Use of the unanesthetized rhesus monkey as a model for studying the gastrointestinal absorption of drugs

A model has been developed to study the gastrointestinal absorption of drugs and dosage forms in the unanesthetized rhesus monkey. Chronic vascular catheters were implanted in the iliac vein and the artery to enable the investigator to withdraw blood samples without disturbing the monkey. The vascular catheters also allow intravenous studies to be carried out so that the kinetic parameters of any drug can be determined. Plastic cannulae were implanted surgically in the stomach and in the duodenum very close to the pylorus. These cannulae provide a means of instilling a drug solution or a dosage form directly into the stomach or the duodenum. A technique was developed using Foley catheters to block the pylorus so that a drug solution or drug particles can be maintained in the stomach. With this setup, absorption of a drug specifically from the stomach can be studied. Sample data for salicylic acid absorption from the stomach and the intestine and for carbamazepine absorption following gastric administration of a solution or a broken tablet are presented.