Meclizine

Meclizine, sold under the brand names Bonamine among others, is an antihistamine used to treat motion sickness and the feeling like the world is spinning (vertigo).[1] It is taken by mouth.[1] Effects generally begin in an hour and last for up to a day.[1]

Meclizine
Clinical data
Trade namesBonamine, Antivert, others
Other namesMeclozine
AHFS/Drugs.comMonograph
MedlinePlusa682548
Pregnancy
category
  • US: B (No risk in non-human studies)
    Routes of
    administration    		By mouth, under the tongue, in the cheek
    ATC code
    Legal status
    Legal status
    • AU: S4 (Prescription only)
    • CA: OTC
    • US: OTC
    Pharmacokinetic data
    MetabolismLiver
    Elimination half-life6 hours
    Identifiers
    CAS Number
    PubChem CID
    IUPHAR/BPS
    DrugBank
    ChemSpider
    UNII
    ChEMBL
    CompTox Dashboard (EPA)
    ECHA InfoCard100.008.477
    Chemical and physical data
    FormulaC25H27ClN2
    Molar mass390.948 g/mol g·mol−1
    3D model (JSmol)
    Boiling point230 °C (446 °F)
     NY (what is this?)  (verify)

    Common side effects include sleepiness and dry mouth.[1] Serious side effects may include allergic reactions.[1] Use in pregnancy appears safe but has not been well studied while use in breastfeeding is of unclear safety.[2] It is believed to work in part by anticholinergic and antihistamine mechanisms.[1]

    Meclizine was patented in 1951 and came into medical use in 1953.[3] It is available as a generic medication and often over the counter.[1][4] In the United States the wholesale cost per dose is about US$0.03.[5] It is not available in Australia.[6] In 2016 it was the 162nd most prescribed medication in the United States with more than three million prescriptions.[7]

    Medical uses

    Meclizine is used to treat symptoms of motion sickness. Safety and efficacy in children younger than twelve years of age has not been established; therefore, use in this population is not recommended. Meclizine should be taken with caution in the elderly due to increased risk of confusion and amnesia.[8]

    Motion sickness

    Meclizine is effective in inhibiting the symptoms of motion sickness, such as nausea, vomiting, and dizziness.[9]

    The drug is safe for treating nausea in pregnancy[10] and is a first-line therapy for this use.[11][12] Doxylamine is similarly safe. Meclizine may not be strong enough for especially sickening motion stimuli and second-line defenses should be tried in those cases.[13]

    Vertigo

    Meclizine is effective in relieving vertigo experienced as a result of inner ear infection or positional or chronic vertigo.[14]

    Side effects

    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.[15] A very serious allergic reaction to this drug is unlikely, but immediate medical attention should be sought if it occurs. Symptoms of a serious allergic reaction may include rash, itching, swelling, severe dizziness, and trouble breathing.[16]

    Drowsiness

    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.

    Elderly

    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.[17]

    Mechanism of action

    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.[18] Meclizine also is a dopamine antagonist at D1-like and D2-like receptors but does not cause catalepsy[note 1] in mice, perhaps because of its anticholinergic activity.[19]

    Chemistry

    Meclizine is a first-generation antihistamine (nonselective H1 antagonist) 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 duration). It is used as an antivertigo/antiemetic agent, specifically in the prevention and treatment of nausea, vomiting, and dizziness associated with motion sickness.[18] Meclizine is sometimes combined with opioids, especially ones of the open-chain class like methadone, dextropropoxyphene, and dipipanone. Similarly, Diconal is a combination drug containing dipipanone and cyclizine.

    Synthesis

    (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 piperazine ring with 3-methylbenzylchloride completes the synthesis.[20]

    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.[21][22]

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

    Names

    Meclizine is an international nonproprietary name.[23]

    It is sold under the brand names Bonine, Bonamine, Antivert, Postafen, Sea Legs, and Dramamine II (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.[24]

    Notes
    1. "[C]atalepsy was assessed by the bar method[:] the front paws were gently placed on a horizontal metal bar with 2 mm diameter suspended 4 cm above, and the length of time the mouse maintains this abnormal posture was measured."[19]

    References
    1. "Meclizine Hydrochloride Monograph for Professionals". Drugs.com. American Society of Health-System Pharmacists. Retrieved 22 March 2019.
    2. "Meclizine Use During Pregnancy". Drugs.com. Retrieved 3 March 2019.
    3. Fischer J, Ganellin CR (2006). Analogue-based Drug Discovery. John Wiley & Sons. p. 547. ISBN 9783527607495.
    4. Cappa M, Cianfarani S, Ghizzoni L, Loche S, Maghnie M (2015). Advanced Therapies in Pediatric Endocrinology and Diabetology: Workshop, Rome, October 2014. Karger Medical and Scientific Publishers. p. 101. ISBN 9783318056372.
    5. "NADAC as of 2019-02-27". Centers for Medicare and Medicaid Services. Retrieved 3 March 2019.
    6. McKenzie G, Broyles B, Evans ME, Page R, Pleunik S, Reiss BS (2016). Pharmacology in Nursing: Australian and New Zealand Edition with Student Resource Access 12 Months. Cengage AU. p. 569. ISBN 9780170362030.
    7. "The Top 300 of 2019". clincalc.com. Retrieved 22 December 2018.
    8. MICROMEDEX 2.0. Accessed November 7, 2010.
    9. "Drugs & Medications". www.webmd.com. Retrieved 2018-12-28.
    10. Källén B, Mottet I (2003). "Delivery outcome after the use of meclozine in early pregnancy" (PDF). European Journal of Epidemiology. 18 (7): 665–9. doi:10.1023/a:1024891618953. PMID 12952140.
    11. "Antiemetische Therapie bei Schwangerschaftserbrechen" [Antiemetic therapy in pregnancy]. Arznei-Telegramm (in German). 40: 87–89. 2009.
    12. Embryotox: Meclozin (in German)
    13. Lawson BD, McGee HA, Castaneda MA, Golding JF, Kass SJ, McGrath CM (2 December 2009). "Evaluation of several common antimotion sickness medications and recommendations concerning their potential usefulness during special operations". Pensacola, Florida: Naval Aerospace Research Lab.
    14. Cohen B, DeJong JM (August 1972). "Meclizine and placebo in treating vertigo of vestibular origin. Relative efficacy in a double-blind study". Archives of Neurology. 27 (2): 129–35. doi:10.1001/archneur.1972.00490140033006. PMID 4339240.
    15. Dahl E, Offer-Ohlsen D, Lillevold PE, Sandvik L (July 1984). "Transdermal scopolamine, oral meclizine, and placebo in motion sickness". Clinical Pharmacology and Therapeutics. 36 (1): 116–20. doi:10.1038/clpt.1984.148. PMID 6734040.
    16. Meclizine - oral, Antivert, D-vert, Dramamine II. Accessed November 7, 2010.
    17. Merck Manuals, Online Medical Library: Meclizine (Drug Information Provided by Lexi-Comp), revised January 2010, accessed November 7, 2010.
    18. Clinical Pharmacology. Clinical Pharmacology, revised November 20, 2009, accessed November 7, 2010.
    19. Haraguchi K, Ito K, Kotaki H, Sawada Y, Iga T (June 1997). "Prediction of drug-induced catalepsy based on dopamine D1, D2, and muscarinic acetylcholine receptor occupancies". Drug Metabolism and Disposition. 25 (6): 675–84. PMID 9193868.
    20. Fuhrkop JH, Li G (2003). Organic Synthesis. Concepts and Methods. Wiley. p. 237. ISBN 978-3-527-30272-7.
    21. US 2 709 169 (UCB, 1955)
    22. Kleemann A, Engel J, Kutscher B, Reichert D (2001). Pharmaceutical Substances. Synthesis, Patents, Applications (4th ed.). Thieme. ISBN 3-13-115134-X.
    23. Guidelines on the Use of INNs for Pharmaceutical Substances (1997). Accessed November, 2013 "Guidance on INN." WHO.
    24. DrugBank. Drugbank: Drug card for Meclizine David Wishard: University of Alberta, Canada. Accessed November 7, 2010.
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