Hydroxyzine: veterinary dose and monograph

At a glance

Drug class

Veterinary drug

Also known as

Atarax, Hydroxyzine HCl/pamoate, Hyzine

Species with doses

Dogs, Cats, Horses, Birds and Ferrets

General dose range

2 mg/kg PO q8h — check the species tables for the indication

Routes

PO

Last reviewed

1 October 2026

Indications

• Allergic pruritus — atopic dermatitis, urticaria, insect-bite reactions
• Mild sedation / anxiolysis
• Adjunct antihistamine in allergic/anaphylactoid management
• Pre-treatment to reduce histamine-related reactions

Hydroxyzine dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

Dogs

• Allergic pruritus / mild sedation: Papich 5e: 2 mg/kg q8–12h IM or PO. Plumb’s p.629: 2.2 mg/kg PO three times daily (Gershwin; Paradis; White); flea allergy 2 mg/kg q8h. Response is individual — trial 1–2 weeks.

Cats

• Allergic pruritus: Plumb’s p.629: 1–2 mg/kg or 5–10 mg per cat PO q8–12h (Messinger; Hnilica); recurrent idiopathic LUTD 5–10 mg per cat q12h (Lane). Papich 5e: effective doses not established in cats — cetirizine is an alternative.

Horses

• Allergic dermatitis / urticaria: Plumb's p.630 (Robinson 1992): 0.5–1 mg/kg IM or PO twice daily; pamoate salt 0.67 mg/kg PO q12h. ARCI Class 2 — observe competition withdrawal.

Birds

• Pruritus / feather picking: Plumb’s p.629: 2 mg/kg PO q8h or 1.5–2 mg per 4 oz of drinking water daily (Hillyer 1994); 2 mg/kg PO q12h (Siebert 2003). Adjust to limit drowsiness.

Ferrets

• Allergic pruritus: Plumb's p.630 (Williams 2000): 2 mg/kg PO three times daily.

Contraindications

Glaucoma, urinary retention, GI obstruction (anticholinergic). Significant cardiac disease (QT effects at high dose). Pregnancy (early — teratogenic in some studies). Concurrent CNS depressants (additive sedation). Known hypersensitivity.

Adverse effects

• Sedation, lethargy
• Anticholinergic effects (dry mouth, urinary retention, constipation)
• Occasional paradoxical excitement
• GI upset

Drug interactions

• CNS depressants (sedatives, opioids, anaesthetics): additive sedation
• Anticholinergics: additive (urinary retention, ileus)
• QT-prolonging drugs: caution at high doses
• May suppress allergy skin-test reactions — withdraw before intradermal testing

Pregnancy and lactation

Avoid in early pregnancy (teratogenicity reported in some studies); otherwise limited data.

Monitoring

• Pruritus response over a 1–2 week trial
• Sedation / anticholinergic effects
• Withdraw before intradermal allergy testing

Toxicity and overdose

Overdose causes pronounced sedation or paradoxical excitation, anticholinergic signs (mydriasis, tachycardia, urinary retention, ileus), and at high doses tremor/seizures and QT effects. Generally a wide margin for ordinary dosing.

Management: No specific antidote. Supportive — manage sedation/excitation, IV fluids; control seizures with benzodiazepines; monitor for anticholinergic complications (bladder, ileus) and cardiac rhythm at high doses. Decontaminate large recent ingestions.

Clinical pearls

• Often the more effective antihistamine for canine allergic itch — worth a 1–2 week trial, but responses are individual
• Its active metabolite is cetirizine, which is why both work for allergic skin disease
• Sedation is common (and sometimes useful) — warn owners; anticholinergic effects can cause urinary retention
• Stop antihistamines before intradermal allergy testing (they blunt the reactions)
• Not a replacement for steroids/oclacitinib in severe atopy — best for mild disease or as an adjunct

Mechanism of action

Competitively blocks peripheral H1 histamine receptors, reducing histamine-mediated pruritus, vasodilation and wheal formation. As a first-generation antihistamine it crosses the blood–brain barrier (central H1 blockade → sedation) and has anticholinergic activity. Its metabolite cetirizine provides additional, less-sedating antihistamine effect.

Formulations and products

• 10 mg tablet
• 25 mg tablet
• Syrup 2 mg/mL (10 mg/5 mL)
• Atarax — 10 / 25 mg tablet; 10 mg/5 mL syrup, Tablet / syrup (human-label)
• Hyzine — 10 / 25 mg tablet, Tablet (human-label)

Storage

Tablets/syrup: 15–30 °C, dry, protect from light.

Before you use this dose

Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

Other hormones, emergency drugs, supplements and other drugs

• Hetastarch (Hydroxyethyl Starch)
• Human Chorionic Gonadotrophin (hCG)
• Hydrocortisone (Cortisol)
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• Hypertonic Saline (7.2–7.5% NaCl)
• Imepitoin
• Insulin
• Intravenous Lipid Emulsion (ILE)

Frequently asked questions