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By Wendy C. Brooks, DVM, DipABVP
Educational Director,

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Loratadine (Claritin)

Brand Name: Claritin

Available in 5 mg and 10 mg tablets, and oral syrup


Histamine is an inflammatory biochemical that causes skin redness, swelling, pain, increased heart rate, and blood pressure drop when it binds to one of many H1 receptors throughout the body. Histamine is an important mediator of allergy symptoms in humans, hence a spectacular array of different antihistamines has proliferated. Antihistamines are arranged in different classes based on chemical structure: the ethanolamine class, the ethylenediamine class, the piperazine class, the piperidine class, and the propylamine class. Histamine, perhaps unfortunately, is not as important a mediator of inflammation in pets, which means results of antihistamine therapy are not as reliable in pets as they are in people; however, if a member of one class is not found to be effective, often a member of a different class will be.

The traditional antihistamines on the market are notorious for their drowsiness side effect. Loratadine represents a new generation of antihistamine that does not cross the blood-brain barrier and does not cause drowsiness. It also is much longer lasting than some of the classic antihistamines in use. The size of this tablet and its once or twice a day dosing schedule make it a convenient antihistamine for pet usage. Loratadine, a member of the piperidine class of antihistamines, has gotten relatively positive reviews in particular for treating feline itchy skin, but actual published studies are few.

How this Medication is Used

Loratadine has several important effects and thus several uses. Most obviously, loratadine is an antihistamine and it is used for acute inflammatory and allergic conditions such as:

Loratadine may be included in antihistamine trials for allergic skin disease. In such trials, several antihistamines of different classes are used sequentially in hoping to find one that was especially effective. Often if an antihistamine from one class is ineffective, then one from another class should be tried next. Antihistamines in general are more effective in itchy cats than itchy dogs though some dogs achieve relief with this medication.

Mast cell tumors involve cells that contain granules of histamine. Patients with mast cell tumors experience chronic inflammatory symptoms due to circulating histamine. Traditional antihistamines such as diphenhydramine are used to combat the histamine released by the tumor but loratadine could also be used.

Loratadine can be given with or without food.

If a dose is skipped, do not double up on the next dose.

Side Effects

At doses higher than the recommended dose, human patients complain of headache, drowsiness, and rapid heart rate. In cases of accidental overdose, symptoms include hyperactivity or depression (depending on how much was ingested), and racing heart rate.

Loratadine has been known to decrease tear production in humans so it should be used with caution in dogs with dry eye.

Interactions with Other Medications

In the treatment of allergic skin disease, antihistamines are felt to synergize with omega 3 fatty acid supplements and, as a general rule for this condition, it is best to use these medications together.

Drugs found to increase loratadine blood levels with concurrent use include: ketoconazole (an anti-fungal medication) and erythromycin (an antibiotic). If loratadine is used with either of these medications, drowsiness may result.

Concerns and Cautions

When using an antihistamine to prevent an allergic reaction, such as a vaccine reaction, the antihistamine works best when given prior to the allergen.

This medication has not been evaluated for safety in pregnancy or lactation and thus should not be used in either situation.

This medication will interfere with allergic skin testing. Check with your veterinary dermatologist regarding how far in advance this medication should be withheld.

A formulation called Claritin-D is available combining pseudoephedrine and loratadine. This product is not interchangeable with regular Claritin® and should not be used without specific veterinary guidance. If using human loratadine products, be sure they do not contain additional active ingredients that could be toxic to pets.

Claritin syrup is preserved in propylene glycol and should not be used in cats.

If drowsiness is observed in a patient on loratadine and the patient is not taking concurrent medication that could explain this, then testing of liver and kidney function is in order to search for an explanation. In patients with known liver or kidney disease, the dose of this medication should be adjusted if it is to continue to be used.

Oral disintegrating tablets (also called orodispersible tablets) may contain xylitol, a sweetener that is toxic to dogs.

It is our policy not to give dosing information over the Internet.


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