Loratadine
Ethyl 4-(8-chloro-5,6-dihydro-11H-benzo[5,6]cyclohepta[1,2-b]pyridin-11-ylidene)-1-piperidinecarboxylate
Also known as: Clarityn · Claritin · Alavert · Loratadina · Loratadinum
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Dosing by species
Dosing data for this drug is not yet available in the VetSheet formulary. Every other section below is complete. Consult the current product label before prescribing.
Overview
Loratadine is a second-generation, non-sedating H1-receptor antagonist used in veterinary medicine primarily for the management of allergic conditions such as atopic dermatitis, vaccine reactions, and insect envenomation. Unlike first-generation antihistamines (e.g., diphenhydramine, chlorpheniramine), loratadine does not readily cross the blood-brain barrier, significantly reducing the incidence of central nervous system depression and sedation.
Clinical Warning: Always ensure that human over-the-counter loratadine products do not contain decongestants like pseudoephedrine (often labeled as 'Claritin-D' or 'Allergy & Congestion'), as pseudoephedrine is highly toxic to dogs and cats, potentially causing fatal cardiovascular and neurologic stimulation.
Clinical Pearl: Antihistamines are generally more effective as preventative agents rather than treatments for acute allergic flares, as they block the binding of new histamine but do not displace already bound histamine.
Mechanism of action
Loratadine acts as a selective inverse agonist/antagonist at peripheral H1 histamine receptors.
- Histamine Blockade: It competitively binds to H1 receptors on effector cells in the gastrointestinal tract, blood vessels, and respiratory tract → prevents histamine from binding and exerting its pro-inflammatory and vasodilatory effects.
- Non-sedating: Due to its lipophobic nature and large molecular size, it has poor penetration across the blood-brain barrier, resulting in minimal to no central H1 receptor blockade.
Safety & warnings
Contraindications
- Known hypersensitivity to loratadine or desloratadine
- Use with caution in patients with severe hepatic impairment
- Use with caution in patients with keratoconjunctivitis sicca (dry eye)
Adverse effects
- Mild lethargy or sedation (rare compared to first-generation antihistamines)
- Vomiting
- Diarrhea
- Dry mouth (xerostomia)
- Decreased tear production
Precautions
Use with caution in animals with hepatic impairment, as loratadine is extensively metabolized in the liver. Dose adjustments may be necessary.
Allergy Testing: Antihistamines should be withdrawn at least 1 to 2 weeks prior to intradermal allergy testing to prevent false-negative results.
Drug interactions
May inhibit the metabolism of loratadine, increasing plasma concentrations
May inhibit the metabolism of loratadine, increasing plasma concentrations
May inhibit the metabolism of loratadine, increasing plasma concentrations
May increase loratadine levels via CYP inhibition
Monitoring
- Resolution of allergic clinical signs (e.g., reduced pruritus, erythema)
- Adverse gastrointestinal effects
- Tear production (Schirmer Tear Test) if dry eye is suspected
Pharmacokinetics
Half-life
Absorption
Rapidly absorbed from the gastrointestinal tract after oral administration.
Distribution
Highly bound to plasma proteins (approx 97%). Poor penetration into the central nervous system.
Metabolism
Extensively metabolized in the liver via cytochrome P450 enzymes to its major active metabolite, desloratadine.
Elimination
Excreted roughly equally in urine and feces as metabolites.
Overdose
Loratadine has a wide margin of safety. Massive overdosage may cause tachycardia, somnolence, and headache.
Treatment: Consists of standard gastrointestinal decontamination (emesis induction, activated charcoal) if ingestion is recent, followed by symptomatic and supportive care. Loratadine is not significantly removed by hemodialysis.
Available products
Formulations
- 10 mg tablet
- 1 mg/ml syrup
Human-labeled
- 10 mg tablets (GSL)
- 1 mg/ml syrup (GSL)
Regulatory status
Available OTC for humans.
Available OTC for humans.
Available as a General Sales List (GSL) product in the UK for humans.
No regulatory data for: 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store at room temperature (15-30°C) in tight, light-resistant containers. Protect syrup from excessive heat and freezing.
Client information
Loratadine is an antihistamine used to treat allergies.
- Administration: Can be given with or without food. If vomiting occurs, try giving with a small meal.
- Toxicity Warning: > NEVER give your pet a product containing a decongestant (like pseudoephedrine, often found in 'D' formulations like Claritin-D). These are extremely toxic to pets.
- Expectations: It may take a few days of consistent use to see the full benefit for chronic skin allergies. It is generally less sedating 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.