Meclizine

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Meclizine
Systematic (IUPAC) name
(RS)-1-[(4-chlorophenyl)(phenyl)methyl]-4-(3-methylbenzyl)piperazine
Clinical data
MedlinePlusa682548
Pregnancy cat.B (US)
Legal statusPrescription Only (S4) (AU) OTC (CA) OTC (US)
RoutesOral, sublingual/buccal
Pharmacokinetic data
Metabolismhepatic
Half-life6 hours
Identifiers
CAS number569-65-3
ATC codeR06AE05
PubChemCID 4034
IUPHAR ligand2757
DrugBankDB00737
ChemSpider3894 YesY
UNII3L5TQ84570 YesY
ChEMBLCHEMBL1623
Chemical data
FormulaC25H27ClN2 
Mol. mass390.948 g/mol
Physical data
Boiling point230 °C (446 °F)
 YesY (what is this?)  (verify)
 
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Meclizine
Systematic (IUPAC) name
(RS)-1-[(4-chlorophenyl)(phenyl)methyl]-4-(3-methylbenzyl)piperazine
Clinical data
MedlinePlusa682548
Pregnancy cat.B (US)
Legal statusPrescription Only (S4) (AU) OTC (CA) OTC (US)
RoutesOral, sublingual/buccal
Pharmacokinetic data
Metabolismhepatic
Half-life6 hours
Identifiers
CAS number569-65-3
ATC codeR06AE05
PubChemCID 4034
IUPHAR ligand2757
DrugBankDB00737
ChemSpider3894 YesY
UNII3L5TQ84570 YesY
ChEMBLCHEMBL1623
Chemical data
FormulaC25H27ClN2 
Mol. mass390.948 g/mol
Physical data
Boiling point230 °C (446 °F)
 YesY (what is this?)  (verify)

Meclizine (INN,[1] or meclozine) is an antihistamine considered to be an antiemetic. It is sold under the brand names Bonine, Bonamine, Antivert, Postafen, Sea Legs, and Dramamine (Less Drowsy Formulation). Emesafene is a combination of meclizine (1/3) and pyridoxine (2/3). In Canada, Antivert Tab (which is no longer available) was a combination of meclizine and nicotinic acid.[2]

Classification[edit]

Meclizine is a first-generation antihistamine of the piperazine class. It is structurally and pharmacologically similar to buclizine, cyclizine, and hydroxyzine, but has a shorter half-life of six hours compared to cyclizine and hydroxyzine with about 20 hours (though half-life should not be confused with frequency of duration). It is used as an antivertigo/antiemetic agent, specifically in the prevention and treatment of nausea, vomiting, and dizziness associated with motion sickness.[3]

Meclizine is less anticholinergic than many other antihistamines and other agents used for their antiemetic and antipruritic effects.[citation needed] Along with the aforementioned efficacy against nausea and itching, meclizine also shares the anxiolytic, analgesic-sparing (potentiating), sedative, and other effects of its chemical relatives cyclizine and hydroxyzine to varying extents.[citation needed] Related to this is the reported ability of meclizine to potentiate the antispasmodic, antidiarrhoeal, and other effects of diphenoxylate, loperamide, and difenoxin.[citation needed] Meclizine is sometimes combined with opioids, especially ones of the open-chain class like methadone, dextropropoxyphene, and dipipanone (originally combined with meclizine's parent drug cyclizine, the brand name of this combination is Diconal). The trend of mixing piperazine antihistamines has caught on in the United States[citation needed], with some methadone users potentiating their doses with meclizine or hydroxyzine (cyclizine has only just recently been introduced to the U.S. OTC market in 2009, sold under the brand name Marezine at higher prices than generic equivalents of meclizine and hydroxyzine).

Mechanism of action[edit]

Meclizine is an antagonist at H1 receptors. It possesses anticholinergic, central nervous system depressant, and local anesthetic effects. Its antiemetic and antivertigo effects are not fully understood, but its central anticholinergic properties are partially responsible. The drug depresses labyrinth excitability and vestibular stimulation, and it may affect the medullary chemoreceptor trigger zone.[3]

Uses[edit]

Meclizine is approved by the U.S. Food and Drug Administration (FDA) to treat symptoms of motion sickness and for management of vertigo that stems from diseases affecting the vestibular system. Meclizine's safety and efficacy in children younger than 12 years old has not been established, therefore use in this population is not recommended. Also, meclizine should be taken with caution in the elderly (older than 65 years) because of increased risk of confusion and amnesia.[4]

Motion sickness[edit]

Meclizine is effective in inhibiting the symptoms of motion sickness, such as nausea, vomiting, and dizziness. The recommended dose is 25–50 mg orally, taken one hour before travel. The dose may be repeated every 24 hours as needed.[3]

The drug is also safe for treating nausea in pregnancy[5] and is a first-line therapy for this use.[6][7] Doxylamine is similarly safe.

Vertigo[edit]

Meclizine may be effective in relieving vertigo experienced as a result of inner ear infections or other conditions. The recommended dose is 25–100 mg per day orally, in divided doses.[3]

Side effects[edit]

Some common side effects such as drowsiness, dry mouth, and tiredness may occur. Meclizine has been shown to have fewer dry mouth side effects than the traditional treatment for motion sickness, transdermal scopolamine.[8] A very serious allergic reaction to this drug is unlikely, but seek immediate medical attention if it occurs. Symptoms of a serious allergic reaction may include: rash, itching/swelling, severe dizziness, and/or trouble breathing.[9]

Drowsiness[edit]

Drowsiness may result as a side effect of taking meclizine. Users are advised not to operate heavy machinery while under the influence. The consumption of alcohol while under the influence of meclizine may result in additional drowsiness.

Special considerations in the elderly[edit]

As with any anticholinergic agent, meclizine may cause confusion or aggravate symptoms in those with dementia in the geriatric population (older than 65 years). Therefore caution should be used when administering meclizine to the elderly.[10]

Synthesis[edit]

(4-Chlorphenyl)-phenylmethanol is halogenated with thionyl chloride before adding acetylpiperazine. The acetyl group is cleaved with diluted sulfuric acid. An N-alkylation of the piperzine ring with 3-methylbenzylchloride completes the synthesis.[11]

Meclozine synthesis 01.svg

Alternatively, the last step can be replaced by a reductive N-alkylation with 3-methylbenzaldehyde. The reductive agent is hydrogen, and Raney nickel is used as a catalyst.[12][13]

Meclozine synthesis 02.svg

Meclizine is obtained and used as a racemate, a 1:1 mixture of the two stereoisomers. Drug forms contain the dihydrochloride.

References[edit]

  1. ^ Guidelines on the Use of INNs for Pharmaceutical Substances (1997). Accessed November, 2013 "Guidance on INN." WHO.
  2. ^ DrugBank. Drugbank: Drug card for Meclizine David Wishard: University of Alberta, Canada. Accessed November 7, 2010.
  3. ^ a b c d Clinical Pharmacology. Clinical Pharmacology, revised November 20, 2009, accessed November 7, 2010.[broken citation]
  4. ^ MICROMEDEX 2.0. Accessed November 7, 2010.[broken citation]
  5. ^ Källén B, Mottet I (2003). "Delivery outcome after the use of meclizine in early pregnancy". European Journal of Epidemiology 18 (7): 665–669. PMID 12952140. Retrieved 2010-09-17. 
  6. ^ "Antiemetische Therapie bei Schwangerschaftserbrechen" [Antiemetic therapy in pregnancy]. Arznei-Telegramm (in German) 40: 87–89. 2009. 
  7. ^ Embryotox: Meclozin (German)
  8. ^ Dahl E, Offer-Ohlsen D, Lillevold PE, Sandvik L. Transdermal scopolamine, oral meclizine, and placebo in motion sickness. Clinical Pharmacology And Therapeutics [Clin Pharmacol Ther] 1984 Jul; Vol. 36 (1), pp. 116-20. Available from: MEDLINE: Ipswich, MA. PMID 6734040
  9. ^ Meclizine - oral, Antivert, D-vert, Dramamine II. Accessed November 7, 2010.
  10. ^ Merck Manuals, Online Medical Library: Meclizine (Drug Information Provided by Lexi-Comp), revised January 2010, accessed November 7, 2010.
  11. ^ J.-H. Fuhrkop, G. Li (2003). Organic Synthesis. Concepts and Methods. Wiley. p. 237. ISBN 978-3-527-30272-7. 
  12. ^ US 2 709 169 (UCB, 1955)
  13. ^ A. Kleemann, J. Engel, B. Kutscher, D. Reichert (2001). Pharmaceutical Substances. Synthesis, Patents, Applications (4 ed.). Thieme. ISBN 3-13-115134-X. 

External links[edit]