If your dog is itchy or has an allergic reaction, you may be wondering if antihistamines are the right solution. In this blog post, we will discuss antihistamines for dogs and when they should be used. We will also cover dosage schedules and how antihistamines can be used with other medications. If you're looking for allergy medication for dogs, antihistamines could be a viable option. Make sure to read this post first!

When should antihistamines for dogs be used?

Antihistamines can be used to treat allergies, both seasonal and environmental, and allergic reactions. If your dog is suffering from itchiness, redness, or swelling, antihistamines may be able to help. Antihistamines work by blocking histamine receptors. Histamine is a molecule that is released by the body in response to an allergen. There have been studies that suggest the use of antihistamines for dogs with seasonal allergies is beneficial and the low cost and favorable safety profile of antihistamines make them a popular choice for many dog owners and veterinarians.

It should be noted that not all dogs will respond to antihistamines to provide relief from seasonal allergies. This is because the mediators of the allergic response in dogs are not completely related to histamines. People who suffer from allergies typically have a runny nose, watery eyes, and sneezing as a result of histamine release. These are all symptoms that are not commonly seen in dogs with allergies. Dogs will typically have redness and itchiness of their skin as their main symptoms.

For type-1 hypersensitivity reactions in dogs that result in facial and ocular swelling and hives, such as a bee or wasp sting or vaccine reaction, antihistamines can be beneficial and are typically recommended by veterinarians.

Antihistamines can serve as an effective allergy medication for dogs, especially for those suffering from seasonal or environmental allergies.

Can you combine antihistamines with other medications?

Yes, antihistamines can be combined with other medications for the treatment of allergies in dogs, as long as it is not in addition to another antihistamine. If your dog is taking any other medications, it is important to let your veterinarian know before giving them antihistamines. This includes any supplements that your dog is taking as well. Your veterinarian will be able to tell you if it is safe to give your dog antihistamines and how to do so properly to avoid serious side effects.

Concurrent use of antihistamines for dogs with popular allergy medications such as Apoquel® and Atopica® are safe with no known interactions. Additionally, the use of antihistamines with corticosteroids (e.g. prednisone) can be beneficial as they can reduce the overall dose of corticosteroid that is required. Temaril-P® or Vanectyl-P® are examples of medications that combine prednisone with an antihistamine in one pill.

When considering allergy medication such as antihistamines, it's important to consult your veterinarian, especially if your dog is already on other medications.

What are the commonly used antihistamines for dogs?

The most commonly used antihistamines for dogs include:

  • Diphenhydramine (Benadryl®)
  • Loratadine (Claritin®)
  • Cetirizine (Zyrtec® or Reactine®)
  • Chlorpheniramine (Chlortrimeton®)
  • Hydroxyzine (Vistaril®)

Diphenhydramine (Benadryl®) is the most sedating antihistamine on the list. Cetirizine (Zyrtec® or Reactine®) is one of the most commonly used over-the-counter antihistamines recommended by veterinarians. Claritin® can be used but is not typically recommended by veterinarians as some forms of Claritin® contain decongestants such as pseudoephedrine which is very toxic to dogs.

There is no clear evidence that any one antihistamine works better than another, so other factors can be considered when choosing an allergy medication. These include cost, mode of administration, and side effects (a sedating antihistamine such as diphenhydramine can be administered in the evening instead of in the morning).

What is the typical dosage schedule for antihistamines in dogs?

The typical dosage schedule for antihistamines in dogs is every 8-12 hours, with the exception of cetirizine and loratadine, which are every 24 hours. Medications are dosed based on milligrams (mg) of antihistamine per patient weight in kilograms, i.e. mg/kg.

Diphenhydramine (Benadryl®) dose: The typical dose is 2-4 mg/kg every 8-12 hours.

Loratidine (Claritin®) dose: The typical dose is 0.5 mg/kg every 24 hours.

Cetirizine (Zyrtec® or Reactine®) dose: The typical dose is 1 mg/kg every 24 hours.

Hydroxyzine (Vistaril®) dose: The typical dose is 2-4 mg/kg every 8-12 hours.

🚨 It is important to discuss with your veterinarian if an antihistamine is right for your dog prior to using it.

What are the side effects of antihistamines in dogs?

The most common side effects of antihistamines in dogs include sedation and drowsiness. This is more commonly noticed with first-generation antihistamines such as diphenhydramine (Benadryl®). Newer generation antihistamines such as cetirizine (Zyrtec® or Reactine®) have less of a sedating effect.

At higher doses, a paradoxical reaction can occur, which is an unexpected increase in activity or stimulation. Other possible side effects include loss of appetite, nausea, vomiting, constipation or diarrhea.

When should you not use antihistamines on your dog?

Antihistamines should also be used with caution in dogs that have known sensitivities to antihistamines or have respiratory diseases such as asthma, liver disease, and seizure disorders. Use cautiously in working animals due to the risk of job performance being affected, especially when using first-generation antihistamines such as Benadryl®.

Frequently asked questions about antihistamines for dogs

How much Benadryl® can I give my dog?

The typical dosage for Benadryl in dogs is 2-4 mg/kg of body weight every 8-12 hours. Higher doses greater than 5 mg/kg can have toxic side effects such as seizures, respiratory depression, and cardiovascular effects.

Are antihistamines for dogs safe to use?

Antihistamines are safe to use in dogs when the correct dosages are followed. As many over-the-counter antihistamines may also contain a decongestant such as pseudoephedrine, it is important to read the ingredient list prior to giving it to your dog. Decongestants such as pseudoephedrine are toxic to dogs and need to be avoided.

Can antihistamines for dogs be used to prevent motion sickness in cars?

Yes, while not as effective as maropitant (Cerenia®), antihistamines can be used to prevent motion sickness in dogs. The most common antihistamine used for this purpose is diphenhydramine (Benadryl®). It is best to administer Benadryl® on an empty stomach and 1 hour prior to car travel.

Are antihistamines a good allergy medication for dogs?

Yes, they can be. Antihistamines seem to have the best effect when used for an acute allergy flare-up or when started at the beginning of the allergy season. Starting antihistamines when symptoms have been present for many weeks may not be beneficial for the dog.

Antihistamines for dogs are commonly used to treat allergic reactions and aid in treating seasonal or environmental allergies. When used correctly, antihistamines are a safe and effective way to manage your dog's allergies. Be sure to talk to your veterinarian about the best antihistamine for your dog's individual needs. They will be able to advise which one would be best and at the correct dose for the needs of your dog.