Normal and Promoted GI Absorption of Water-Soluble Substances III: Absorption of Antibiotics from Stomach and Intestine of the Rat

Absorption of soluble antibiotics was studied in the doubly ligated stomach of the rat, in the ligated small intestine, and in the intact GI tract. When surface-active absorption promoters are administered with the antibiotic in the ligated stomach, promoted absorption occurs but the onset is slow. When the drug–promoter combination is put in the ligated intestine, blood levels of the drug are elevated to severalfold the normal levels and the rise is extremely rapid. Absorption promoters exert a smaller influence in the intact GI tract. Their effectiveness is confined to the first 30 min., after which approximately normal levels of drug are seen. Emptying of the liquid dose from the stomach at 6–8min. was followed by an immediate rapid rise of blood levels characteristic of the rapid response of the intestine to promoters. Accordingly, the blood level versus time curves obtained when promoters are employed in the intact rat are interpreted to be a result of a rapid but transient promoted absorption in the duodenum–small intestine, with little contribution from promoted gastric absorption.