Meclizine
Meclizine is a first-generation H1 antihistamine with central antimuscarinic properties. It is used extensively in human vestibular disorders and has an empirical veterinary role in motion-associated vomiting, principally in dogs. Veterinary clinical efficacy is poorly characterized, and its proposed antiemetic activity depends on effects within vestibular and brainstem pathways.
Group
Antihistamine antiemetic
Mechanism of Action
Meclizine inhibits histamine H1 signaling and has central antimuscarinic effects. These actions can reduce transmission from vestibular pathways to the brainstem networks coordinating nausea and vomiting. The resulting effect is most relevant to motion-related or vestibular stimuli. Its complete antiemetic mechanism and the importance of individual receptor effects in dogs remain incompletely defined.
Dose Rates
Dogs
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Motion sickness | 25 mg/animal | PO | Every 24 h | Give 1 hour before travel; clinical efficacy is uncertain. |
| Vestibular disease or vertigo | 25 mg/animal | PO | Every 24 h | Up to 4 days; Supportive treatment often unnecessary after 72-96 hours. |
| Vestibular suppression | 12.5–50 mg/animal | PO | Every 12 h | |
| Historical antiemetic alternative | 4 mg/kg | PO | Every 24 h | Antihistamine antiemetic efficacy is poorly established, especially in cats. |
Cats
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Historical motion sickness regimen | 12.5 mg/animal | PO | Every 24 h | Historical dose only; antihistamines are not effective antiemetics in cats and another agent is recommended. |
| Historical antiemetic alternative | 4 mg/kg | PO | Every 24 h | Antihistamine antiemetic efficacy is poorly established, especially in cats. |
| Vertigo | 12.5 mg/animal | PO | Every 24 h |
Rabbits
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Torticollis or rolling adjunct | 2–12 mg/kg | PO | Every 24 h | |
| Torticollis or head-tilt adjunct | 12.5 mg/animal | PO | Every 12–24 h |
Indications
- Empirical prevention or treatment of motion-associated vomiting in dogs, with limited controlled clinical evidence.
- Empirical symptomatic management of selected vestibular-associated nausea in dogs; clinical benefit is unestablished.
Contraindications
- Use cautiously with gastrointestinal obstruction or glaucoma.
Interactions
- Other sedating or anticholinergic drugs may increase effects.
Adverse effects
- Sedation and antimuscarinic effects
Toxicity
Assess central depression and anticholinergic signs after excess exposure.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Meclizine 12.5 mg tablet | Tablet | 12.5 mg / tablet | PO |
| Meclizine 25 mg tablet | Tablet | 25 mg / tablet | PO |
| Meclizine 50 mg tablet | Tablet | 50 mg / tablet | PO |
Monitoring and Administration
Consider administration 1 hour before travel; agents with demonstrated veterinary efficacy may be preferred.