ABSTRACT
The everted intestine model has been used successfully to examine the interaction between some drugs and metal-containing antacid constituents, for example tetracyclines, digoxin, warfarin, phenytoin, propranolol, chloroquine, and pyrimethamine. One of the most important and interesting findings from that study was that dicalcium phosphate depressed the gut absorption of tetracycline. Zinc also has been shown to inhibit the absorption of tetracycline from the gut. They suggested that binding of tetracycline to organic macromolecules within the gut is increased by calcium ions and probably also by other di- and trivalent ions; this, they thought, was the main reason for the impaired permeation across the absorbing epithelium. Further studies showed that the calcium sulfate had apparently interacted with the phenytoin to convert about 25% of the anticonvulsant into a form which was insoluble in chloroform and therefore was unlikely to be absorbed from the gut.
