Adult: Doses are expressed in terms of base (1 mg clemastine base is equivalent to 1.34 mg clemastine fumarate): Usual dose: 1 mg bid, increased up to Max 6 mg daily, if necessary. Child: Doses are expressed in terms of base (1 mg clemastine base is equivalent to 1.34 mg clemastine fumarate): 1-3 years 0.25-0.5 mg bid; 3-6 years 0.5 mg bid; 6-11 years 0.5-1 mg bid; ≥12 years Same as adult dose. Dosage recommendations may vary between countries (refer to specific local guidelines).
Administration
Clemastine May be taken with or without food. May be taken w/ meals to reduce GI discomfort.
Contraindications
Lower respiratory tract symptoms (e.g. asthma). Premature infants, neonates and children <1 year. Lactation. Concomitant use with MAOIs. Contraindications may vary between individual products (refer to specific product labelling for detailed information).
Special Precautions
Patient with CV disease (including hypertension and ischaemic heart disease), thyroid dysfunction, increased IOP or angle-closure glaucoma, prostatic hyperplasia, bladder neck obstruction and/or genitourinary obstruction, pyloroduodenal obstruction including stenotic peptic ulcer, history of asthma. Children and elderly. Pregnancy.
Adverse Reactions
Significant: CNS depression (e.g. drowsiness, dizziness, sedation). Cardiac disorders: Tachycardia, palpitations. Gastrointestinal disorders: Dry mouth, nausea, constipation. General disorders and administration site conditions: Fatigue. Nervous system disorders: Headache. Skin and subcutaneous tissue disorders: Rash.
This drug may impair physical or mental abilities, if affected, do not drive or operate machinery.
Overdosage
Symptoms: CNS depression to stimulation; depressed level of consciousness, excitability, hallucinations, convulsions; dry mouth, mydriasis, flushing, gastrointestinal reactions, tachycardia. Management: Symptomatic treatment. Induce vomiting by giving a glass of water or milk. If vomiting is unsuccessful, gastric lavage with isotonic and 1/2 isotonic saline may be performed within 3 hours after ingestion. Vasopressors may be given in case of hypotension.
Drug Interactions
May potentiate the sedative effects of CNS depressants (e.g. antidepressants, anxiolytics, opioid analgesics, hypnotics). May enhance the effect of some anticholinergic drugs (e.g. atropine, TCAs). Potentially Fatal: Prolonged and intensified anticholinergic effects with MAOIs.
Food Interaction
May increase the CNS depressant effects of alcohol.
Action
Description: Mechanism of Action: Clemastine, a monoethanolamine derivative, is a 1st-generation sedating antihistamine. It competes with histamine for H1-receptor sites on effector cells in the blood vessels, uterus, gastrointestinal tract, and respiratory tract. It also suppresses oedema formation, flare, and pruritus caused by histaminic activity. Additionally, it also exhibits anticholinergic and sedative effects. Onset: 2 hours. Peak effect: 5-7 hours. Duration: 10-12 hours; may persist for up to 24 hours. Pharmacokinetics: Absorption: Rapidly and almost completely absorbed from the gastrointestinal tract. Bioavailability: Approx 40%. Time to peak plasma concentration: 2-4 hours. Distribution: Enters breast milk (small amounts). Volume of distribution: Approx 800 L. Metabolism: Metabolised in the liver. Excretion: Via urine (approx 42% as metabolites). Elimination half-life: Approx 21 hours (range: 10-33 hours).
Chemical Structure
Clemastine Source: National Center for Biotechnology Information. PubChem Compound Summary for CID 26987, Clemastine. https://pubchem.ncbi.nlm.nih.gov/compound/Clemastine. Accessed July 28, 2025.
R06AA04 - clemastine ; Belongs to the class of aminoalkyl ethers used as systemic antihistamines.
References
Brayfield A, Cadart C (eds). Clemastine Fumarate. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 01/07/2025.Clemastine Fumarate Syrup (Genus Lifesciences). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed. Accessed 01/07/2025.Clemastine Fumarate Tablet (Genus Lifesciences). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed. Accessed 01/07/2025.Clemastine Fumarate. UpToDate Lexidrug, AHFS DI (Adult and Pediatric) Online. American Society of Health-System Pharmacists, Inc. Waltham, MA. UpToDate, Inc. https://online.lexi.com. Accessed 01/07/2025.Clemastine. Gold Standard Drug Database in ClinicalKey [online]. Elsevier Inc. https://www.clinicalkey.com. Accessed 01/07/2025.Clemastine. UpToDate Lexidrug, Lexi-Drugs Multinational Online. Waltham, MA. UpToDate, Inc. https://online.lexi.com. Accessed 01/07/2025.Tavegil Tablets (Thornton & Ross Ltd.). MHRA. https://products.mhra.gov.uk. Accessed 01/07/2025.
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