Table: Antihistamine Dosages - Merck Veterinary Manual

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Antihistamine Dosages

Drug	Dosage
Diphenhydramine	2–4 mg/kg, bid-tid
Hydroxyzine	0.5–2 mg/kg, tid-qid
Clorpheniramine	Cats: 2–4 mg, bid
	Dogs <20 kg: 4 mg, tid
	Dogs >20 kg: 8 mg, tid; 0.25–0.5 mg/kg, tid
Cyproheptadine	0.25–0.5 mg/kg, tid; 1.1 mg/kg, bid
Terfenadine	5 mg/kg, bid
Clemastine	Cats: 0.05 mg/kg, bid
	Dogs: 0.1 mg/kg, bid
Trimeprazine	1 mg/kg, bid
Cetirizine	Dogs: 1 mg/kg or 10–20 mg per dog, once or twice daily
	Cats: 1 mg/kg or 5 mg per cat, once or twice daily
Fexofenadine	Dogs: 2–5 mg/kg, once or twice daily
	Cats: 10–15 mg per cat, once or twice daily