AANA Journal Course: Update for Nurse Anesthetists-Enterohepatic Recirculation: From Death by Mushroom to...

Enterohepatic recirculation (EHRC) is a multistaged process with the following sequence: liver metabolism, bile secretion, gut metabolism, and reabsorption from the gut back to the systemic circulation. Enterohepatic recirculation prolongs drug half-lives and may be associated with the generation of 1 or more secondary plasma peaks. For EHRC to occur, there is substantial dependence on the flora residing in the gastrointestinal (GI) tract. The role of gut microflora is so essential to our overall homeostasis that it is referred to by some authorities as an endocrine organ or "a second brain." Hepatic metabolism plays the dominant role in the fate of drugs and other xenobiotics that we encounter. The liver is rich in a host of chemical manipulators that can hydrolyze, reduce, oxidize, and conjugate xenobiotics. Many drugs, morphine being a good example, are inactivated by glucuronide or sulfate conjugation, with subsequent movement into the bile and eventual emptying into the GI tract. Once in the GI tract, enzymes produced by gut flora can hydrolyze conjugated drugs in the small and large intestine, resulting in the active form reemerging, with reabsorption likely. The clinical relevance of EHRC is discussed with its major implications for efficacy and safety.