Cetirizine
Cetirizine HCl
Also known as: Zyrtec · Piriteze · Zirtec · UCB-P071 · P-071 · cetirizina · cetirizini · ceterizino · Cetirizine hydrochloride · Cetirizinum
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| For atopic dermatitis | 1 mg/kg PO once daily with or without food | PO | q24h | — | 🌎 NA |
| For atopic dermatitis | 5-10 mg (total dose) PO once daily | PO | q24h | — | 🌎 NA |
| For allergic dermatitis | 1 mg/kg PO q12h | PO | q12h | — | 🌎 NA |
| For adjunctive treatment of pruritus | 0.5-1 mg/kg or 5-10 mg total dose once to twice daily | PO | q12-24h | — | 🌎 NA |
- For atopic dermatitis: Satisfactory control of pruritus in 18% of dogs evaluated in the study.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| For adjunctive treatment of non-responsive chronic rhinosinusitis | 5 mg (total dose) PO q12h | PO | q12h | — | 🌎 NA |
| General antihistamine use | 5 mg (total dose) per cat PO once daily | PO | q24h | — | 🌎 NA |
| For adjunctive treatment of pruritus | 2.5-5 mg (total dose) per cat once daily | PO | q24h | — | 🌎 NA |
- General antihistamine use: No controlled studies evaluating effectiveness against other antihistamines.
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Antihistamine | 0.2-0.4 mg/kg PO q12h | PO | q12h | — | 🌎 NA |
- Antihistamine: Based on pharmacokinetic and pharmacodynamic data, may be a useful antihistamine in horses.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Cetirizine is a second-generation antihistamine widely used in human medicine and increasingly utilized in veterinary practice for the adjunctive management of allergic and histamine-mediated pruritic (itchy) conditions.
- Non-sedating profile: Unlike first-generation antihistamines (e.g., diphenhydramine, chlorpheniramine), cetirizine poorly penetrates the blood-brain barrier at standard doses, resulting in significantly less sedation.
- Active metabolite: It is a piperazine-class derivative and the primary active human metabolite of hydroxyzine.
- Clinical utility: Primarily used for atopic dermatitis in dogs and cats, adjunctive treatment of chronic rhinosinusitis in cats, and occasionally for allergic conditions in horses. While antihistamines are generally less effective as monotherapy for severe allergic flares in pets compared to humans, they are valuable as part of a multimodal, steroid-sparing approach.
Mechanism of action
Cetirizine acts as a highly selective, competitive antagonist at peripheral H1 receptors.
- Allergic cascade: Allergen exposure → Mast cell/basophil degranulation → Histamine release → Binds to H1 receptors on sensory nerve endings and blood vessels → Pruritus, vasodilation, and edema.
- Cetirizine competitively blocks this binding, preventing histamine-mediated effects.
- It also appears to decrease histamine release from basophils in some species, though experimental studies in cats showed it does not reduce eosinophilic airway inflammation.
- It lacks significant anticholinergic or anti-serotonergic activity, and tolerance to its antihistaminic effects is not thought to occur.
Safety & warnings
Contraindications
- Hypersensitivity to cetirizine or hydroxyzine
- Combination products containing pseudoephedrine (e.g., Zyrtec-D) are strictly contraindicated in dogs and cats
Adverse effects
- Vomiting
- Hypersalivation (drooling)
- Somnolence (drowsiness/sedation, especially in small dogs at higher dosages)
- Dry mouth (reported in humans)
Precautions
CRITICAL WARNING: Combination products containing pseudoephedrine (e.g., Zyrtec-D) are highly toxic to dogs and cats and must never be used.
- Organ Impairment: Dosage adjustment is recommended in patients with severe renal or hepatic impairment, as the drug is primarily excreted unchanged in the urine.
- Allergy Testing: Discontinue medication well in advance of any hypersensitivity (intradermal) skin testing to avoid false-negative results.
- Pregnancy/Nursing: Categorized as FDA Category B in humans. Approximately 3% of a dose is excreted into milk in Beagles; while probably safe, caution is advised in nursing animals.
Drug interactions
Additive CNS depression if used concurrently with cetirizine
Monitoring
- Clinical efficacy (reduction in pruritus or allergic signs)
- Adverse effects (vomiting, hypersalivation, somnolence)
Pharmacokinetics
Half-life
Absorption
In humans, peak concentrations occur in about 1 hour. Food can delay, but not affect the extent of, absorption.
Distribution
In cats, volume of distribution is 0.26 L/kg. It is 93% bound to human plasma proteins. Brain levels are approximately 10% of those found in plasma, explaining its non-sedating nature.
Metabolism
It is a human metabolite of hydroxyzine.
Elimination
In cats, clearance is about 0.3 mL/L/minute. In humans, approximately 80% is excreted in the urine, primarily as unchanged drug.
Overdose
Cetirizine generally has a wide margin of safety.
- Massive Overdose: May cross the blood-brain barrier in overdose situations, leading to neurologic signs (hyperactivity or severe sedation).
- Cardiovascular Safety: Unlike earlier non-sedating antihistamines (terfenadine and astemizole), cetirizine does not appreciably prolong the QT interval on ECG at high serum levels.
-
TOXICITY ALERT: Overdoses of cetirizine products that also contain pseudoephedrine (e.g., Zyrtec-D 12 Hour) are highly dangerous and potentially fatal. Immediate veterinary intervention and consultation with an animal poison control center are required.
Available products
Formulations
- Oral Tablets (film-coated)
- Chewable Tablets
- Oral Syrup
- Extended-Release Tablets (with Pseudoephedrine - CONTRAINDICATED IN PETS)
Veterinary
- None (No veterinary-labeled products available)
Human-labeled
- Cetirizine HCl Oral Tablets (film-coated): 5 mg & 10 mg (Zyrtec, generic)
- Cetirizine HCl Chewable Tablets (grape flavor): 5 mg & 10 mg (Zyrtec)
- Cetirizine HCl Oral Syrup: 1 mg/mL in 118 & 473 mL (Zyrtec, generic)
- Cetirizine HCl 5 mg with Pseudoephedrine HCl 120 mg Extended-Release Tablets (Zyrtec-D 12 Hour) - DO NOT USE IN PETS
Regulatory status
Available as an over-the-counter human medication.
GSL (General Sales List) - available over the counter.
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Tablets should be stored at 20-25°C (68-77°F); excursions are permitted to 15-30°C (59-86°F). The oral syrup may be stored at room temperature or in the refrigerator.
Client information
Cetirizine is an antihistamine commonly used to help manage allergic skin disease, itching, and sometimes respiratory allergies in pets.
- Administration: Can be given with or without food. If your pet vomits after taking it, try giving the next dose with a small treat or meal.
- Side Effects: Generally very well tolerated. Mild sleepiness, drooling, or occasional vomiting may occur. If your pet seems excessively drowsy, contact your veterinarian.
-
CRITICAL WARNING: Only use plain cetirizine. Never give your pet "Zyrtec-D" or any product containing decongestants like pseudoephedrine. These ingredients are extremely toxic and potentially fatal to dogs and cats.
- Allergy Testing: If your pet is scheduled for allergy skin testing, ask your veterinarian when you should stop giving this medication beforehand, as it can interfere with the test results.
- Cost: While generic options are available, it may be more expensive than older antihistamines like Benadryl.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.