# Cetirizine: veterinary dose and monograph

> Cetirizine is a veterinary drug. Second-generation H1 antihistamine — far less sedating than diphenhydramine because it penetrates the brain poorly, with convenient once-daily dosing. Indications include canine atopic dermatitis / allergic pruritus (adjunct); feline allergic / eosinophilic dermatitis; urticaria, mild allergic reactions. This monograph lists 3 reference doses for dogs, cats and horses, each with route, frequency and source.

Source: https://vetmasterji.com/drugs/cetirizine · Last reviewed: 2026-10-01

## At a glance

- **Drug class:** Veterinary drug
- **Also known as:** Zyrtec, Alerid
- **Species with doses:** Dogs, Cats and Horses
- **General dose range:** 0.5–1 mg/kg PO q24h — check the species tables for the indication
- **Routes:** PO
- **Last reviewed:** 1 October 2026

## Indications

- Canine atopic dermatitis / allergic pruritus (adjunct)
- Feline allergic / eosinophilic dermatitis
- Urticaria, mild allergic reactions

## Cetirizine 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

*Cetirizine doses for dogs*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Allergic pruritus | 1–2 mg/kg | PO | q12–24h | — |

- Allergic pruritus: Plumb’s p.245: atopic dermatitis 1 mg/kg PO once daily (Cook 2004); allergic dermatitis 1 mg/kg q12h (Hillier 2004); 0.5–1 mg/kg or 5–10 mg per dog once or twice daily. Papich 5e: 2 mg/kg q12h PO.

### Cats

*Cetirizine doses for cats*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Allergic / eosinophilic dermatitis | 0.5–1 mg/kg | PO | q24h | — |

- Allergic / eosinophilic dermatitis: Papich 5e: 1 mg/kg daily PO — most commonly 5 mg per cat. Plumb’s p.245: 5 mg per cat once daily (Ashley 2009) or q12h for rhinosinusitis (Hawkins & Cohn); pruritus 2.5–5 mg per cat once daily. (2.5–5 mg per cat ≈ 0.5–1 mg/kg for a 5 kg cat.)

### Horses

*Cetirizine doses for horses*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Allergic disease (urticaria, pruritus, RAO adjunct) | 0.2–0.4 mg/kg | PO | q12h | — |

- Allergic disease (urticaria, pruritus, RAO adjunct): Papich 5e and Plumb’s p.245 (Olsen 2008): 0.2–0.4 mg/kg PO q12h, based on equine PK/PD data.

## Contraindications

Significant renal impairment (reduce frequency — renally cleared). Hypersensitivity. Use plain cetirizine — avoid combination products containing pseudoephedrine.

## Adverse effects

- Generally minimal — occasional mild sedation
- Hypersalivation / vomiting in cats (taste)
- Rare GI upset

## Drug interactions

- Minimal — limited hepatic metabolism and few cytochrome-P450 interactions
- Mildly additive sedation with other CNS depressants
- Avoid combination products containing pseudoephedrine

## Pregnancy and lactation

Considered relatively low-risk among antihistamines; use only if needed.

## Monitoring

- Pruritus / lesion response over a 1–2 week trial
- Renal function in impairment (renally cleared — extend the dosing interval)

## Toxicity and overdose

Wide safety margin; overdose mainly causes sedation (occasionally restlessness), and hypersalivation in cats from the bitter taste.

Management: Supportive; no specific antidote needed. Monitor for sedation and manage symptomatically.

## Clinical pearls

- Once-daily and minimally sedating — a practical antihistamine to trial for steroid-sparing in mild atopy
- Antihistamine response is individual; trial for 1–2 weeks before deciding it has failed
- Use plain cetirizine only — combination Zyrtec-D contains pseudoephedrine, which is toxic to pets

## Mechanism of action

Second-generation H1-antihistamine (a carboxylated metabolite of hydroxyzine). Selectively and peripherally blocks histamine H1 receptors with minimal blood-brain-barrier penetration, giving an antipruritic / anti-allergic effect with little sedation, plus mild anti-eosinophil activity.

## Formulations and products

- Cetirizine 10 mg tablet
- Cetirizine 1 mg/mL syrup
- Alerid — 5 / 10 mg tablet; 1 mg/mL syrup, Tablet / syrup (human-label)
- Cetzine — 10 mg tablet; 1 mg/mL syrup, Tablet / syrup (human-label)

## Storage

Store at 15–30 °C, dry.

## Before you use this dose

> **Caution:** 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.

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## Frequently asked questions

### What is the dose of Cetirizine for dogs?

Reference doses for Cetirizine in dogs: 1–2 mg/kg PO q12–24h (Allergic pruritus). Confirm against the label and the patient before use.

### What is the dose of Cetirizine for cats?

Reference doses for Cetirizine in cats: 0.5–1 mg/kg PO q24h (Allergic / eosinophilic dermatitis). Confirm against the label and the patient before use.

### What is the dose of Cetirizine for horses?

Reference doses for Cetirizine in horses: 0.2–0.4 mg/kg PO q12h (Allergic disease (urticaria, pruritus, RAO adjunct)). Confirm against the label and the patient before use.

### When should Cetirizine not be used?

Significant renal impairment (reduce frequency — renally cleared). Hypersensitivity. Use plain cetirizine — avoid combination products containing pseudoephedrine.

### What are the side effects of Cetirizine in animals?

Generally minimal — occasional mild sedation; Hypersalivation / vomiting in cats (taste); Rare GI upset.

## Sources

- Plumb's Veterinary Drug Handbook
- Papich, Papich Handbook of Veterinary Drugs, 5th edition

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VetMasterJi is a clinical decision-support and education platform for veterinary professionals and students. It does not provide veterinary advice, diagnosis or treatment for specific animals. All drug doses, calculators and differentials are references that must be independently verified before clinical use; the attending registered veterinarian remains solely responsible for every clinical decision.