When a substance, such as a drug or solution, is introduced into the body through a route other than the gastrointestinal (GI) tract. (The GI tract extends from the mouth to the anus.) For example, a parenteral drug may be given through the veins (intravenous), into the muscles (intramuscular), or through the skin (subcutaneous). Parenteral nutrition refers to feeding a person intravenously.