Pharmacokinetics of diltiazem absorption in the rat gastrointestinal tract

The absorption of diltiazem (CAS 42399-41-7) from the stomach, small intestine, and colon of the rat has been studied, using an in situ cannulation procedure. Diltiazem solutions (1 mg/ml) were prepared in isotonic buffers at pH 3.5 (stomach), 6.2 (small intestine), or 7.5 (colon). 10 ml of drug solution was used in the small intestine, 4 ml was used in the stomach and colon. Aliquot (100 microliters) of the solution was withdrawn at 5-min intervals for a period of 30 min, and assayed by HPLC. A semilog plot of percent remaining vs. time showed that absorption followed apparent first order kinetics with absorption rate constant, ka, equal 0.07 min-1, 0.02 min-1, and 0.01 min-1, in the small intestine, colon, and stomach, respectively.