Clemastine

Clemastine
Clinical data
AHFS/Drugs.com Monograph
MedlinePlus a682542
Pregnancy
category
  • US: B (No risk in non-human studies)
    Routes of
    administration    		 Oral
    ATC code
    Legal status
    Legal status
    Pharmacokinetic data
    Bioavailability 39.2%
    Metabolism Hepatic
    Elimination half-life 21.3 hours
    Excretion Renal
    Identifiers
    CAS Number
    PubChem CID
    IUPHAR/BPS
    DrugBank
    ChemSpider
    UNII
    KEGG
    ChEBI
    ChEMBL
    Chemical and physical data
    Formula C21H26ClNO
    Molar mass 343.9 g/mol
    3D model (JSmol)
      (verify)

    Clemastine, also known as meclastin, is an antihistamine and anticholinergic.[1] 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).

    Indications

    Clemastine is indicated for use in treating allergic rhinitis, such as sneezing, rhinorrhea, pruritus and lacrimation.

    Side effects

    Overdosage symptoms are paradoxical, ranging from CNS depression to stimulation. Stimulation is most common in children, and is usually followed by excitement, hallucinations, ataxia, loss of coordination, 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.

    Pharmacology

    Clemastine is an antihistamine with anticholinergic 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:

    • Increased capillary permeability
    • Increased capillary dilatation
    • Edema (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 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 does also act as FIASMA (functional inhibitor of acid sphingomyelinase).[2]

    Clemastine is rapidly absorbed from the gastrointestinal tract and peak plasma concentrations are attained in 2–4 hours. Antihistamines are thought to be metabolized in the liver, mostly by mono-/didemethylation and glucuronide conjugation. It is an inhibitor of cytochrome P450 CYP2D6 and may interfere with other drugs metabolized by this isozyme.

    Mechanism of action

    Clemastine is a selective histamine H1 antagonist. It binds to the histamine H1 receptor, thus blocking the action of endogenous histamine, which leads to temporary relief of the negative symptoms caused by histamine.

    Society and culture

    Clemastine is an OTC drug, and is available under many names and dosage forms worldwide. Most common brand name is Tavegyl.[3]

    References

    1. ↑ Anon., GB 942152 (1963).
    2. ↑ Kornhuber J, Muehlbacher M, Trapp S, Pechmann S, Friedl A, Reichel M, Mühle C, Terfloth L, Groemer T, Spitzer G, Liedl K, Gulbins E, Tripal P (2011). "Identification of novel functional inhibitors of acid sphingomyelinase". PLoS ONE. 6 (8): e23852. doi:10.1371/journal.pone.0023852. PMC 3166082. PMID 21909365.
    3. ↑ drugs.com Clemastine at drugs.com international listings Page accessed May 10, 2015
    This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.