui et al. (1986), and Chen et al. (2006)

Table 3.2. Gastrointestinal transit times of rat, dog, and human

Transit time (min)

Entire gastrointestinal

Species

Stomach

Small intestine

tract

Rat

15

88-109

451-844

Dog

15-96

109-110

770-844

Human

15-78

198-238

1,293-2,350

Data from Davies and Morris (1993) and GastroPlus Software (Simulations Plus, Inc., Lancaster, CA)

Data from Davies and Morris (1993) and GastroPlus Software (Simulations Plus, Inc., Lancaster, CA)

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