CHLORPHENIRAMINE MALEATE

(for veterinary information only)

BRAND NAME: CHLOR-TRIMETON

AVAILABLE IN
2 mg, 4 mg, 8 mg, 12 mg & 16 mg
TABLETS
AS WELL AS
ORAL SYRUP
AND INJECTABLE

BACKGROUND

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 a very important mediator of allergy in humans, hence a spectacular array of different antihistamines has proliferated. 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.

HOW THIS MEDICATION IS USED

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

• Vaccination reactions
• Blood transfusion reactions
• Bee stings and insect bites
• The management of itchy skin

Chlorpheniramine maleate is frequently included in antihistamine trials for allergic skin disease. It is not one of the more effective antihistamines in dogs but is one of the most reliably effective antihistamines in the cat (in one study 73% of itchy cats responded). Its availability and inexpensiveness make it worth trying in many cases. Antihistamines are best used in a long term setting as a preventive rather than in an acute setting where inflammation is already active.

Mast cell tumors are tumors involving cells which contain granules of histamine. Patients with mast cell tumors experience chronic inflammatory symptoms due to circulating histamine. Antihistamines such as chlorpheniramine maleate may be helpful given long term.

Chlorpheniramine maleate causes drowsiness in animals just as it does in people and can be used as a mild tranquilizer. Some argue that it is the drowsiness side effect that makes this medication appear to be helpful in itch management (i.e. patients scratch less because they are sleeping more.)

Convenient dosing, tablet size, and tablet strength make it a common choice in the cat; however, its very bitter taste may make its use problematic for cats.

Chlorpheniramine maleate is typically administered 2-3 times daily.

SIDE EFFECTS

With so many possible uses of this medication, it is difficult to separate out a side effect from a primary effect. Drowsiness is generally regarded as an undesirable side effect.

At doses higher than the recommended dose, human patients complain of dry mouth and experience difficulty with urination. Animal patients experiencing dry mouth may drink more water.

Chlorpheniramine maleate is famous for bitter taste. Often the pet (especially cats) will tolerate the medication for a period of time but ultimately refuse to take it or even show salivation in response to administration. In such cases, it may be best to try a different medication.

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.

Chlorpheniramine maleate should not be used with additional tranquilizing medications.

This antihistamine is used in an assortment of human products where it is combined with pain relievers or decongestants and antihistamines. These “combination” products should not be used in animals.

Drugs considered Monoamine Oxidase Inhibitors can promote the potential for dry mouth & difficulty urinating. Monoamine Oxidase inhibitors are not commonly used in pets with the exception of amitraz, which is included in some tick prevention products (click here to see which ones) and selegiline, which is used chiefly for cognitive dysfunction.

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

Antihistamines should be used with caution in patients with high blood pressure, hyperthyroidism, heart disease, or who are at risk for urinary obstruction.

Page last updated: 6/3/2019