Clemastine

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Clemastine
Clemastine.svg
Clemastine ball-and-stick.png
Names
Trade namesTavegil, Dayhist, Tavist, others
Other namesClemastine fumarate, meclastin, mecloprodin
  • (2R)-2-{2-[(1R)-1-(4-chlorophenyl)-1-phenylethoxy]ethyl}-1-methylpyrrolidine
Clinical data
Drug class1st-generation antihistamine[1]
Main usesHay fever, hives[2]
Side effectsSleepiness, dizziness, poor coordination, upset stomach[1]
Pregnancy
category
  • US: B (No risk in non-human studies)
Routes of
use
By mouth
External links
AHFS/Drugs.comMonograph
US NLMClemastine
MedlinePlusa682542
Legal
Legal status
Pharmacokinetics
Bioavailability39.2%
MetabolismLiver
Elimination half-life21.3 hours
ExcretionKidney
Chemical and physical data
FormulaC21H26ClNO
Molar mass343.90 g·mol−1
3D model (JSmol)
  • Clc1ccc(cc1)[C@](OCC[C@@H]2N(C)CCC2)(c3ccccc3)C
  • InChI=1S/C21H26ClNO/c1-21(17-7-4-3-5-8-17,18-10-12-19(22)13-11-18)24-16-14-20-9-6-15-23(20)2/h3-5,7-8,10-13,20H,6,9,14-16H2,1-2H3/t20-,21-/m1/s1 checkY
  • Key:YNNUSGIPVFPVBX-NHCUHLMSSA-N checkY

Clemastine, also known as meclastin, is a medication used to treat allergies such as hay fever and hives.[2][3] It may also be used for symptoms of the common cold.[1] It is taken by mouth.[2]

Common side effects include sleepiness, dizziness, poor coordination, and an upset stomach.[1] Other side effects may include agitation, dry mouth, and constipation.[2] There is no evidence of harm with use in pregnancy, but such use has not been well studied.[4] It should not be used when breastfeeding.[1] It is a first-generation antihistamine.[1]

Patented in 1960, it came into medical use in 1967.[5] It is available as a generic medication and over the counter.[1] In the United Kingdom 60 pills of 1 mg costs the NHS about £7 as of 2021.[2] This amount in the United States costs about 18 USD.[6]

Medical uses

Clemastine is used to relieve hay fever and allergy symptoms, including sneezing; runny nose; and red, itchy, tearing eyes. Prescription strength clemastine is also used to relieve the itching and swelling of hives.[7]

Dosage

It is taken at a dose of 1 to 3 mg twice per day.[2]

A dose of 1.34 mg of clemastine fumarate is equal to 1 mg clemastine.[1]

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.[medical citation needed]

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).[8]

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.[medical citation needed]

Society and culture

Clemastine is an OTC drug, and is available under many names and dosage forms worldwide. Brand names include Tavegyl.[9]

References

  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 "Clemastine Monograph for Professionals". Drugs.com. Archived from the original on 12 June 2021. Retrieved 5 January 2022.
  2. 2.0 2.1 2.2 2.3 2.4 2.5 BNF 81: March-September 2021. BMJ Group and the Pharmaceutical Press. 2021. p. 300. ISBN 978-0857114105.
  3. "Clemastine [USAN:INN:BAN]". Archived from the original on 2 May 2021. Retrieved 5 January 2022.
  4. "Clemastine Use During Pregnancy". Drugs.com. Archived from the original on 3 December 2020. Retrieved 5 January 2022.
  5. Fischer, Jnos; Ganellin, C. Robin (2006). Analogue-based Drug Discovery. John Wiley & Sons. p. 547. ISBN 9783527607495. Archived from the original on 2021-08-29. Retrieved 2021-08-25.
  6. "Clemastine Prices, Coupons & Savings Tips - GoodRx". GoodRx. Retrieved 5 January 2022.
  7. "Clemastine". MedlinePlus. Archived from the original on 2021-06-12. Retrieved 2021-08-25.
  8. 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.
  9. drugs.com Clemastine at drugs.com international listings Archived 2020-07-28 at the Wayback Machine Page accessed May 10, 2015

External links

Identifiers: