Vetdrugs 2.0Clemastine is a first-generation H1 antihistamine used empirically for symptomatic relief of allergic disease in veterinary patients. It has been used particularly for pruritic skin conditions in dogs and cats. Oral bioavailability is low in dogs and horses, and reported clinical benefit for allergic pruritus has been inconsistent.
Group
First-generation H1 antihistamine
Mechanism of Action
Clemastine inhibits histamine H1-receptor signaling in peripheral tissues. This can reduce histamine-mediated capillary permeability, swelling and sensory-nerve stimulation associated with itching. It antagonizes the effects of released histamine rather than preventing mediator release. Additional muscarinic-receptor blockade and central histamine-receptor activity contribute to its pharmacologic effects.
Dose Rates
Dogs
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Allergic pruritus | 0.05–0.1 mg/kg | PO | Every 12 h | |
| Higher-dose allergic pruritus treatment | 0.5–1.5 mg/kg | PO | Every 12 h | Separate high-dose alternative; low oral efficacy remains a limitation. |
Horses
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Allergic signs | 50 mcg/kg | IV | Every 8 h | Oral administration is poorly absorbed and not a substitute. |
Cats
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Allergic signs | 0.34–0.68 mg/animal | PO | Every 12 h | Confirm whether the prescribed amount is clemastine base or fumarate; the older dose source does not state the basis. |
| Atopy | 0.15 mg/kg | PO | Every 12 h | Older regimen with undefined base-versus-fumarate basis; do not automatically match salt-labelled tablets. |
Indications
- Empirical adjunctive relief of histamine-associated allergic pruritus in dogs and cats; clinical effectiveness is variable and incompletely established.
- Symptomatic management of selected histamine-mediated cutaneous allergic reactions, including urticaria, in veterinary patients.
Contraindications
- Assess antimuscarinic and sedation risks for the individual patient.
- Use cautiously with urinary outflow obstruction, prostatic enlargement, angle-closure glaucoma, severe cardiac failure or pyloroduodenal obstruction.
Interactions
- No veterinary interactions are identified in the supplied material.
Adverse effects
- Sedation
- Dry mouth and reduced gastrointestinal secretion
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Clemastine 1.34 mg tablet | Tablet | 1.34 mg / tablet | PO |
| Clemastine fumarate syrup 0.1 mg/mL The described Tavist syrup contains 5.5% alcohol. | Oral Liquid | 0.1 mg / mL | PO |
| Clemastine fumarate 2.68 mg tablet | Tablet | 2.68 mg / tablet | PO |
Monitoring and Administration
Oral absorption in dogs and horses is very low; high oral doses have not reliably suppressed skin reactions.
The source includes 1.34 mg tablet alternatives: half a tablet below 10 kg, one tablet at 10–25 kg, and 1.5 tablets above 25 kg, every 12 hours. These are empirical alternatives, not verified label weight bands.
The described Tavist syrup contains 5.5% alcohol.
The source also lists a 2.64 mg prescription tablet; this strength is not added because the intended fumarate-versus-base presentation is unclear.
Official tablet information establishes 1.34 mg and 2.68 mg clemastine fumarate strengths; the earlier 2.64 mg figure is corrected. Fumarate and clemastine-base amounts are not interchangeable.