Metabolism of Drugs by Intestinal Bacteria

Food and drugs orally administered come inevitably in contact with intestinal bacterial flora in gut. The components in food and drugs are digested in the gut and absorbed from the alimentary tract via portal vein and then metabolized or detoxicated in the liver. Thereafter a part of metabolites are excreted into intestine via bile duct and meet again intestinal bacteria. Not only exogeneous substances but also endogenous ones once excreted in the bile come in contact with intestinal bacterial flora. Drugs administered intravenously, intramuscularly or intracutaneously also have chance to meet with intestinal bacteria when once excreted in the bile. Therefore, microflora in the gastrointestinal flora play significant roles in the enterohepatic circulation of drugs and food components. Accordingly, studies on the metabolism of drugs with intestinal microflora are important for research and development of medicines. However, such metabolic studies are very seldom, compared with the studies with liver, kidney, lung and other organs, because of huge numbers and species of anaerobic bacteria and for lack of biochemical studies on anaerobes. Intestinal bacterial flora are an environmental large factor in the body and almost equal to liver in weight and function, though their activities are mostly unknown. Recently, isolation, cultivation and identification techniques of intestinal bacteria from humans and experimental animals have been established. Therefore, metabolisms of food components and drugs with intestinal bacteria are able to be undertaken, based on biochemical and molecular biological backgrounds.