Clemastine

Clemastine
Clinical data
AHFS/Drugs.com Monograph
MedlinePlus a682542
Pregnancy
category
Routes of
administration		 Oral
ATC code D04AA14 (WHO) R06AA04 (WHO)
Legal status
Legal status
  • Unscheduled;
    OTC
Pharmacokinetic data
Bioavailability 39.2%
Metabolism Hepatic
Biological half-life 21.3 hours
Excretion Renal
Identifiers
CAS Number 15686-51-8 YesY
PubChem (CID) 26987
IUPHAR/BPS 6063
DrugBank DB00283 YesY
ChemSpider 25129 YesY
UNII 95QN29S1ID YesY
KEGG D03535 YesY
ChEBI CHEBI:3738 YesY
ChEMBL CHEMBL1626 YesY
Chemical and physical data
Formula C21H26ClNO
Molar mass 343.9 g/mol
3D model (Jmol) Interactive image
  (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:

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 3166082Freely accessible. PMID 21909365.
  3. ↑ drugs.com Clemastine at drugs.com international listings Page accessed May 10, 2015
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