Route of administration

thumb|Oral administration of a liquid.

In pharmacology and toxicology, a route of administration (ROA) is the way by which a drug, fluid, poison, or other substance is introduced into the body.

Routes of administration are generally classified by the location at which the substance is applied. Common examples include oral and intravenous administration. Routes can also be classified based on where the target of action is. Action may be topical (local), enteral (system-wide effect, but delivered through the gastrointestinal tract), or parenteral (systemic action, but is delivered by routes other than the GI tract). Route of administration and dosage form are aspects of drug delivery.

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 is usually rather a matter of pharmacodynamics (concerning, for example, 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,

By application location

Enteral/gastrointestinal route

Through the gastrointestinal tract is sometimes termed enteral or enteric administration (literally meaning 'through the intestines'). Enteral/enteric administration usually includes oral 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 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. The Murphy drip is an example of rectal infusion.

Parenteral route

thumb|Needle insertion angles for 4 types of parenteral administration of medication: intramuscular, subcutaneous, intravenous, and intradermal injection.

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.

thumb|A transdermal patch which delivers medication is applied to the skin. The patch is labelled with the time and date of administration as well as the administrator's initials.

thumb|A medical professional applies nose drops.

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.

thumb|Topical ocular administration

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, and oral spray or vaginal suppository for nitroglycerine.

Topical route

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

Choice of routes

The choice of routes of drug administration is governed by various factors:

Physical and chemical properties of the drug. The physical properties are solid, liquid and gas. The chemical properties are solubility, stability, pH, irritancy, etc.
Site of desired action: the action may be localised and approachable or generalised and not approachable.
Rate of extent of absorption of the drug from different routes.
Effect of digestive juices and the first pass metabolism of drugs.
Condition of the patient.

In acute situations, in emergency medicine and intensive care medicine, drugs are most often given intravenously. This is the most reliable route, as in acutely ill patients the absorption of substances from the tissues and from the digestive tract can often be unpredictable due to altered blood flow or bowel motility.

Convenience

Enteral routes are generally the most convenient for the patient, as no punctures or sterile procedures are necessary. Enteral medications are therefore often preferred in the treatment of chronic disease. However, some drugs can not be used enterally because their absorption in the digestive tract is low or unpredictable. Transdermal administration is a comfortable alternative; there are, however, only a few drug preparations that are suitable for transdermal administration.

Desired target effect

Identical drugs can produce different results depending on the route of administration. For example, some drugs are not significantly absorbed into the bloodstream from the gastrointestinal tract and their action after enteral administration is therefore different from that after parenteral administration. This can be illustrated by the action of naloxone (Narcan), an antagonist of opiates such as morphine. Naloxone counteracts opiate action in the central nervous system when given intravenously and is therefore used in the treatment of opiate overdose. The same drug, when swallowed, acts exclusively on the bowels; it is here used to treat constipation under opiate pain therapy and does not affect the pain-reducing effect of the opiate.

Oral

The oral route is generally the most convenient and costs the least. For drugs that come in delayed release or time-release formulations, breaking the tablets or capsules can lead to more rapid delivery of the drug than intended. ionic liquids, lipid-based nanocarriers, enzyme inhibitors and microneedles have shown potential.

Oral administration is often denoted as "PO" from "per os", the Latin word for "by mouth".

The bioavailability of oral administration is affected by the amount of drug that is absorbed across the intestinal epithelium and first-pass metabolism.

Oral mucosal

The oral mucosa is the mucous membrane lining the inside of the mouth.

Buccal

Buccally administered medication is achieved by placing the drug between gums and the inner lining of the cheek.

Sublingual

Sublingual administration is fulfilled by placing the drug between the tongue and the lower surface of the mouth. It is often the route of administration of choice when one would like the drug to bypass or alleviate the first pass effect on the drug after oral delivery. This is because drug absorption through the nasal passages does not go through the gut before entering capillaries situated at tissue cells and then systemic circulation and such absorption route allows transport of drugs into the central nervous system via the pathways of olfactory and trigeminal nerve. However, skin irritation may result, and for some forms such as creams or lotions, the dosage is difficult to control.) and intradermal (ID) administration.

Parenteral administration generally acts more rapidly than topical or enteral administration, with onset of action often occurring in 15–30 seconds for IV, 10–20 minutes for IM and 15–30 minutes for SC. They also have essentially 100% bioavailability and can be used for drugs that are poorly absorbed or ineffective when they are given orally. Some medications, such as certain antipsychotics, can be administered as long-acting intramuscular injections. Ongoing IV infusions can be used to deliver continuous medication or fluids.

Disadvantages of injections include potential pain or discomfort for the patient and the requirement of trained staff using aseptic techniques for administration.]]

Inhaled medications can be absorbed quickly and act both locally and systemically. The remainder of 50-70% undeposited aerosolized particles are cleared out of lung as soon as exhalation. This should in no way suggest to clinicians or researchers that inhaled particles are not a greater threat than swallowed particles, it merely signifies that a combination of both methods may occur with some particles, no matter the size of or lipo/hydrophilicity of the different particle surfaces.

References

External links

The 10th US-Japan Symposium on Drug Delivery Systems
FDA Center for Drug Evaluation and Research Data Standards Manual: Route of Administration.
FDA Center for Drug Evaluation and Research Data Standards Manual: Dosage Form.
A.S.P.E.N. American Society for Parenteral and Enteral Nutrition