<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>
drugs that are subjected to the first pass affect enter the body by which route
the human gastrointestinal tract