Loratadine — Veterinary Vademecum Drug Reference

Dosage & Administration Guidelines

Species	Route	Dose	Frequency	Duration & Clinical Notes
Dog	PO	0.1-0.5 mg/kg (up to 1 mg/kg in some cases)	q12-24h	Duration: As needed for symptom control; often long-term for chronic allergies Notes: Start at lower end; may be used with other therapies. Response may vary; if no improvement in 2 weeks, reassess.
Cat	PO	0.5-1 mg/kg (or 2.5-5 mg per cat)	q24h	Duration: As needed; may be used long-term Notes: Cats may require higher doses; monitor for sedation (rare).
Horse	PO	0.1-0.2 mg/kg	q12-24h	Duration: As needed Notes: Limited evidence; use with caution.
Rabbit	PO	0.1-0.5 mg/kg	q24h	Duration: As needed Notes: Limited safety data; use with caution.

Clinical Indications & Species Uses

General Indications

Symptomatic relief of allergic reactions
Pruritus of non-infectious origin

Dog (Canine)

Pruritus associated with atopic dermatitis
Allergic dermatitis
Urticaria
Pruritus due to food allergy (adjunctive)

Cat (Feline)

Pruritus associated with allergic dermatitis
Eosinophilic granuloma complex (adjunctive)
Upper respiratory tract infections (as adjunctive for sneezing)

Pharmacology & Mechanism of Action

Drug Class: Second-generation antihistamine (H1 receptor antagonist) | Pharmacological Group: Piperidine derivatives

Mechanism of Action: Loratadine is a selective peripheral H1 receptor antagonist. It blocks the effects of histamine at H1 receptors, thereby reducing allergic symptoms such as pruritus, vasodilation, and increased vascular permeability. It has minimal central nervous system penetration due to its lipophobicity and P-glycoprotein substrate status, resulting in low sedation.

Pharmacodynamics: Loratadine exhibits antihistaminic activity with a rapid onset of action (within 1-3 hours) and a duration of action of at least 24 hours. It has no significant anticholinergic or alpha-adrenergic blocking effects. In veterinary species, it is used to alleviate pruritus associated with atopic dermatitis and other allergic conditions, though its efficacy may be variable.

⚡ Pharmacokinetics Summary

Absorption: Rapidly absorbed after oral administration. Peak plasma concentrations occur within 1-2 hours in dogs and cats. Food may slightly increase absorption but does not significantly affect overall bioavailability.

Distribution: Widely distributed in tissues. Protein binding is approximately 97-99% in humans; in dogs, it is about 97%. It crosses the blood-brain barrier poorly. Volume of distribution is approximately 120 L in humans.

Metabolism: Extensively metabolized in the liver via CYP3A4 and CYP2D6 to its active metabolite, desloratadine. First-pass metabolism is significant.

Excretion: Excreted primarily in urine (approximately 40%) and feces (approximately 40%) as metabolites. The elimination half-life is variable: in dogs, approximately 3-12 hours; in cats, approximately 12-24 hours; in humans, 8-14 hours.

Half-Life: Dogs: 3-12 hours; Cats: 12-24 hours; Humans: 8-14 hours

Bioavailability: Oral bioavailability is approximately 40% in humans due to first-pass metabolism; in dogs, it is approximately 70%.

Protein Binding: 97-99%

Available Formulations & Strengths

Oral Tablet 10 mg (PO)

Oral Tablet (rapid disintegrating) 10 mg (PO)

Oral Syrup 1 mg/mL (5 mg/5 mL) (PO)

Oral Solution 1 mg/mL (PO)

Contraindications & Clinical Warnings

Contraindications:

Hypersensitivity to loratadine or any component
Use with caution in patients with hepatic impairment
Use with caution in patients with renal impairment
Not recommended for use in pregnant or lactating animals unless benefits outweigh risks

Warnings & Clinical Precautions:

May cause mild sedation in some animals, especially cats
Use with caution in animals with cardiovascular disease
May interact with other CNS depressants
In food animals, withdrawal times must be observed; not approved for use in food animals
Do not use in animals with known hypersensitivity to antihistamines
Use with caution in animals with glaucoma, urinary retention, or prostatic hyperplasia (though anticholinergic effects are minimal)

Adverse Effects & Reactions

Common:

Sedation (mild)
Gastrointestinal upset (vomiting, diarrhea)
Decreased appetite

Serious / Severe:

Hypotension
Tachycardia
Seizures (rare)
Hepatotoxicity (rare)

Rare:

Paradoxical excitation
Allergic reactions
Blood dyscrasias

Key Drug Interactions

Interacting Drug / Class	Clinical Effect & Mechanism	Severity
CYP3A4 inhibitors (e.g., ketoconazole, erythromycin)	May increase loratadine plasma concentrations; monitor for adverse effects	Moderate
CYP3A4 inducers (e.g., rifampin, phenobarbital)	May decrease loratadine efficacy	Moderate
CNS depressants (e.g., opioids, benzodiazepines)	Additive sedation	Mild
Amiodarone	May increase risk of QT prolongation	Moderate

Overdose & Toxicity Management

Signs of Toxicity:

Sedation
Tachycardia
Headache
Extrapyramidal effects (rare)
Seizures (in severe cases)

Emergency Treatment Protocol: Induce vomiting if recent ingestion and animal is conscious. Administer activated charcoal to reduce absorption. Provide symptomatic and supportive care, including IV fluids and monitoring of cardiac and neurologic status. There is no specific antidote.

Food Animal Withdrawal Times

Not approved for use in food animals. If used off-label, a withdrawal period of at least 7 days for meat and 7 days for milk is recommended, but consult regulatory guidelines.

Storage, Handling & Regulatory Information

Storage Temperature: Store at room temperature 20-25°C (68-77°F)

Handling & Special Conditions: Protect from moisture; keep in tightly closed container.

Dispensing Status: Over-The-Counter (OTC)

Approval Status: Not FDA-approved for veterinary use; used off-label in animals.

Extra-Label (Off-Label) Use: In the US, loratadine is available over-the-counter for human use. In veterinary medicine, it is used off-label; extra-label use in food animals is prohibited unless under veterinary supervision with appropriate withdrawal times.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Loratadine is a second-generation antihistamine that is generally well-tolerated in dogs and cats. It is less sedating than first-generation antihistamines like diphenhydramine. Clinical response is variable; some animals may not respond adequately. It is often used as an adjunct to other therapies (e.g., fatty acids, corticosteroids) for allergic dermatitis. In cats, it may be useful for upper respiratory signs. Doses should be adjusted based on response and tolerability. Monitor for adverse effects, especially in animals with hepatic or renal impairment. Always consider the potential for drug interactions.

References & Literature

📚 Plumb's Veterinary Drug Handbook
📚 Papich Veterinary Pharmacology and Therapeutics
📚 Compendium of Veterinary Products (CVP)