Transport of theophylline from blood to the intestinal lumen following i.v. administration to rats.

Abstract

The exsorption of theophylline into the small intestinal lumen after i.v. administraiton of aminophylline was studied by in situ single-pass perfusion technique. As the concentrations of the drug in the serum and the bile juice were decreased, the exsorption rate of the drug into the perfusate decreased obeying the apparent 1st-order kinetics. The half-lives of the drug concentrations in the serum and the bile juice were 2.13 and 2.58 h for pH 6.0 isotonic phosphate buffer, and were 2.71 and 2.32 h for pH 8.0 isotonic phosphate buffer, respectively. The amounts of theophylline excreted in the perfusate and the bile juice were 12.08% and 0.17% of dose for pH 6.0 isotonic phosphate buffer, and were 13.81% and 0.20% of dose for pH 8.0 isotonic phosphate buffer. A considerable amount of theophylline was exsorbed into the intestinal lumen. The mechanism by which oral activated charcoal enhanced clearance of theophylline administered i.v. may be adsorption of the drug transported into the gastrointestinal tract by the charcoal.