<P> In general medicine, enteral administration (Greek enteros, "intestine") is food or drug administration via the human gastrointestinal tract . This contrasts with parenteral nutrition or drug administration (Greek para, "besides" + enteros), which occurs from routes outside the GI tract, such as intravenous routes . Enteral administration involves the esophagus, stomach, and small and large intestines (i.e., the gastrointestinal tract). Methods of administration include oral, sublingual (dissolving the drug under the tongue), and rectal . Parenteral administration is via a peripheral or central vein . In pharmacology, the route of drug administration is important because it affects drug metabolism, drug clearance, and thus dosage . </P> <P> Enteral administration may be divided into three different categories, depending on the entrance point into the GI tract: oral (by mouth), gastric (through the stomach), and rectal (from the rectum). (Gastric introduction involves the use of a tube through the nasal passage (NG tube) or a tube in the belly leading directly to the stomach (PEG tube). Rectal administration usually involves rectal suppositories .) </P>

Drugs that are subjected to the first pass affect enter the body by which route