Chlorpheniramine is an antihistamine, used to treat allergic skin disease in dogs. Although it is a human drug and not labelled for use in pets, it is often used in dogs and other animal species to provide relief from the effects of allergies. 

While it is not effective for every dog, it can help alleviate clinical signs of itching and skin inflammation in some canines. 

What is Chlorpheniramine?

Chlorpheniramine is a first-generation antihistamine that was developed for human use in 1948. Over seventy years later, it is still available as an over-the-counter medication to treat seasonal allergies in humans. 

In addition to its use in human medicine, chlorpheniramine has also been used as an allergy medicine for dogs. The use of human chlorpheniramine in dogs is “off-label,” which means that it is not specifically labelled for use in dogs. Therefore, chlorpheniramine should be given only under the supervision of a veterinarian. 

While chlorpheniramine is not effective for every dog, it does provide relief for some dogs with mild allergic skin disease. 

What Does Chlorpheniramine Look Like?

Chlorpheniramine maleate is typically administered as a small, round yellow tablet that is scored down the middle. It is also available as a syrup, as well as in flavored chews and capsules that vary in appearance based on the compounding pharmacy.

How Does It Work for Dogs?

Chlorpheniramine is an antihistamine, like diphenhydramine (Benadryl). This means that it counteracts the activity of histamine, a key mediator involved in allergic disease. During an allergic reaction, histamine is released and it is this histamine that is responsible for the itching and inflammation that is associated with many allergic reactions in dogs. When the action of histamine is blocked by an antihistamine, an allergic reaction can be prevented, halted, or decreased in severity. 

In dogs, chlorpheniramine has variable efficacy. Some dogs experience a dramatic improvement in skin allergies with chlorpheniramine, while others will show no apparent benefit with treatment. In many cases, trial and error is required to determine the optimal medication to treat canine skin allergies. Chlorpheniramine may be combined with other medications, such as corticosteroids or fatty acid supplements. 

While human chlorpheniramine is often used as an antihistamine for dogs, it’s important to exercise caution when purchasing chlorpheniramine from your local pharmacy. Chlorpheniramine is often combined with decongestants, pain relievers, or other medications that may be toxic to dogs. If your veterinarian has recommended that you purchase over-the-counter chlorpheniramine for your dog, read labels carefully and consider talking to a pharmacist to ensure that you are purchasing a product that contains only chlorpheniramine. 

What Is Chlorpheniramine Used For in Dogs?

Chlorpheniramine is used to treat allergic skin disease. Although it is not typically effective in dogs with food allergies, chlorpheniramine may be used to treat itching associated with:

• Atopic dermatitis (seasonal skin allergies)
• Contact dermatitis  
• Flea allergic dermatitis (must be combined with effective flea prevention)

Chlorpheniramine Side Effects in Dogs

Like any antihistamine, especially other first-generation antihistamines, chlorpheniramine may cause sedation. Dogs may become tired or act weak while taking chlorpheniramine. In some cases, this resolves over the course of a few days as the dog acclimates to the medication. In other cases, sedation persists and the medication must be stopped. 

In rare cases, dogs may become excitable or agitated when treated with chlorpheniramine. Dogs with a seizure disorder may also be more likely to have a seizure while on chlorpheniramine. Treated dogs may also develop gastrointestinal effects, including vomiting and diarrhea, especially if chlorpheniramine is given on an empty stomach.

Discontinue your dog’s chlorpheniramine and contact your veterinarian if you notice any of the following side effects: 

• Significant sedation
• Ataxia (trouble walking) 
• Significant excitability
• Seizures
• Concerning behavior changes
• Decreased appetite
• Nausea/vomiting
• Diarrhea
• Increased skin inflammation (which could indicate an allergic drug reaction)
• Eye redness, pain, or squinting (which could indicate a drug-induced decrease in tear production)

Many dogs safely take chlorpheniramine for prolonged periods of time with no negative effects. 

Reactions With Other Drugs and Medications

Chlorpheniramine may enhance the effects of a number of other drugs, including pseudoephedrine, amitraz, selegiline, and sedatives that act on the central nervous system. Therefore, chlorpheniramine should be used with caution in dogs receiving these medications. 

Taking chlorpheniramine in combination with antacids may decrease the body’s ability to absorb chlorpheniramine. Taking chlorpheniramine in combination with certain antibiotics and antifungal agents may increase circulating levels of chlorpheniramine, increasing the likelihood of side effects. 

Chlorpheniramine can also interfere with the results of skin allergy testing. If your dog will be receiving allergy testing, chlorpheniramine should be stopped two weeks prior to testing. 

Chlorpheniramine Dosage for Dogs

Your dog’s recommended chlorpheniramine dose will depend on his size, the severity of his allergic condition, his overall health status, and any other medications he is taking. 

Follow your veterinarian’s dosing recommendations when giving chlorpheniramine. If you have any questions or concerns about your dog’s chlorpheniramine dose, contact your veterinarian before making dosage changes on your own. 

What if My Dog Misses a Dose of Chlorpheniramine?

Chlorpheniramine is typically administered every 8-12 hours. If you miss a dose, you have two options. You could give the missed dose as soon as you realize it, then administer the next dose 8-12 hours later. Alternatively, you could skip the missed dose completely and give the next dose at its scheduled time. Either option is reasonable, depending on the severity of your dog’s allergies and when you notice the missed dose. 

Price of Chlorpheniramine for Dogs

Generic chlorpheniramine is typically very inexpensive. Depending on the size of your dog and where you purchase the medication, you can expect to spend anywhere from $5-$20 per month for your dog’s chlorpheniramine. 

Chlorpheniramine Storage Instructions

Chlorpheniramine tablets, syrup, flavored chews, and capsules should be stored at room temperature. They do not require refrigeration.