In pharmacology
Pharmacology is the branch of medicine and biology concerned with the study of drug action. More specifically, it is the study of the interactions that occur between a living organism and chemicals that affect normal or abnormal biochemical function...

, Enteral (Greek, enteros : Intestine) is a term used to describe routes of drug administration that involve absorption of the drug through the gastrointestinal tract
Gastrointestinal tract
The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....

. The term may also be used to describe something as residing in the gastrointestinal tract. This is contrasted with the term parenteral
Parenteral is a route of administration that involves piercing the skin or mucous membrane. Parenteral nutrition refers to providing nutrition via the veins.-Etymology:...

 (greek para: Besides + enteros: Intestine), meaning outside the intestines, or more specifically in pharmacology: Methods of introducing drugs
Destroy Rebuild Until God Shows are an American post-hardcore band formed in 2010. They released their debut self-titled album on February 22, 2011.- Formation :...

 or substances into the body other than through the gastrointestinal tract, via, for example, intravenous injection.

Forms of enteral administration

Enteral administration may be divided into two different categories, oral and rectal.
Oral administration
Oral administration
Oral administration is a route of administration where a substance is taken through the mouth.-Terminology:Per os is an adverbial phrase meaning literally from Latin "by mouth" or "by way of the mouth." The expression is used in medicine to describe a treatment that is taken orally. The...

Rectal administration
Solids Liquids -
Pill or The Pill may refer to:* Pill , referring to anything small and round for a specific dose of medicine. The term is used colloquially in several ways:** A tablet or capsule which replaced dosing via pill...

In chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.- Types of solutions :...

A tablet is a pharmaceutical dosage form. It comprises a mixture of active substances and excipients, usually in powder form, pressed or compacted from a powder into a solid dose...

A softgel is an oral dosage form for medicine similar to capsules. They consist of a gelatin based shell surrounding a liquid fill. Softgel shells are a combination of gelatin, water, opacifier and a plasticiser such as glycerin and/or sorbitol....

A suppository is a drug delivery system that is inserted into the rectum , vagina or urethra , where it dissolves.They are used to deliver both systemically-acting and locally-acting medications....

Time release technology Suspension
Suspension may refer to:In science and engineering:*Suspension , in mathematics*Suspension , in mathematics*Suspension , mixture of two chemicals with the property that one does not rapidly settle out...

An enema is the procedure of introducing liquids into the rectum and colon via the anus. The increasing volume of the liquid causes rapid expansion of the lower intestinal tract, often resulting in very uncomfortable bloating, cramping, powerful peristalsis, a feeling of extreme urgency and...

Osmotic controlled release capsule
OROS, , is a controlled release oral drug delivery system in the form of a tablet. The tablet has a rigid water-permeable jacket with one or more laser drilled small holes...

An emulsion is a mixture of two or more liquids that are normally immiscible . Emulsions are part of a more general class of two-phase systems of matter called colloids. Although the terms colloid and emulsion are sometimes used interchangeably, emulsion is used when both the dispersed and the...

Murphy drip
Murphy drip
A Murphy drip is a rectal infusion apparatus to administer the medical procedure of proctoclysis, also known as rectoclysis. During the procedure, an end of the Murphy drip is inserted into the rectum and large quantities of liquid are infused into the rectum drop-by-drop...

In cooking, a syrup is a thick, viscous liquid consisting primarily of a solution of sugar in water, containing a large amount of dissolved sugars but showing little tendency to deposit crystals...

Nutrient enema
Nutrient enema
A nutrient enema, also known as feeding per rectum, rectal alimentation, or rectal feeding, is an enema administered with the intent of providing nutrition when normal eating is not possible...

An elixir is a clear, sweet-flavored liquid used for medicinal purposes, to be taken orally and intended to cure one's ills. When used as a pharmaceutical preparation, an elixir contains at least one active ingredient designed to be taken orally....

A tincture is an alcoholic extract or solution of a non-volatile substance . To qualify as a tincture, the alcoholic extract is to have an ethanol percentage of at least 40-60%...


Drug absorption from the intestine

The mechanism for drug absorption from the intestine is for most drugs passive transfer, a few exceptions include levodopa
L-DOPA is a chemical that is made and used as part of the normal biology of some animals and plants. Some animals including humans make it via biosynthesis from the amino acid L-tyrosine. L-DOPA is the precursor to the neurotransmitters dopamine, norepinephrine , and epinephrine collectively...

 and fluorouracil
Fluorouracil is a drug that is a pyrimidine analog which is used in the treatment of cancer. It is a suicide inhibitor and works through irreversible inhibition of thymidylate synthase. It belongs to the family of drugs called antimetabolites...

, which are both absorbed through carrier-mediated transport. For passive transfer to occur, the drug has to diffuse through the lipid cell membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...

 of the epithelial cells lining the inside of the intestines. The rate at which this happens is largely determined by two factors: Ionization
Ionization is the process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or other ions. This is often confused with dissociation. A substance may dissociate without necessarily producing ions. As an example, the molecules of table sugar...

 and lipid solubility .

Factors influencing gastrointestinal absorption:
  • Gastrointestinal motility.
  • Splanchnic
    Splanchnic, from a Greek word spēn, meaning organ, usually used to describe visceral organs.More specifically, it can also refer to:* An adjective describing the intestines* Splanchnic nerves* Splanchnic mesoderm...

     blood flow.
  • Particle
    A particle is, generally, a small localized object to which can be ascribed physical properties. It may also refer to:In chemistry:* Colloidal particle, part of a one-phase system of two or more components where the particles aren't individually visible.In physics:* Subatomic particle, which may be...

     size and formulation.
  • Physicochemical factors.

First pass metabolism

Drugs given by enteral administration may be subjected to significant first pass metabolism, and therefore, the amount of drug entering the systemic circulation following administration may vary significantly for different individuals and drugs.
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