Introduction
Meclizine is an antihistamine medication primarily used for the management of nausea, vomiting, and dizziness associated with motion sickness and vertigo. First approved by the FDA in the 1950s, this piperazine-class antihistamine has remained a cornerstone therapy for vestibular disorders due to its favorable safety profile and efficacy.
Mechanism of Action
Meclizine exerts its therapeutic effects through central anticholinergic and antihistaminic (H1 receptor blockade) actions. It inhibits stimulation of the labyrinthine apparatus and the chemoreceptor trigger zone (CTZ) in the medulla oblongata. The drug also demonstrates mild sedative properties through its action on central histamine receptors, contributing to its anti-vertigo effects.
Indications
- FDA-approved indications:
- Management of nausea and vomiting associated with motion sickness - Management of vertigo associated with diseases affecting the vestibular system
- Off-label uses:
- Management of nausea and vomiting in pregnancy (limited data) - Adjunctive therapy in vestibular migraine - Symptomatic relief in Meniere's disease
Dosage and Administration
Adults:- Motion sickness: 25-50 mg orally 1 hour before travel; may repeat every 24 hours as needed
- Vertigo: 25-100 mg daily in divided doses
Pharmacokinetics
- Absorption: Well absorbed from gastrointestinal tract
- Distribution: Widely distributed throughout body tissues; crosses blood-brain barrier
- Protein binding: Extensive (unknown exact percentage)
- Metabolism: Hepatic via cytochrome P450 enzymes
- Elimination: Primarily renal excretion; elimination half-life approximately 6 hours
- Onset of action: Approximately 1 hour after oral administration
- Duration of effect: 8-24 hours
Contraindications
- Hypersensitivity to meclizine or any component of the formulation
- Concomitant use with monoamine oxidase inhibitors (MAOIs)
- Narrow-angle glaucoma
- Severe urinary retention
- Neonates and infants (due to potential for anticholinergic effects)
Warnings and Precautions
- CNS depression: May impair mental and/or physical abilities; caution when operating machinery
- Anticholinergic effects: Use with caution in patients with:
- Prostatic hypertrophy - Gastrointestinal obstruction - Cardiovascular disease - Hyperthyroidism
- Pregnancy: Category B - use only if clearly needed
- Lactation: Excreted in breast milk; use with caution
- Elderly patients: Increased risk of sedation, confusion, and anticholinergic effects
- Phenylketonuria: Some formulations may contain phenylalanine
Drug Interactions
- CNS depressants: Enhanced sedative effects (alcohol, benzodiazepines, opioids)
- Anticholinergic agents: Additive effects (tricyclic antidepressants, antipsychotics)
- MAO inhibitors: Risk of hypertensive crisis (contraindicated)
- Potassium supplements: Increased risk of esophageal irritation (with solid oral dosage forms)
Adverse Effects
Common (>10%):- Drowsiness/sedation
- Dry mouth
- Headache
- Fatigue
- Blurred vision
- Constipation
- Nervousness
- Gastrointestinal upset
- Tachycardia
- Urinary retention
- Allergic reactions
- Paradoxical excitation (especially in children)
Monitoring Parameters
- Efficacy assessment: Reduction in nausea/vomiting/vertigo symptoms
- Adverse effects: Sedation, anticholinergic effects
- Mental status changes (especially in elderly)
- Visual acuity (if blurred vision reported)
- Urinary function in predisposed patients
Patient Education
- Take as directed; do not exceed recommended dosage
- Avoid alcohol and other CNS depressants during therapy
- Be cautious when driving or operating machinery until response is known
- Chewable tablets may contain phenylalanine (important for PKU patients)
- Report persistent drowsiness, confusion, or vision changes
- For motion sickness: Take 1 hour before travel
- Store at room temperature away from moisture
References
1. FDA Prescribing Information: Meclizine Hydrochloride Tablets 2. Lexicomp Online: Meclizine Monograph 3. Micromedex Solutions: Meclizine Drug Information 4. Brunton LL, Hilal-Dandan R, Knollmann BC. Goodman & Gilman's: The Pharmacological Basis of Therapeutics. 13th ed. 5. Hain TC, Yacovino D. Pharmacologic treatment of persons with dizziness. Neurol Clin. 2005;23(3):831-853. 6. Weiser M. Motion sickness. In: UpToDate. Post TW (Ed). Updated 2022. 7. Takeda N, Morita M, Hasegawa S, et al. Neuropharmacology of motion sickness and emesis. Acta Otolaryngol Suppl. 1993;501:10-15.