Enterohepatic circulation of tetracycline in rats.

The absorption of tetracycline hydrochloride excreted in the bile of rats was evaluated using the insitu intestinal preparation. For comparative purposes, the absorption of the drug from an aqueous solution having the same pH as that of the bile was also determined. After 4 hr, the amounts of tetracycline absorbed from the bile and aqueous solutions were 72.92 and 77.34%, respectively. There was no significant difference in the amount of drug accumulated in the gut tissue. The disappearance of the drug from the intestinal lumen was biexponential, and the kinetic parameters appeared to be similar. It was concluded that tetracycline excreted in the bile is readily absorbed from the rat intestine. Accordingly, biliary excretion does not seem to account for a significant elimination of this antibiotic from the body.