Meclizine
**Meclizine** is a first-generation piperazine antihistamine widely used in veterinary medicine primarily for its antiemetic and anti-motion sickness properties. * **Clinical Utility**: It is particularly effective for managing peripheral vestibular disease, vertigo, and motion sickness in dogs and cats. * **Additional Properties**: Beyond its antihistamine activity, meclizine possesses mild CNS depressant, antispasmodic, and local anesthetic effects. * **Safety Profile**: Generally well-tolerated, though its anticholinergic properties require cautious use in patients with specific comorbidities like glaucoma or urinary retention.
Mechanism: Meclizine acts primarily as an antagonist at central **H1-receptors** and **muscarinic acetylcholine receptors**. * **Vestibular Pathway**: Blocks histaminergic and cholinergic signals originating from the vestibular apparatus โ reduces stimulation of the **Chemoreceptor Trigger Zone (CTZ)** and the vomiting center in the medulla. * **Anticholinergic Activity**: Central muscarinic antagonism contributes significantly to its efficacy against motion sickness and vertigo. * **CNS Depression**: Causes generalized CNS depression, which may aid in its antiemetic and sedative effects.
Dosing by species
- General/Vestibular ยท 12.5 mg per cat ยท PO ยท once daily
- General ยท 6.25 mg/5 kg of body weight ยท PO ยท Not specified
- Anti-emetic ยท 4 mg/kg ยท PO ยท once a day
- Palliative treatment of vertigo ยท 12.5 mg per cat ยท PO ยท once daily
- Rolling, torticollis, motion sickness (Rabbits) ยท 2-12 mg/kg ยท PO ยท once daily
- Adjunctive treatment of torticollis, head tilt ('wry neck') (Rabbits) ยท 12.5 mg (total dose) ยท PO ยท q12-24h
- Supportive treatment of peripheral vestibular disease ยท 25 mg per dog ยท PO ยท once daily ยท Treatment is usually unnecessary after 72-96 hours
- Vestibular suppressant ยท 12.5-50 mg (total dose per dog) ยท PO ยท twice daily
- Anti-emetic ยท 4 mg/kg ยท PO ยท once a day
- Palliative treatment of vertigo ยท 25 mg per dog ยท PO ยท once daily
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Hypersensitivity to meclizine
Adverse effects
- Sedation
- Dry mucous membranes
- Dry eyes
- Tachycardia
- Contradictory CNS stimulation
- Inappetence (especially in cats)
Drug interactions
- CNS Depressants ยท Use with other CNS depressants may cause additive sedation
- Anticholinergic Drugs ยท Other anticholinergic drugs may cause additive anticholinergic effects
Monitoring
- Clinical efficacy (reduction in vomiting, motion sickness, or vestibular signs)
- Adverse effects (sedation, anticholinergic signs)
Overdose
Moderate overdosage may result in drowsiness alternating with hyperexcitability. **Massive overdosages** may result in: * Profound CNS depression * Hallucinations * Seizures * Severe anticholinergic effects (tachycardia, urinary retention, etc.) **Treatment**: * Consider gut emptying when patients present soon after ingestion. * Treatment is symptomatic and supportive. * > **Warning**: Avoid respiratory depressant medications.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturerโs current label.