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A route of administration in
pharmacology Pharmacology is a branch of medicine, biology and pharmaceutical sciences concerned with drug or medication action, where a drug may be defined as any artificial, natural, or endogenous (from within the body) molecule which exerts a biochemica ...
and
toxicology Toxicology is a scientific discipline, overlapping with biology, chemistry, pharmacology, and medicine, that involves the study of the adverse effects of chemical substances on living organisms and the practice of diagnosing and treating e ...
is the way by which a
drug A drug is any chemical substance that causes a change in an organism's physiology or psychology when consumed. Drugs are typically distinguished from food and substances that provide nutritional support. Consumption of drugs can be via inhala ...
, fluid, poison, or other substance is taken into the body. Routes of administration are generally classified by the location at which the substance is applied. Common examples include
oral The word oral may refer to: Relating to the mouth * Relating to the mouth, the first portion of the alimentary canal that primarily receives food and liquid ** Oral administration of medicines ** Oral examination (also known as an oral exam or or ...
and intravenous administration. Routes can also be classified based on where the target of action is. Action may be
topical A topical medication is a medication that is applied to a particular place on or in the body. Most often topical medication means application to body surfaces such as the skin or mucous membranes to treat ailments via a large range of classes ...
(local), enteral (system-wide effect, but delivered through the gastrointestinal tract), or
parenteral A route of administration in pharmacology and toxicology is the way by which a drug, fluid, poison, or other substance is taken into the body. Routes of administration are generally classified by the location at which the substance is applied. ...
(systemic action, but 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 Pharmacokinetics (from Ancient Greek ''pharmakon'' "drug" and ''kinetikos'' "moving, putting in motion"; see chemical kinetics), sometimes abbreviated as PK, is a branch of pharmacology dedicated to determining the fate of substances administered ...
(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 Pharmacodynamics (PD) is the study of the biochemical and physiologic effects of drugs (especially pharmaceutical drugs). The effects can include those manifested within animals (including humans), microorganisms, or combinations of organisms ...
(concerning e.g. the physiological effects of drugs). An exception is
topical administration A topical medication is a medication that is applied to a particular place on or in the body. Most often topical medication means application to body surfaces such as the skin or mucous membranes to treat ailments via a large range of classes ...
, which generally means that both the application location and the effect thereof is local.
Topical administration A topical medication is a medication that is applied to a particular place on or in the body. Most often topical medication means application to body surfaces such as the skin or mucous membranes to treat ailments via a large range of classes ...
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.thefreedictionary.com > topical
Citing: The American Heritage Dictionary of the English Language, Fourth Edition, 2000


By application location


Enteral/gastrointestinal

through the gastrointestinal tract is sometimes termed ''enteral or enteric administration'' (literally meaning 'through the intestines'). ''Enteral/enteric administration'' usually includes ''
oral The word oral may refer to: Relating to the mouth * Relating to the mouth, the first portion of the alimentary canal that primarily receives food and liquid ** Oral administration of medicines ** Oral examination (also known as an oral exam or or ...
'' (through the
mouth In animal anatomy, the mouth, also known as the oral cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary canal, bounded on ...
) and '' rectal'' (into the
rectum The rectum is the final straight portion of the large intestine in humans and some other mammals, and the gut in others. The adult human rectum is about long, and begins at the rectosigmoid junction (the end of the sigmoid colon) at the l ...
) 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 Sublingual (abbreviated SL), from the Latin for "under the tongue", refers to the pharmacological route of administration by which substances diffuse into the blood through tissues under the tongue. The sublingual glands receive their primary ...
(under the tongue) and sublabial or buccal (between the cheek and gums/
gingiva The gums or gingiva (plural: ''gingivae'') consist of the mucosal tissue that lies over the mandible and maxilla inside the mouth. Gum health and disease can have an effect on general health. Structure The gums are part of the soft tissue l ...
), 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 A topical medication is a medication that is applied to a particular place on or in the body. Most often topical medication means application to body surfaces such as the skin or mucous membranes to treat ailments via a large range of classes ...
), such as in a contrast enema, whereby contrast media are 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 intestine The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most of the #Absorption, absorption of nutrients from food takes place. It lies between the stomach and large intes ...
s, as with a duodenal feeding tube and
enteral nutrition Enteral administration is food or drug administration via the human gastrointestinal tract. This contrasts with parenteral nutrition or drug administration (Greek ''para'', "besides" + ''enteros''), which occurs from routes outside the GI tract, ...
. 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 End-of-life may refer to: * End-of-life (product), a term used with respect to terminating the sale or support of goods and services * End-of-life care End-of-life care (EoLC) refers to health care provided in the time leading up to a person's dea ...
. 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 In pharmacology, bioavailability is a subcategory of absorption and is the fraction (%) of an administered drug that reaches the systemic circulation. By definition, when a medication is administered intravenously, its bioavailability is 100%. H ...
of many medications than that of the oral route. Rectal
mucosa A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It i ...
is highly
vascularized Angiogenesis is the physiological process through which new blood vessels form from pre-existing vessels, formed in the earlier stage of vasculogenesis. Angiogenesis continues the growth of the vasculature by processes of sprouting and splittin ...
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 Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...
rectum, giving health practitioners a way to leverage the established benefits of rectal administration. The
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 in ...
is an example of rectal infusion.


Parenteral

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 A hypodermic needle (from Greek ὑπο- (''hypo-'' = under), and δέρμα (''derma'' = skin)), one of a category of medical tools which enter the skin, called sharps, is a very thin, hollow tube with one sharp tip. It is commonly used ...
) and a
syringe A syringe is a simple reciprocating pump consisting of a plunger (though in modern syringes, it is actually a piston) that fits tightly within a cylindrical tube called a barrel. The plunger can be linearly pulled and pushed along the inside ...
, or by the insertion of an
indwelling catheter In medicine, a catheter (/ˈkæθətər/) is a thin tube made from medical grade materials serving a broad range of functions. Catheters are medical devices that can be inserted in the body to treat diseases or perform a surgical procedure. Cath ...
. 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 Local anesthesia is any technique to induce the absence of sensation in a specific part of the body, generally for the aim of inducing local analgesia, that is, local insensitivity to pain, although other local senses may be affected as well. It ...
, as well as
systemic Systemic fundamental to a predominant social, economic, or political practice. This refers to: In medicine In medicine, ''systemic'' means affecting the whole body, or at least multiple organ systems. It is in contrast with ''topical'' or ''loc ...
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 Extra-amniotic administration is a route of administration to the space between the fetal membranes and endometrium inside the uterus of a pregnant woman. It can be used to administer drugs affecting uterus motility, such as oxytocin and prostagla ...
, 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 The respiratory tract is the subdivision of the respiratory system involved with the process of respiration in mammals. The respiratory tract is lined with respiratory epithelium as respiratory mucosa. Air is breathed in through the nose to ...
. Such substances are also called ''inhalational'', e.g.
inhalational anesthetics An inhalational anesthetic is a chemical compound possessing general anesthetic properties that can be delivered via inhalation. They are administered through a face mask, laryngeal mask airway or tracheal tube connected to an anesthetic vapori ...
. * Intra-arterial (into an
artery An artery (plural arteries) () is a blood vessel in humans and most animals that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are the pu ...
), 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 Osteoarthritis (OA) is a type of degenerative joint disease that results from breakdown of joint cartilage and underlying bone which affects 1 in 7 adults in the United States. It is believed to be the fourth leading cause of disability in the ...
. * Intracardiac (into the heart), e.g. adrenaline during
cardiopulmonary resuscitation Cardiopulmonary resuscitation (CPR) is an emergency procedure consisting of chest compressions often combined with artificial ventilation in an effort to manually preserve intact brain function until further measures are taken to restore spont ...
(no longer commonly performed). * Intracavernous injection, an injection into the base of the
penis A penis (plural ''penises'' or ''penes'' () is the primary sexual organ that male animals use to inseminate females (or hermaphrodites) during copulation. Such organs occur in many animals, both vertebrate and invertebrate, but males d ...
. *
Intradermal Intradermal injection, often abbreviated ID, is a shallow or superficial injection of a substance into the dermis, which is located between the epidermis and the hypodermis. For certain substances, administration via an ID route can result in a ...
, (into the skin itself) is used for
skin testing Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different de ...
some
allergens An allergen is a type of antigen that produces an abnormally vigorous immune response in which the immune system fights off a perceived threat that would otherwise be harmless to the body. Such reactions are called allergies. In technical ter ...
, and also for mantoux test for
tuberculosis Tuberculosis (TB) is an infectious disease usually caused by '' Mycobacterium tuberculosis'' (MTB) bacteria. Tuberculosis generally affects the lungs, but it can also affect other parts of the body. Most infections show no symptoms, ...
. * Intralesional (into a skin lesion), is used for local skin lesions, e.g. acne medication. *
Intramuscular Intramuscular injection, often abbreviated IM, is the injection of a substance into a muscle. In medicine, it is one of several methods for parenteral administration of medications. Intramuscular injection may be preferred because muscles ha ...
(into a
muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of mus ...
), e.g. many
vaccine A vaccine is a biological preparation that provides active acquired immunity to a particular infectious or malignant disease. The safety and effectiveness of vaccines has been widely studied and verified.
s, antibiotics, and long-term psychoactive agents. Recreationally the colloquial term 'muscling' is used. * Intraocular, into the eye, e.g., some medications for
glaucoma Glaucoma is a group of eye diseases that result in damage to the optic nerve (or retina) and cause vision loss. The most common type is open-angle (wide angle, chronic simple) glaucoma, in which the drainage angle for aqueous humor, fluid withi ...
or eye neoplasms. *
Intraosseous infusion Intraosseous infusion (IO) is the process of injecting medications, fluids, or blood products directly into the marrow of a bone; this provides a non-collapsible entry point into the systemic venous system. The intraosseous infusion technique i ...
(into the
bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...
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 The peritoneum is the serous membrane forming the lining of the abdominal cavity or coelom in amniotes and some invertebrates, such as annelids. It covers most of the intra-abdominal (or coelomic) organs, and is composed of a layer of mes ...
) e.g. peritoneal dialysis. * Intrathecal (into the spinal canal) is most commonly used for spinal
anesthesia Anesthesia is a state of controlled, temporary loss of sensation or awareness that is induced for medical or veterinary purposes. It may include some or all of analgesia (relief from or prevention of pain), paralysis (muscle relaxation), ...
and
chemotherapy Chemotherapy (often abbreviated to chemo and sometimes CTX or CTx) is a type of cancer treatment that uses one or more anti-cancer drugs (chemotherapeutic agents or alkylating agents) as part of a standardized chemotherapy regimen. Chemother ...
. * Intrauterine. * Intravaginal administration, in the
vagina In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucosal tissue called the hymen ...
. * Intravenous (into a
vein Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated ...
), 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 Subcutaneous administration is the insertion of medications beneath the skin either by injection or infusion. A subcutaneous injection is administered as a bolus into the subcutis, the layer of skin directly below the dermis and epidermis, c ...
, e.g. with
insulin Insulin (, from Latin ''insula'', 'island') is a peptide hormone produced by beta cells of the pancreatic islets encoded in humans by the ''INS'' gene. It is considered to be the main anabolic hormone of the body. It regulates the metabolism ...
. 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 Fentanyl, also spelled fentanil, is a very potent synthetic opioid used as a pain medication. Together with other drugs, fentanyl is used for anesthesia. It is also used illicitly as a recreational drug, sometimes mixed with heroin, cocain ...
in pain therapy,
nicotine Nicotine is a naturally produced alkaloid in the nightshade family of plants (most predominantly in tobacco and '' Duboisia hopwoodii'') and is widely used recreationally as a stimulant and anxiolytic. As a pharmaceutical drug, it is use ...
patches for treatment of
addiction Addiction is a neuropsychological disorder characterized by a persistent and intense urge to engage in certain behaviors, one of which is the usage of a drug, despite substantial harm and other negative consequences. Repetitive drug use o ...
and nitroglycerine for treatment of angina pectoris. *
Perivascular administration Mural cells are the vascular smooth muscle cells (vSMCs), and pericytes, of the microcirculation. Both types are in close contact with the endothelial cells lining the capillaries, and are important for vascular development and stability. Mural cel ...
(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 Cocaine (from , from , ultimately from Quechua: ''kúka'') is a central nervous system (CNS) stimulant mainly used recreationally for its euphoric effects. It is primarily obtained from the leaves of two Coca species native to South Am ...
,
sublingual Sublingual (abbreviated SL), from the Latin for "under the tongue", refers to the pharmacological route of administration by which substances diffuse into the blood through tissues under the tongue. The sublingual glands receive their primary ...
, i.e. under the tongue, sublabial, i.e. between the lips and
gingiva The gums or gingiva (plural: ''gingivae'') consist of the mucosal tissue that lies over the mandible and maxilla inside the mouth. Gum health and disease can have an effect on general health. Structure The gums are part of the soft tissue l ...
, nitroglycerine, vaginal suppositories.


Topical

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 A topical medication is a medication that is applied to a particular place on or in the body. Most often topical medication means application to body surfaces such as the skin or mucous membranes to treat ailments via a large range of classes ...
also includes transdermal application, where the substance is administered onto the skin but is absorbed into the body to attain
systemic Systemic fundamental to a predominant social, economic, or political practice. This refers to: In medicine In medicine, ''systemic'' means affecting the whole body, or at least multiple organ systems. It is in contrast with ''topical'' or ''loc ...
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 such medication is the antibiotic
vancomycin Vancomycin is a glycopeptide antibiotic medication used to treat a number of bacterial infections. It is recommended intravenously as a treatment for complicated skin infections, bloodstream infections, endocarditis, bone and joint infection ...
, which cannot be absorbed in the gastrointestinal tract and is used orally only as a treatment for ''Clostridium difficile'' colitis.


Choice of routes

The reason for choice of routes of drug administration are governing 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 Emergency medicine is the Medical specialty, medical speciality concerned with the care of illnesses or Injury, injuries requiring immediate medical attention. Emergency physicians (often called “ER doctors” in the United States) continuous ...
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 Sterile or sterility may refer to: *Asepsis Asepsis is the state of being free from disease-causing micro-organisms (such as pathogenic bacteria, viruses, pathogenic fungi, and parasites). There are two categories of asepsis: medical and surgi ...
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 Naloxone, sold under the brand names Narcan (4 mg) and Kloxxado (8 mg) among others, is a medication used to reverse or reduce the effects of opioids. It is commonly used to counter decreased breathing in opioid overdose. Effects begin withi ...
(Narcan), an antagonist of opiates such as
morphine Morphine is a strong opiate that is found naturally in opium, a dark brown resin in poppies ('' Papaver somniferum''). It is mainly used as a pain medication, and is also commonly used recreationally, or to make other illicit opioids. T ...
. Naloxone counteracts opiate action in the
central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all p ...
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. However, some drugs can cause gastrointestinal tract irritation. 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. The oral route is limited to formulations containing small molecules only while biopharmaceuticals (usually proteins) would be digested in the stomach and thereby become ineffective. Biopharmaceuticals have to be given by injection or infusion. However, recent research (2018) found an organic ionic liquid suitable for oral
insulin Insulin (, from Latin ''insula'', 'island') is a peptide hormone produced by beta cells of the pancreatic islets encoded in humans by the ''INS'' gene. It is considered to be the main anabolic hormone of the body. It regulates the metabolism ...
delivery (a biopharmaceutical) into the blood stream.
Oral administration Oral administration is a route of administration where a substance is taken through the mouth. Per os abbreviated to P.O. is sometimes used as a direction for medication to be taken orally. Many medications are taken orally because they are ...
is often denoted "PO" from "per os", the Latin for "by mouth". The bioavailability of oral administration is affected by the amount of drug that is absorbed across the
intestinal epithelium The intestinal epithelium is the single cell layer that form the luminal surface (lining) of both the small and large intestine (colon) of the gastrointestinal tract. Composed of simple columnar epithelial cells, it serves two main functi ...
and first-pass metabolism.


Local

By delivering drugs almost directly to the site of action, the risk of systemic
side effects In medicine, a side effect is an effect, whether therapeutic or adverse, that is secondary to the one intended; although the term is predominantly employed to describe adverse effects, it can also apply to beneficial, but unintended, consequenc ...
is reduced. Skin absorption (dermal absorption), for example, is to directly deliver drug to the skin and, hopefully, to the systemic circulation. However, skin irritation may result, and for some forms such as creams or lotions, the dosage is difficult to control. Upon contact with the skin, the drug penetrates into the dead
stratum corneum The stratum corneum (Latin for 'horny layer') is the outermost layer of the epidermis. The human stratum corneum comprises several levels of flattened corneocytes that are divided into two layers: the ''stratum disjunctum'' and ''stratum compa ...
and can afterwards reach the viable
epidermis The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the amount of water rel ...
, the
dermis The dermis or corium is a layer of skin between the epidermis (with which it makes up the cutis) and subcutaneous tissues, that primarily consists of dense irregular connective tissue and cushions the body from stress and strain. It is divided ...
, and the
blood vessel The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide awa ...
s.


Mouth inhalation

Inhaled medications can be absorbed quickly and act both locally and systemically. Proper technique with inhaler devices is necessary to achieve the correct dose. Some medications can have an unpleasant taste or irritate the mouth. In general, only 20–50% of the pulmonary-delivered dose rendered in powdery particles will be deposited in the lung upon mouth inhalation. The remainder of 50-70% undeposited aerosolized particles are cleared out of lung as soon as exhalation. An inhaled powdery particle that is >8 μm is structurally predisposed to depositing in the central and conducting airways ( conducting zone) by inertial impaction. An inhaled powdery particle that is between 3 and 8 μm in diameter tend to largely deposit in the
transitional zone Transition or transitional may refer to: Mathematics, science, and technology Biology * Transition (genetics), a point mutation that changes a purine nucleotide to another purine (A ↔ G) or a pyrimidine nucleotide to another pyrimidine (C ↔ ...
s of the lung by sedimentation. An inhaled powdery particle that is <3 μm in diameter is structurally predisposed to depositing primarily in the
respiratory region The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies gr ...
s of the peripheral lung via diffusion. Particles that deposit in the upper and central airways are generally absorbed systemically to great extent because they are only partially removed by mucociliary clearance, which results in orally mediated absorption when the transported mucous is swallowed, and first pass metabolism or incomplete absorption through loss at the fecal route can sometimes reduce the bioavailability. 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.


Nasal inhalation

Inhalation by nose of a substance is almost identical to oral inhalation, except that some of the drug is absorbed intranasally instead of in the oral cavity before entering the airways. Both methods can result in varying levels of the substance to be deposited in their respective initial cavities, and the level of mucous in either of these cavities will reflect the amount of substance swallowed. The rate of inhalation will usually determine the amount of the substance which enters the lungs. Faster inhalation results in more rapid absorption because more substance finds the lungs. Substances in a form that resists absorption in the lung will likely resist absorption in the nasal passage, and the oral cavity, and are often even more resistant to absorption after they fail absorption in the former cavities and are swallowed.


Parenteral

The term parenteral is from para-1 ‘beside’ + Greek enteron ‘intestine’ + -al. This name is due to the fact that it encompasses a route of administration that is not intestinal. However, in common English the term has mostly been used to describe the 4 most well-known routes of injection. The term injection encompasses intravenous (IV),
intramuscular Intramuscular injection, often abbreviated IM, is the injection of a substance into a muscle. In medicine, it is one of several methods for parenteral administration of medications. Intramuscular injection may be preferred because muscles ha ...
(IM), subcutaneous (SC) and
intradermal Intradermal injection, often abbreviated ID, is a shallow or superficial injection of a substance into the dermis, which is located between the epidermis and the hypodermis. For certain substances, administration via an ID route can result in a ...
(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
antipsychotic Antipsychotics, also known as neuroleptics, are a class of psychotropic medication primarily used to manage psychosis (including delusions, hallucinations, paranoia or disordered thought), principally in schizophrenia but also in a range of ...
s, can be administered as long-acting intramuscular injections. The practice is often carried out through physical force in company of law-enforcement, and often against the will of the patient. However, all doses of long-acting antipsychotics injections are of at extreme risk to the health and well-being of the patient. Extreme ethical concerns should be considered. If the choice is made to use force, care should be taken to use only the smallest dose that is currently scientifically demonstrated to be efficacious for the specific drug. This is because, despite being injected, the drugs are designed with heavy esterifying molecular additions which can cause traces of the drugs to be found in circulation for up to one year. Ongoing
IV infusion Intravenous therapy (abbreviated as IV therapy) is a medical technique that administers fluids, medications and nutrients directly into a person's vein. The intravenous route of administration is commonly used for rehydration or to provide nutrie ...
s 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. However, in some cases, patients are taught to self-inject, such as SC injection of insulin in patients with
insulin-dependent diabetes mellitus Type 1 diabetes (T1D), formerly known as juvenile diabetes, is an autoimmune disease that originates when cells that make insulin (beta cells) are destroyed by the immune system. Insulin is a hormone required for the cells to use blood sugar f ...
. As the drug is delivered to the site of action extremely rapidly with IV injection, there is a risk of overdose if the dose has been calculated incorrectly, and there is an increased risk of side effects if the drug is administered too rapidly.


Intranasal

Drug administration via the nasal cavity yields rapid drug absorption and therapeutic effects. This is because drug absorption through the nasal passages doesn't 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 The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all p ...
via the pathways of
olfactory The sense of smell, or olfaction, is the special sense through which smells (or odors) are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste. In humans, ...
and
trigeminal nerve In neuroanatomy, the trigeminal nerve ( lit. ''triplet'' nerve), also known as the fifth cranial nerve, cranial nerve V, or simply CN V, is a cranial nerve responsible for sensation in the face and motor functions such as biting and che ...
. Intranasal absorption features low lipophilicity, enzymatic degradation within the nasal cavity, large molecular size, and rapid mucociliary clearance from the nasal passages, which explains the low risk of systemic exposure of the administered drug absorbed via intranasal.


Sublingual

Sublingual administration is fulfilled by placing the drug between the tongue and the lower surface of the mouth. The
sublingual mucosa Sublingual (abbreviated SL), from the Latin for "under the tongue", refers to the pharmacological route of administration by which substances diffuse into the blood through tissues under the tongue. The sublingual glands receive their prim ...
is highly permeable and thereby provides access to the underlying expansive network composed of capillaries, leading to rapid drug absorption.


Buccal

Buccally administered medication is achieved by placing the drug between
gums The gums or gingiva (plural: ''gingivae'') consist of the mucosal tissue that lies over the mandible and maxilla inside the mouth. Gum health and disease can have an effect on general health. Structure The gums are part of the soft tissue li ...
and the inner lining of the cheek. In comparison with sublingual tissue, buccal tissue is less permeable resulting in slower
absorption Absorption may refer to: Chemistry and biology *Absorption (biology), digestion **Absorption (small intestine) *Absorption (chemistry), diffusion of particles of gas or liquid into liquid or solid materials *Absorption (skin), a route by which s ...
.


Sublabial administration

Sublabial administration


Research

Neural drug delivery is the next step beyond the basic addition of growth factors to nerve guidance conduits. Drug delivery systems allow the rate of growth factor release to be regulated over time, which is critical for creating an environment more closely representative of in vivo development environments.Lavik, E. and R. Langer, Tissue engineering; current state and perspectives. Applied Microbiology Biotechnology, 2004. 65: p. 1-8


See also

* ADME * Catheter * Dosage form * Drug injection *
Ear instillation Ear instillation is the process of introducing otic medication or other liquids into the ear canal. Proper care is needed in delivering such liquids. Indications for ear instillation * patients with otitis media * patients with otitis externa * ...
*
Hypodermic needle A hypodermic needle (from Greek ὑπο- (''hypo-'' = under), and δέρμα (''derma'' = skin)), one of a category of medical tools which enter the skin, called sharps, is a very thin, hollow tube with one sharp tip. It is commonly used ...
*
Intravenous marijuana syndrome Intravenous marijuana syndrome is a distinct short-term clinical syndrome related to the intravenous injection of boiled cannabis broth, which had been filtered through a cotton cloth. The syndrome has at least 25 known cases in the English langua ...
*
List of medical inhalants {{Short description, none Drugs and therapeutic agents administered by inhalation Inhalational anesthetic agents * aliflurane * chloroform * cyclopropane * desflurane * diethyl ether * halothane * isoflurane * methoxyflurane * methoxypropane * nit ...
* Nanomedicine * Absorption (pharmacology)


References


External links


The 10th US-Japan Symposium on Drug Delivery Systems


* [https://www.fda.gov/Drugs/DevelopmentApprovalProcess/FormsSubmissionRequirements/ElectronicSubmissions/DataStandardsManualmonographs/ucm071666.htm FDA Center for Drug Evaluation and Research Data Standards Manual: Dosage Form.]
A.S.P.E.N. American Society for Parenteral and Enteral Nutrition
* {{DEFAULTSORT:Route Of Administration Drugs Pharmacokinetics Routes of administration