Mucosal biotransformation.

About 4 million compounds have been described by chemists, and some 60,000 are presently on the market. The search for new chemicals with better properties and less toxicity continues, and future life quality will depend on our ability to find the safest compounds in each field of application. During development of new drugs and chemicals, studies on biotransformation should be done very early, and with adequate analytical tools, in order to get an early understanding of data on bioavailability, metabolic pattern, and toxicity. Though the liver is generally the organ with the highest drug metabolizing activity, it becomes increasingly evident that some extrahepatic organs, such as intestine, kidney, skin, and lung also participate in drug metabolism. The peculiar property of intestinal metabolism is the fact that it modifies chemicals before they enter the circulation. Therefore, an understanding of intestinal metabolism is important for proper interpretation of all pharmacological and toxicological data during development of a new compound. Mucosal biotransformation has recently been reviewed. The present work gives a schematic survey on the topic, shows new trends, and discusses the consequences for toxicological testing of new chemicals.