Parenteral

Parenteral administration of a drug uses a means of administration that introduces the dose directly into the body, bypassing digestion, skin absorption, inhalation, etc. Most commonly, some type of injection is used for parenteral therapy, either through a hypodermic syringe or intravenous catheter.

Injection routes include:
 * intradermal: in the surface layer of the skin
 * subcutaneous: below the surface of the skin, but not in muscle or a blood vessel
 * intramuscular: into muscle tissue
 * intravenous: into a vein, often using an indwelling catheter for prolonged therapy
 * intrathecal: through a lumbar puncture into the cerebrospinal fluid

Drugs, including radioisotopes, may be inserted during surgery.