Chlorpheniramine Maleate

What is chlorpheniramine maleate?

Chlorpheniramine maleate (brand names: Chlor-Trimetron®, Aller-chlor®, Chlor-tripolon®, ChlorTabs®) is an antihistamine used to treat allergic conditions and occasionally used as a mild sedative.

Its use in cats, dogs, horses, ferrets, and birds to treat allergic conditions is off label (extra label). Many drugs are commonly prescribed for off-label use in veterinary medicine. “Off label” means the drug is being used in a way that has not been reviewed or approved by the U.S. Food and Drug Administration (FDA) or Health Canada. In these instances, follow your veterinarian’s directions and cautions carefully, as they may be significantly different from those on the label.

How is chlorpheniramine maleate given?

• Chlorpheniramine maleate is given by mouth in the form of a tablet, liquid syrup, or liquid drops.
• Measure liquid forms carefully.
• It can be given with or without food.
• If vomiting occurs when dosed on an empty stomach, give future doses with food.
• This medication is most effective if given regularly and given prior to exposure to the allergen.
• If using an extended-release tablet, do not break, crush, or split the tablets.
• When giving this medication, allow access to water at all times.

If purchased over the counter, read the label carefully before giving this medication to ensure the product contains ONLY chlorpheniramine and liquid products don’t contain xylitol. This medication will take effect quickly, in about 1 to 2 hours, and improvement in clinical signs should follow.

What if I miss giving my pet the medication?

If you miss a dose, give it as soon as you remember, and then continue with the regular dosing schedule. However, if it is almost time for the next dose, skip the missed dose and resume the regular dosing schedule. Do not give the pet two doses at once.

Are there any potential side effects?

Chlorpheniramine maleate may cause the following side effects:

• Sleepiness
• Excitement (in cats)
• Diarrhea
• Vomiting
• Lack of appetite
• Dry mouth
• Mild straining to urinate

Serious adverse reactions may occur. If any of the following signs develop, stop giving chlorpheniramine maleate and contact your veterinarian immediately:

• Seizures
• Abnormal breathing
• Incoordination
• Muscle tremors
• Coma

Other side effects may occur. If you notice anything unusual, contact your veterinarian immediately.  This short-acting medication should stop working within 24 hours, although effects can be longer in pets with liver or kidney disease.

Are there any risk factors for this medication?

DO NOT USE chlorpheniramine maleate in pets that:

• Are allergic to it or other similar antihistamines

USE WITH CAUTION in pets that:

• Have closed-angle glaucoma
• Have enlarged prostate
• Have hyperthyroidism
• Have heart disease or high blood pressure
• Have gastrointestinal or bladder obstruction
• Have obstructive lung disease (COPD)
• Are geriatric, pregnant, or lactating
• Are working dogs

Are there any drug interactions I should be aware of?

Several medications should be used with caution when given with chlorpheniramine maleate, including:

• Anticoagulants
• Central nervous system depressants
• Monoamine oxidase inhibitors (MAOIs)
• Phenytoin

This medication can interact with skin allergy testing; discontinue this medication at least 2 weeks before allergy testing.

Certain medications may interact with chlorpheniramine maleate, so be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking before starting any new treatment.

Is any monitoring needed with this medication?

• Your veterinarian will let you know when and how they want to reassess your pet to ensure the medication is working and not causing side effects.
• At home, monitor for any side effects such as those noted above. If any occur, stop using the medication and contact your veterinarian.

How do I store chlorpheniramine maleate?

• Store the tablets at room temperature between 59°F and 86°F (15°C and 30°C), in a tight container protected from moisture.
• Store the liquid solution at the same room temperature, away from light and protected from freezing.

What should I do in case of emergency?

If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility. Be prepared to provide information about the product and your pet’s weight and symptoms.