Diphenhydramine

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Diphenhydramine

Diphenhydramine hydrochloride , trade name Benadryl
Benadryl

Benadryl, is a brand name allergy medicine manufactured by McNeil Healthcare Limited. Benadryl is used as an antihistamine for the temporary relief of seasonal and perennial allergy symptoms....
as produced by McNeil-PPC

McNeil Laboratories

McNeil Consumer Healthcare is an American pharmaceutical company and a subsidiary of Johnson & Johnson....
a division of Johnson & Johnson, or Dimedrol outside the U.S. & Canada. It is also found in the name-brand products Nytol
Nytol

File:Nytol UK.jpgNytol is a brand of sleeping pill produced by GlaxoSmithKline. The active ingredient is Diphenhydramine Hydrochloride, which is a type of medicine called a sedating antihistamine....
and Unisom

Unisom

Doxylamine

Over-the-counter drug

Over-the-counter drugs are medications that may be sold to a customer without a medical prescription. The term "over-the-counter" is somewhat counter-intuitive, since these items can often be found on the shelves of stores and bought like any other packaged product in some countries in contrast to prescription drug which are more likely to l...
(OTC) or prescribed HCI injectable; mainly used as an antihistamine

Antihistamine

Antiemetic

An antiemetic is a medication that is effective against vomiting and nausea. Anti-emetics are typically used to treat motion sickness and the Adverse effect of opioid analgesics, general anaesthetics and chemotherapy directed against cancer....
, sedative

Sedative

A sedative is a substance that induces sedation by reducing irritability or excitement.At higher doses it may result in slurred speech, staggering gait , poor judgment, and slow, uncertain reflexes....
, and hypnotic

Hypnotic

Hypnotic drugs induce sleep, used in the treatment of insomnia and in surgical anesthesia. Because drugs in this class generally produce dose-dependent effects, ranging from anxiolysis to production of unconsciousness, they are often referred to collectively as sedative-hypnotic drugs....
. It may also be used for the treatment of extrapyramidal side effects of typical antipsychotic

Typical antipsychotic

Typical antipsychotics are a class of antipsychotic drugs first developed in the 1950s and used to treat psychosis , and are generally being replaced by atypical antipsychotic drugs....
s, such as the tremors that haloperidol

Haloperidol

Haloperidol is a typical antipsychotic. It is in the butyrophenone class of antipsychotic medications and has pharmacology similar to the phenothiazines....
can cause.

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Encyclopedia

McNeil Laboratories

Unisom

Doxylamine

Over-the-counter drug

Antihistamine

Antiemetic

Sedative

Hypnotic

Typical antipsychotic

Haloperidol

Haloperidol is a typical antipsychotic. It is in the butyrophenone class of antipsychotic medications and has pharmacology similar to the phenothiazines....
can cause. Additionally, injectable diphenhydramine can be used for life threatening reactions (anaphylaxis

Anaphylaxis

Anaphylaxis is an acute Circulatory system and very severe Type I hypersensitivity allergy reaction in humans and other mammals. The term comes from the Greek words a?a ana and f??a??? phylaxis ....
) to allergens such as bee stings, peanuts, or latex rather than risking the side effects of epinephrine

Epinephrine

Epinephrine is a hormone and neurotransmitter.Epinephrine increases the "fight or flight" response of the Sympathetic nervous system of the autonomic nervous system....
. It is a member of the ethanolamine

Ethanolamine

Ethanolamine, also called 2-aminoethanol or monoethanolamine , is an organic chemical compound that is both a primary amine and a primary alcohol ....
class of antihistaminergic agents.

Diphenhydramine is also an anticholinergic

Anticholinergic

An anticholinergic agent is a substance that blocks the neurotransmitter acetylcholine in the central nervous system and the peripheral nervous system....
and was discovered during the search for synthetic alternatives to scopolamine

Scopolamine

Scopolamine, known by the names levo-duboisine and hyoscine, is a tropane alkaloid Medication with muscarinic antagonist effects. It is obtained from plants of the family Solanaceae , such as henbane, jimson weed and Angel's Trumpets , and corkwood ....
which would be easier to work with.

Diphenhydramine was one of the first known antihistamines, invented in 1943 by Dr. George Rieveschl

George Rieveschl

Dr. George Rieveschl was an United States chemist and professor. He was the inventor of the popular antihistamine diphenhydramine , which he first made during a search for synthetic alternatives to scopolamine....
, a former professor at the University of Cincinnati

University of Cincinnati

The University of Cincinnati is a coeducational public university research university in Cincinnati, Ohio, Ohio, part of the University System of Ohio....
. It became the first FDA-approved prescription antihistamine in 1946.

The brand Benadryl is currently trademark

TradeMark

TradeMark is a tall, primarily residential, skyscraper in Charlotte, North Carolina. It was completed in 2007 and has 28 floors. There are 200 hundred residential units....
ed in the United States

United States

The United States of America is a Federal government constitutional republic comprising U.S. state and a federal district. The country is situated mostly in central North America, where its Contiguous United States and Washington, D.C., the Capital districts and territories, lie between the Pacific Ocean and Atlantic Oceans, Borders of the U...
by Pfizer

Pfizer

Pfizer Incorporated is a major pharmaceutical company, ranking number one in sales in the world. The company is based in New York City, and its research headquarters is in Groton, Connecticut....
; however, many drug store chains and retail outlets manufacture less-costly generic versions

Generic drug

A generic drug is a medication which isproduced and distributed without patent protection. The generic drug may still have a patent on the formulation but not on the active ingredient....
under their own store brands.

Pharmacological action

Diphenhydramine works by blocking the effect of histamine at H₁ receptor

Transmembrane receptor

Transmembrane receptors are integral membrane proteins, which reside and operate typically within a cell's plasma membrane, but also in the biological membrane of some subcellular compartments and organelles....
sites. This results in effects such as the increase of vascular smooth muscle

Smooth muscle

Smooth muscle is a type of non-striated muscle, found within the tunica media layer of large and small arteries and veins, the urinary bladder, uterus, male and female reproductive tracts, gastrointestinal tract, respiratory tract, the ciliary muscle, and iris of the eye....
contraction, thus reducing the redness, hyperthermia and edema that occurs during an inflammatory reaction. In addition, by blocking the H1 receptor on peripheral nociceptors, diphenhydramine decreases their sensitization and consequently reduces itching that is associated with an allergic reaction. This is why diphenhydramine a popular choice for treatment of the symptoms of allergic rhinitis

Hay Fever

Hay Fever is a comic play written by No?l Coward in 1924 and first produced in 1925 with Marie Tempest as the first Judith Bliss. Best described as a cross between high farce and a comedy of manners, the play is set in an English country house in the 1920s, and deals with the four eccentric members of the Bliss family and their outlandish b...
, hives, motion sickness

Motion sickness

Motion sickness or kinetosis is a condition in which a disagreement exists between visually perceived movement and the vestibular system's sense of movement....
, and insect bites and stings.

In the 1960s it was found that diphenhydramine inhibits reuptake

Reuptake

Reuptake, or re-uptake, is the reabsorption of a neurotransmitter by a neurotransmitter transporter of a Synapse neuron after it has performed its function of transmitting a Action potential....
of the neurotransmitter

Neurotransmitter

Neurotransmitters are chemistry which relay, amplify and modulate signals between a neuron and another cell . Neurotransmitters are packaged into vesicles that cluster beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to receptors in the membrane on the postsynaptic side of...
serotonin

Serotonin

Serotonin is a monoamine neurotransmitter synthesized in serotonergic neurons in the central nervous system and enterochromaffin cells in the gastrointestinal tract of animals including humans....
. This discovery led to a search for viable antidepressant

Antidepressant

An antidepressant is a psychiatric medication used for alleviating major depressive disorder or dysthymia. Drug groups known as MAOIs, tricyclics, and second-generation antidepressants such as SSRIs, and serotonin-norepinephrine reuptake inhibitors are particularly associated with the term....
s with similar structures and fewer side effects, culminating in the invention of fluoxetine

Fluoxetine

Fluoxetine hydrochloride is an antidepressant of the selective serotonin reuptake inhibitor class. Fluoxetine is approved for the treatment of major depressive disorder , obsessive-compulsive disorder , bulimia nervosa, anorexia nervosa, panic disorder and premenstrual dysphoric disorder....
(Prozac), a selective serotonin reuptake inhibitor

Selective serotonin reuptake inhibitor

Selective serotonin reuptake inhibitors or serotonin-specific reuptake inhibitor are a class of antidepressants used in the treatment of Clinical depression, anxiety disorders, and some personality disorders....
(SSRI). A similar search had previously led to the synthesis of the first SSRI zimelidine

Zimelidine

Zimelidine was the first selective serotonin reuptake inhibitor antidepressant to be marketed. It is a pyridylallylamine, and is structurally different from other antidepressants....
from brompheniramine

Brompheniramine

Brompheniramine , commonly marketed as its salt brompheniramine maleate is an antihistamine drug of the propylamine class. It is commonly available Over-the-counter drug and is indicated for the treatment of the symptoms of the common cold and allergic rhinitis, such as runny nose, itchy eyes, watery eyes, and sneezing....
, also an antihistamine.

Common use and dosage

As an antihistamine, recommended doses for adults is 25-50 mg diphenhydramine every 4-6 hours, not to exceed 50-100 mg every 4-6 hours.

Diphenhydramine is a first-generation antihistamine

Antihistamine

An H1 antagonist is a histamine antagonist of the histamine H1 receptor that serves to reduce or eliminate effects mediated by histamine, an endogenous chemical mediator released during allergy....
drug. Despite being one of the oldest antihistamines on the market, it is largely the most effective antihistamine available either by prescription or over-the-counter, and has been shown to exceed the effectiveness of even the latest prescription drugs. Consequently, it is frequently used when an allergic reaction requires fast, effective reversal of the often dangerous effects of a massive histamine release.

Diphenhydramine has sedative

Sedative

Unisom

Doxylamine

Doxylamine succinate is one of the many sedating antihistamines used by itself as a short-term sedative, in combination with other drugs as a night-time common cold and allergy relief drug, and a preparation is prescribed in combination with vitamin B6 to prevent morning sickness in pregnancy women....
, a different active ingredient), and most notably Tylenol PM where it is combined with acetaminophen (paracetamol), Nytol and the US version of Sominex (not to be confused with the UK version which uses promethazine

Promethazine

Promethazine is a first-generation histamine H1 receptor antagonist, antihistamine and antiemetic medication. It can also have strong sedative effects although it is rarely used specifically for this....
) which have diphenhydramine as the only active ingredient. Several generic and store brands of antihistamines and sleep aids also contain solely diphenhydramine, such as Tylenol Simply Sleep.

Diphenhydramine is widely used in nonprescription

Over-the-counter drug

Over-the-counter drugs are medications that may be sold to a customer without a medical prescription. The term "over-the-counter" is somewhat counter-intuitive, since these items can often be found on the shelves of stores and bought like any other packaged product in some countries in contrast to prescription drug which are more likely to l...
sleep aids with a maximum recommended dose of 50 mg (as the hydrochloride

Hydrochloride

In chemistry, hydrochlorides are salt s resulting, or regarded as resulting, from the reaction of hydrochloric acid with an organic Base . This is also known as muriate, derived from hydrochloric acid's other name: muriatic acid....
salt) being mandated by the FDA. In the United Kingdom

United Kingdom

The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom , the UK or Britain,is a sovereign state located off the northwestern coast of continental Europe....
, Australia

Australia

Australia, officially the Commonwealth of Australia, is a country in the southern hemisphere comprising the Australia of the world's smallest continent, the major island of Tasmania, and numerous list of islands of Australia in the Indian Ocean and Pacific Oceans....
, New Zealand

New Zealand

New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses , and numerous Islands of New Zealand, most notably Stewart Island/Rakiura and the Chatham Islands....
, South Africa

South Africa

The Republic of South Africa, also known by Official names of South Africa, is a country located at the southern tip of the continent of Africa....
, and other countries, a 50 to 100 mg recommended dose is permitted, though in the case of New Zealand the purchaser is required to provide the pharmacist with their name, address and other personal identification to be later logged in a national police data base following any purchase of over the counter medications containing diphenhydramine such as Unisom

Unisom

Unisom is the Chattem brand name for an Over-the-counter drug sleep-aid medication. While marketed under a single trademark, the active ingredient may be one of two drugs, depending on the type of preparation....
.

There are also topical formulations of diphenhydramine available, including creams, lotions, gels, and sprays. They are used to relieve itching, and have the advantage of causing much less systemic effect (i.e. drowsiness) than oral forms.

Side effects

Like many other first-generation antihistamines, diphenhydramine is a potent anticholinergic

Anticholinergic

An anticholinergic agent is a substance that blocks the neurotransmitter acetylcholine in the central nervous system and the peripheral nervous system....
agent. This leads to profound drowsiness as a very common side-effect, along with the possibilities of motor impairment (ataxia

Ataxia

Ataxia is a neurology sign and symptom consisting of gross lack of coordination of muscle movements. Ataxia is a non-specific clinical manifestation implying dysfunction of parts of the nervous system that coordinate movement, such as the cerebellum....
), dry mouth and throat, flushed skin, rapid or irregular heartbeat (tachycardia

Tachycardia

The word tachycardia comes from the Greek words tachys and kardia .Tachycardia typically refers to a heartrate that exceeds the range of the normal resting heartrate, based upon age:...
), blurred vision at nearpoint owing to lack of accommodation (cycloplegia

Cycloplegia

Cycloplegia is paralysis of the ciliary muscle of the eye, resulting in a loss of accommodation . ...
), abnormal sensitivity to bright light (photophobia

Photophobia

Photophobia is a symptom of excessive sensitivity to light and the aversion to sunlight or well-lit places. In medical terms it is not fear, but an experience of discomfort or pain to the eyes due to light exposure....
), pupil dilation (mydriasis

Mydriasis

Mydriasis is an excessive dilation of the pupil due to disease, Physical trauma, or the use of drugs. Normally, the pupil dilates in the dark and constriction in the light to improve vividity at night and to protect the retina from sunlight damage during the day....
), urinary retention (ischuria), constipation, difficulty concentrating, short-term memory loss, visual disturbances, hallucinations, irritability, itchy skin, confusion, erectile dysfunction, and delirium. Some side effects such as twitching may be delayed until the drowsiness begins to cease and the person is in more of an awakening mode. Diphenhydramine also has local anesthetic

Local anesthetic

A local anesthetic is a medication that causes reversible local anesthesia and a loss of nociception. When it is used on specific nerve pathways , effects such as analgesia and paralysis can be achieved....
properties, and has been used for patients allergic to common local anesthetics like lidocaine

Lidocaine

Lidocaine or lignocaine is a common local anesthetic and antiarrhythmic agent drug. Lidocaine is used topically to relieve itching, burning and pain from skin inflammations, injected as a dental anesthetic, and in minor surgery....
. Severe, prolonged twitching and muscle spasm have also been experienced.

The most common cardiac dysrhythmias associated with diphenhydramine overdose are sinus bradycardia, elongated S-T segment interval, and premature ventricular contraction

Premature ventricular contraction

A Premature Ventricular Contraction , also known as a ventricular premature beat or extrasystole, is a relatively common event where the heart rate is initiated by the heart ventricles rather than by the sinoatrial node, the normal heartbeat initiator....
.

Diphenhydramine is similar in its effects to dimenhydrinate

Dimenhydrinate

Dimenhydrinate is an over-the-counter drug used to prevent nausea and motion sickness. It is marketed in Portugal as Viabom, but in prescription format....
(Dramamine), its 8-chlorotheophylline

8-Chlorotheophylline

8-Chlorotheophylline is a xanthine derivative with stimulant properties. It is combined with pharmaceutical drugs to form stable salts, such as dimenhydrinate....
salt, although the latter is approximately 60% the potency in terms of required dosage and is slightly less sedating.

Some patients have an allergic reaction to diphenhydramine in the form of hives.

Since 2002 the US FDA requires special labeling: avoid using multiple products including diphenhydramine, or using topical forms to treat poison ivy urushiol-induced contact dermatitis

Urushiol-induced contact dermatitis

Urushiol-induced contact dermatitis is the medical name given to allergy rashes produced by the oil urushiol, which is contained in various plants, including the plants of the genus Toxicodendron , as well as other plants in the family Anacardiaceae , and also unrelated plants such as Ginkgo biloba....
.

Diphenhydramine has shown to build tolerance against its sedation effectiveness very quickly, with placebo-like results after a 3rd day of common dosage.

Recreational use

Diphenhydramine is used both clinically and/or recreationally in conjunction with opioids to relieve itching and act as an analgesia potentiator

Potentiator

In clinical terms, a potentiator is a reagent that enhances sensitization of an antigen. Potentiators are used in the clinical laboratory for performing blood banking procedures that require enhancement of agglutination in order to detect the presence of antibodies or antigens in a patient's blood sample....
.

It is used recreationally as a deliriant

Deliriant

The deliriants are a special class of acetylcholine receptor-inhibitor dissociatives. The name comes from their primary effect of inducing a medical state of frank delirium, characterized by stupor, utter confusion, confabulation, and regression to "phantom" behaviors such as disrobing and plucking ....
, depressant

Depressant

Depressant is a chemical agent that diminishes the function or activity of a specific part of the body.The term is used in particular with regard to the central nervous system ....
, in combination with dextromethorphan

Dextromethorphan

Dextromethorphan is an antitussive drug. It is one of the active ingredients used to prevent coughs in many Over-the-counter drug common cold and cough medicines....
, or booster for alcohol.

Diphenhydramine is a moderate CYP2D6

CYP2D6

Cytochrome P450 2D6 , a member of the cytochrome P450 mixed-function oxidase system, is one of the most important enzymes involved in the metabolism of xenobiotics in the body....
inhibitor, and as a result can cause increases in blood levels of drugs that are CYP2D6

CYP2D6

Cytochrome P450 2D6 , a member of the cytochrome P450 mixed-function oxidase system, is one of the most important enzymes involved in the metabolism of xenobiotics in the body....
substrates. Diphenhydramine can also have an additive effect with other CNS

Central nervous system

The central nervous system is the part of the nervous system that functions to coordinate the activity of all parts of the bodies of multicellular organisms....
depressants. Due to its interaction with a broad array of medications, combining diphenhydramine with other medications without medical supervision could have unanticipated and potentially hazardous results.

Many users report a side effect profile consistent with atropine

Atropine

Atropine is a tropane alkaloid extracted from deadly nightshade , jimsonweed , Mandrake and other plants of the family Solanaceae. It is a secondary metabolite of these plants and serves as a hard drug with a wide variety of effects....
intoxication. This is due to antagonism

Receptor antagonist

A receptor antagonist is a type of receptor ligand or drug that does not provoke a biological response itself upon binding to a Receptor , but blocks or dampens agonist-mediated responses....
of muscarinic acetylcholine

Acetylcholine

The chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including homo sapiens....
receptors in both the central

Central nervous system

The central nervous system is the part of the nervous system that functions to coordinate the activity of all parts of the bodies of multicellular organisms....
and autonomic nervous system

Autonomic nervous system

The autonomic nervous system is the part of the peripheral nervous system that acts as a control system, maintaining human homeostasis in the body....
which inhibits various signal transduction

Signal transduction

In biology, 'signal transduction' refers to any process by which a cell converts one kind of signal or stimulus into another. Most processes of signal transduction involve ordered sequences of biochemistry chemical reaction inside the cell, which are carried out by enzymes, activated by Second messenger systems, resulting in a signal tran...
pathways.

In the CNS

Central nervous system

The central nervous system is the part of the nervous system that functions to coordinate the activity of all parts of the bodies of multicellular organisms....
, diphenhydramine readily crosses the blood-brain barrier

Blood-brain barrier

The blood-brain barrier is a metabolic or cellular structure in the central nervous system that restricts the passage of various chemical substances and microscopic objects between the bloodstream and the neural tissue itself, while still allowing the passage of substances essential to metabolism function ....
, exerting effects within the visual

Visual cortex

The term visual cortex refers to the primary visual cortex and Extrastriate cortex such as V2, V3, V4, and V5....
and auditory cortex

Primary auditory cortex

The primary auditory cortex is the region of the brain that is responsible for processing of auditory system information....
. Other CNS

Central nervous system

The central nervous system is the part of the nervous system that functions to coordinate the activity of all parts of the bodies of multicellular organisms....
effects occur within the limbic system

Limbic system

The limbic system is a set of brain structures including the hippocampus, amygdala, anterior thalamic nuclei, and limbic cortex, which support a variety of functions including emotion, behavior, long term memory, and olfactory....
and hippocampus

Hippocampus

The hippocampus is a brain structure located inside the medial temporal lobe of the cerebral cortex, and therefore is part of the telencephalon ....
, causing confusion

ConFusion

ConFusion is an annual science fiction convention organized by the Stilyagi Air Corps and its parent organization, the Ann Arbor Science Fiction Association....
and temporary amnesia

Amnèsia

Amn?sia is an Italian language drama film directed by Gabriele Salvatores in 2002 in film.External links...
.

Toxicology also manifests in the autonomic nervous system

Autonomic nervous system

The autonomic nervous system is the part of the peripheral nervous system that acts as a control system, maintaining human homeostasis in the body....
, causing urinary retention

Urinary retention

Urinary retention also known as ischuria is a lack of ability to urinate. It is a common complication of Benign prostatic hyperplasia , although anticholinergics may also play a role, and requires a catheter or Prostatic stent....
, pupil dilation, tachycardia

Tachycardia

Urination

Urination, also known as micturition, voiding, and, more rarely, emiction, is the process of disposing urine from the urinary bladder through the urethra to the outside of the body....
, and dry skin and mucous membranes.

Considerable overdosage can lead to myocardial infarction

Myocardial infarction

Myocardial infarction , commonly known as a heart attack, occurs when the Blood flow to part of the heart is interrupted. This is most commonly due to occlusion of a coronary artery following the rupture of a Vulnerable plaque, which is an unstable collection of lipids and white blood cells in the wall of an artery....
(heart attack), serious ventricular dysrhythmias

Cardiac arrhythmia

Cardiac arrhythmia is a term for any of a large and heterogeneous group of conditions in which there is abnormal Electrical conduction system of the heart in the heart....
, coma

Coma

In medicine, a coma is a profound state of unconsciousness. A comatose person cannot be awakened, fails to respond normally to pain or light, does not have sleep-wake cycles, and does not take voluntary actions....
and death

Death

Death is the permanent termination of the biological functions that define a life organism. It refers to both a particular event and to the condition that results thereby....
.

Such a side-effect profile is thought to give ethanolamine

Ethanolamine

Ethanolamine, also called 2-aminoethanol or monoethanolamine , is an organic chemical compound that is both a primary amine and a primary alcohol ....
-class antihistamines a relatively low abuse liability.

The specific antidote for diphenhydramine poisoning is physostigmine

Physostigmine

Physostigmine is a parasympathomimetic, specifically, a reversible cholinesterase inhibitor alkaloid of the Calabar bean.The chemical was synthesized for the first time in 1935 by the chemists Percy Lavon Julian and Josef Pikl....
, usually given by IV in hospital.

External links

(PDF)
University of Maryland Medical Center - Includes comprehensive dosage recommendations
- suicide by Diphenhydramine - BBC News

Diphenhydramine

Pharmacological action

Common use and dosage

Side effects

Recreational use

See also

Sources

External links