Enterohepatic Recycling

Abstract

Broadly speaking, enterohepatic recycling (or enterohepaticcirculation) involves the circulation of metabolized and non-metabolizedcompounds (including physiologic compounds and xenobiotics) between theintestine and the liver. Some xenobiotics and some endogenous substances (e.g.,bile acids) can be reabsorbed after their elimination into the intestineby the liver, entering an enterohepatic cycle. Enterohepatic circulation can beregarded as the phenomenon of the transport of chemical compounds from theliver to the bile, which eventually drains into intestine and is followed byreabsorption and then back into the liver. The intestinal microbiota plays acentral role in the enterohepatic recycling phenomenon. Enterohepaticcirculation increases the elimination half-life of many drugs (thus prolongingtheir action) and causes multiple peaks in the plasma drug concentration-timeprofile, which are frequently elusive in terms of pharmacokinetic modeling. Insome cases, enterohepatic recycling may have a substantial toxicological impact,as it can retoxify already detoxified xenobiotic molecules and some organs,i.e., the intestine and the liver, may be reiteratively exposed to the drug.