Drug absorption I: An in situ rat gut technique yielding realistic absorption rates

A method is reported for studying gastrointestinal drug absorption from isolated gut segments of the anesthetized rat in situ. The experimental technique is simple and utilizes readily available laboratory equipment. The results are closely reproducible and yield absorption rates which are realistic in terms of the known absorption behavior of drugs in humans and intact animals. Disappearance of the drugs from the lumen of the small intestine followed apparent first-order kinetics; and the following half-lives were determined at pH 6: aminopyrine, 32 min.; barbital, 19 min.; haloperidol, 24 min.; prochlorperazine, 23 min.; salicylic acid, 8 min,; and sulfaethidole, 32 min. These absorption rates are much faster than those normally observed in in situ intestinal preparations. Absorption rates from rat stomach in situ, and preliminary data showing a relationship between fasting time and intestinal absorption rates in the rat are also presented.