MSD Manual

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Antihistamine Dosages

Antihistamine Dosages

Drug

Dosage

Diphenhydramine

2–4 mg/kg, IM, PO, or SC, q 8–12 h as needed

Hydroxyzine

0.5–2 mg/kg, PO or IV, q 6–8 h as needed

Chlorpheniramine

Cats: 2–4 mg/cat, PO, IM, or SC, q 12 h as needed

Dogs <20 kg: 4 mg, PO, IM, or SC, q 8 h as needed

Dogs >20 kg: 8 mg per dog or 0.25–0.5 mg/kg, PO, IM, or SC, q 8 h as needed

Cyproheptadine

0.25–0.5 mg/kg, PO, q 8 h as needed for appetite stimulation; 1.1 mg/kg, q 12 h as needed for management of dysphoria from serotonin syndrome

Terfenadine

5 mg/kg, PO, q 12 h as needed

Clemastine

Cats: 0.05 mg/kg, PO, q 12 h as needed

Dogs: 0.1 mg/kg, PO or IV, q 12 h as needed

Trimeprazine

1 mg/kg, PO, q 12 h as needed

Cetirizine

Dogs: 1 mg/kg or 10–20 mg per dog, PO, q 12–24 h as needed

Cats: 1 mg/kg or 5 mg/cat, PO, q 12–24 h as needed

Fexofenadine

Dogs: 2–5 mg/kg, PO, q 12–24 h as needed

Cats: 10–15 mg/cat, PO, q 12–24 h as needed