Clemastine
Encyclopedia
Clemastine, also known as meclastin, is an antihistamine
and anticholinergic
. Unlike loratadine
or fexofenadine
, clemastine is a sedating antihistamine, however it exhibits fewer other side effects than most of the widely used antihistamines. Clemastine is also classified as an antipruritic
(i.e. it stops itching).
and sedative
effects. Antihistamines competitively bind to histamine
receptor sites, thus reducing the neurotransmitter's effects. Effects of histamine (which are countered by antihistamines) include:
Clemastine inhibits both the vasoconstrictor and vasodilator effects of histamine. Depending on the dose, the drug can produce paradoxical effects, including CNS stimulation or depression.
Most antihistamines exhibit some type of anticholinergic
activity. Antihistamines act by competitively binding to H1- receptor sites, thus blocking the binding endogenous histamine. Antihistamines do not chemically inactivate or prevent the normal release of histamine.
Clemastine is rapidly absorbed from the gastrointestinal tract
and peak plasma concentrations are attained in 2-4 hours.
histamine, which leads to temporary relief of the negative symptoms caused by histamine.
, such as sneezing, rhinorrhea
, pruritus and lacrimation.
Germany - In Germany sold under the brand name Tavegil.
Sweden - In Sweden it is sold under the brand name of Tavegyl and unlike the newer non-sedative antihistamines used for allergy, prescription only.
Turkey - Sold under the brand name Tavegyl by Novartis.
depression to stimulation. Stimulation is most common in children, and is usually followed by excitement, hallucinations, ataxia
, incoordination, muscle twitching, athetosis
, hyperthermia
, cyanosis
convulsions, tremors, and hyperreflexia
. This may be followed by postictal depression and cardiovascular/respiratory arrest. Other common overdose symptoms include dry mouth, fixed dilated pupils, flushing of the face, and pyrexia. In adults, overdose usually leads to CNS depression, ranging from drowsiness to coma.
The oral LD50 of clemastine in the rat and mouse is 3550 mg/kg and 730 mg/kg, respectively.
Antihistamine
An H1 antagonist is a histamine antagonist of the H1 receptor that serves to reduce or eliminate effects mediated by histamine, an endogenous chemical mediator released during allergic reactions...
and anticholinergic
Anticholinergic
An anticholinergic agent is a substance that blocks the neurotransmitter acetylcholine in the central and the peripheral nervous system. An example of an anticholinergic is dicycloverine, and the classic example is atropine....
. Unlike loratadine
Loratadine
Loratadine is a second-generation H1 histamine antagonist drug used to treat allergies. Structurally, it is closely related to tricyclic antidepressants such as imipramine, and distantly related to the atypical antipsychotic quetiapine. It is marketed by Schering-Plough under several trade names...
or fexofenadine
Fexofenadine
Fexofenadine is an antihistamine drug used in the treatment of hayfever and similar allergy symptoms...
, clemastine is a sedating antihistamine, however it exhibits fewer other side effects than most of the widely used antihistamines. Clemastine is also classified as an antipruritic
Antipruritic
Antipruritics, also known as anti-itch drugs, are medications that inhibit the itching that is often associated with sunburns, allergic reactions, eczema, psoriasis, chickenpox, fungal infections, insect bites and stings like those from mosquitoes, fleas, and mites, and contact dermatitis and...
(i.e. it stops itching).
Pharmacology
Clemastine is an antihistamine with anticholinergicAnticholinergic
An anticholinergic agent is a substance that blocks the neurotransmitter acetylcholine in the central and the peripheral nervous system. An example of an anticholinergic is dicycloverine, and the classic example is atropine....
and sedative
Sedative
A sedative or tranquilizer is a substance that induces sedation by reducing irritability or excitement....
effects. Antihistamines competitively bind to histamine
Histamine
Histamine is an organic nitrogen compound involved in local immune responses as well as regulating physiological function in the gut and acting as a neurotransmitter. Histamine triggers the inflammatory response. As part of an immune response to foreign pathogens, histamine is produced by...
receptor sites, thus reducing the neurotransmitter's effects. Effects of histamine (which are countered by antihistamines) include:
- Increased capillary permeability
- Increased capillary dilatation
- EdemaEdemaEdema or oedema ; both words from the Greek , oídēma "swelling"), formerly known as dropsy or hydropsy, is an abnormal accumulation of fluid beneath the skin or in one or more cavities of the body that produces swelling...
(i.e. swelling) - Pruritus (Itch)
- Gastrointestinal/respiratory smooth muscle constriction
Clemastine inhibits both the vasoconstrictor and vasodilator effects of histamine. Depending on the dose, the drug can produce paradoxical effects, including CNS stimulation or depression.
Most antihistamines exhibit some type of anticholinergic
Anticholinergic
An anticholinergic agent is a substance that blocks the neurotransmitter acetylcholine in the central and the peripheral nervous system. An example of an anticholinergic is dicycloverine, and the classic example is atropine....
activity. Antihistamines act by competitively binding to H1- receptor sites, thus blocking the binding endogenous histamine. Antihistamines do not chemically inactivate or prevent the normal release of histamine.
Clemastine is rapidly absorbed from 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. ....
and peak plasma concentrations are attained in 2-4 hours.
Mechanism of Action
Clemastine is a selective histamine H1 antagonist. It binds to the histamine H1 receptor, thus blocking the action of endogenousEndogenous
Endogenous substances are those that originate from within an organism, tissue, or cell. Endogenous retroviruses are caused by ancient infections of germ cells in humans, mammals and other vertebrates...
histamine, which leads to temporary relief of the negative symptoms caused by histamine.
Metabolism
Antihistamines are thought to be metabolized in the liver, mostly by mono-/didemethylation and glucuronide conjugation. It is an inhibitor of cytochrome P450 2D6 and may interfere with other drugs metabolized by this isozyme.Indications
Clemastine is indicated for use in treating allergic rhinitisRhinitis
Rhinitis , commonly known as a stuffy nose, is the medical term describing irritation and inflammation of some internal areas of the nose. The primary symptom of rhinitis is nasal dripping. It is caused by chronic or acute inflammation of the mucous membrane of the nose due to viruses, bacteria or...
, such as sneezing, rhinorrhea
Rhinorrhea
Rhinorrhea or rhinorrhoea is a condition where the nasal cavity is filled with a significant amount of mucous fluid. The condition, commonly known as "runny nose", occurs relatively frequently and is not usually considered dangerous. Rhinorrhea is a common symptom of allergies or certain diseases,...
, pruritus and lacrimation.
Availability
Clemastine is an OTC drug, and is available as a syrup (0.5 mg per 5mL) and tablet (1mg). It is sold in the United States under the brand name Tavist.Brand Names in other countries
Brasil - In Brasil it is sold under the brand name of Agasten by Novartis.Germany - In Germany sold under the brand name Tavegil.
Sweden - In Sweden it is sold under the brand name of Tavegyl and unlike the newer non-sedative antihistamines used for allergy, prescription only.
Turkey - Sold under the brand name Tavegyl by Novartis.
Toxicity
Overdosage symptoms are paradoxical, ranging from CNSCentral nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
depression to stimulation. Stimulation is most common in children, and is usually followed by excitement, hallucinations, ataxia
Ataxia
Ataxia is a neurological sign and symptom that consists of gross lack of coordination of muscle movements. Ataxia is a non-specific clinical manifestation implying dysfunction of the parts of the nervous system that coordinate movement, such as the cerebellum...
, incoordination, muscle twitching, athetosis
Athetosis
Athetosis is a symptom characterized by involuntary convoluted, writhing movements of the fingers, arms, legs, and neck. Movements typical of athetosis are sometimes called athetoid movements. Lesions to the brain are most often the direct cause of the symptoms, particularly to thecorpus striatum...
, hyperthermia
Hyperthermia
Hyperthermia is an elevated body temperature due to failed thermoregulation. Hyperthermia occurs when the body produces or absorbs more heat than it can dissipate...
, cyanosis
Cyanosis
Cyanosis is the appearance of a blue or purple coloration of the skin or mucous membranes due to the tissues near the skin surface being low on oxygen. The onset of cyanosis is 2.5 g/dL of deoxyhemoglobin. The bluish color is more readily apparent in those with high hemoglobin counts than it is...
convulsions, tremors, and hyperreflexia
Hyperreflexia
Hyperreflexia is defined as overactive or overresponsive reflexes. Examples of this can include twitching or spastic tendencies, which are indicative of upper motor neuron disease as well as the lessening or loss of control ordinarily exerted by higher brain centers of lower neural pathways...
. This may be followed by postictal depression and cardiovascular/respiratory arrest. Other common overdose symptoms include dry mouth, fixed dilated pupils, flushing of the face, and pyrexia. In adults, overdose usually leads to CNS depression, ranging from drowsiness to coma.
The oral LD50 of clemastine in the rat and mouse is 3550 mg/kg and 730 mg/kg, respectively.