Classification

Routes of administration are usually classified by application location (or exposition).

The route or course the active substance takes from application location to the location where it has its target effect is usually rather a matter of pharmacokinetics (concerning the processes of uptake, distribution, and elimination of drugs). Exceptions include the transdermal or transmucosal routes, which are still commonly referred to as routes of administration.

The location of the target effect of active substances are usually rather a matter of pharmacodynamics (concerning e.g. the physiological effects of drugs). An exception is topical administration, which generally means that both the application location and the effect thereof is local.

Topical administration is sometimes defined as both a local application location and local pharmacodynamic effect, and sometimes merely as a local application location regardless of location of the effects.

By application locationedit

Enteral/gastrointestinaledit

Administration through the gastrointestinal tract is sometimes termed enteral or enteric administration (literally meaning 'through the intestines'). Enteral/enteric administration usually includes oral (through the mouth) and rectal (into the rectum) administration, in the sense that these are taken up by the intestines. However, uptake of drugs administered orally may also occur already in the stomach, and as such gastrointestinal (along the gastrointestinal tract) may be a more fitting term for this route of administration. Furthermore, some application locations often classified as enteral, such as sublingual (under the tongue) and sublabial or buccal (between the cheek and gums/gingiva), are taken up in the proximal part of the gastrointestinal tract without reaching the intestines. Strictly enteral administration (directly into the intestines) can be used for systemic administration, as well as local (sometimes termed topical), such as in a contrast enema, whereby contrast media is infused into the intestines for imaging. However, for the purposes of classification based on location of effects, the term enteral is reserved for substances with systemic effects.

Many drugs as tablets, capsules, or drops are taken orally. Administration methods directly into the stomach include those by gastric feeding tube or gastrostomy. Substances may also be placed into the small intestines, as with a duodenal feeding tube and enteral nutrition. Enteric coated tablets are designed to dissolve in the intestine, not the stomach, because the drug present in the tablet causes irritation in the stomach.

The rectal route is an effective route of administration for many medications, especially those used at the end of life. The walls of the rectum absorb many medications quickly and effectively. Medications delivered to the distal one-third of the rectum at least partially avoid the "first pass effect" through the liver, which allows for greater bio-availability of many medications than that of the oral route. Rectal mucosa is highly vascularized tissue that allows for rapid and effective absorption of medications. A suppository is a solid dosage form that fits for rectal administration. In hospice care, a specialized rectal catheter, designed to provide comfortable and discreet administration of ongoing medications provides a practical way to deliver and retain liquid formulations in the distal rectum, giving health practitioners a way to leverage the established benefits of rectal administration.

Parenteraledit

The parenteral route is any route that is not enteral (par- + enteral).

Parenteral administration can be performed by injection, that is, using a needle (usually a hypodermic needle) and a syringe, or by the insertion of an indwelling catheter.

Locations of application of parenteral administration include:

• Central nervous system:

• Epidural (synonym: peridural) (injection or infusion into the epidural space), e.g. epidural anesthesia.
• Intracerebral (into the cerebrum) administration by direct injection into the brain. Used in experimental research of chemicals and as a treatment for malignancies of the brain. The intracerebral route can also interrupt the blood brain barrier from holding up against subsequent routes.
• Intracerebroventricular (into the cerebral ventricles) administration into the ventricular system of the brain. One use is as a last line of opioid treatment for terminal cancer patients with intractable cancer pain.

• Epicutaneous (application onto the skin). It can be used both for local effect as in allergy testing and typical local anesthesia, as well as systemic effects when the active substance diffuses through skin in a transdermal route.
• Sublingual and buccal medication administration is a way of giving someone medicine orally (by mouth). Sublingual administration is when medication is placed under the tongue to be absorbed by the body. The word "sublingual" means "under the tongue." Buccal administration involves placement of the drug between the gums and the cheek. These medications can come in the form of tablets, films, or sprays. Many drugs are designed for sublingual administration, including cardiovascular drugs, steroids, barbiturates, opioid analgesics with poor gastrointestinal bioavailability, enzymes and, increasingly, vitamins and minerals.
• Extra-amniotic administration, between the endometrium and fetal membranes.
• Nasal administration (through the nose) can be used for topically acting substances, as well as for insufflation of e.g. decongestant nasal sprays to be taken up along the respiratory tract. Such substances are also called inhalational, e.g. inhalational anesthetics.
• Intra-arterial (into an artery), e.g. vasodilator drugs in the treatment of vasospasm and thrombolytic drugs for treatment of embolism.
• Intra-articular, into a joint space. It is generally performed by joint injection. It is mainly used for symptomatic relief in osteoarthritis.
• Intracardiac (into the heart), e.g. adrenaline during cardiopulmonary resuscitation (no longer commonly performed).
• Intracavernous injection, an injection into the base of the penis.
• Intradermal, (into the skin itself) is used for skin testing some allergens, and also for mantoux test for tuberculosis.
• Intralesional (into a skin lesion), is used for local skin lesions, e.g. acne medication.
• Intramuscular (into a muscle), e.g. many vaccines, antibiotics, and long-term psychoactive agents. Recreationally the colloquial term 'muscling' is used.

• Intraocular, into the eye, e.g., some medications for glaucoma or eye neoplasms.
• Intraosseous infusion (into the bone marrow) is, in effect, an indirect intravenous access because the bone marrow drains directly into the venous system. This route is occasionally used for drugs and fluids in emergency medicine and pediatrics when intravenous access is difficult.
• Intraperitoneal, (infusion or injection into the peritoneum) e.g. peritoneal dialysis.
• Intrathecal (into the spinal canal) is most commonly used for spinal anesthesia and chemotherapy.
• Intrauterine.
• Intravaginal administration, in the vagina.
• Intravenous (into a vein), e.g. many drugs, total parenteral nutrition.
• Intravesical infusion is into the urinary bladder.
• Intravitreal, through the eye.
• Subcutaneous (under the skin). This generally takes the form of subcutaneous injection, e.g. with insulin. Skin popping is a slang term that includes subcutaneous injection, and is usually used in association with recreational drugs. In addition to injection, it is also possible to slowly infuse fluids subcutaneously in the form of hypodermoclysis.
• Transdermal (diffusion through the intact skin for systemic rather than topical distribution), e.g. transdermal patches such as fentanyl in pain therapy, nicotine patches for treatment of addiction and nitroglycerine for treatment of angina pectoris.
• Perivascular administration (perivascular medical devices and perivascular drug delivery systems are conceived for local application around a blood vessel during open vascular surgery).
• Transmucosal (diffusion through a mucous membrane), e.g. insufflation (snorting) of cocaine, sublingual, i.e. under the tongue, sublabial, i.e. between the lips and gingiva, nitroglycerine, vaginal suppositories.

Topicaledit

The definition of the topical route of administration sometimes states that both the application location and the pharmacodynamic effect thereof is local.

In other cases, topical is defined as applied to a localized area of the body or to the surface of a body part regardless of the location of the effect. By this definition, topical administration also includes transdermal application, where the substance is administered onto the skin but is absorbed into the body to attain systemic distribution.

If defined strictly as having local effect, the topical route of administration can also include enteral administration of medications that are poorly absorbable by the gastrointestinal tract. One poorly absorbable antibiotic is vancomycin, which is recommended by mouth as a treatment for severe Clostridium difficile colitis.