If you have noticed that your dog has been itching or has been diagnosed with allergies, you might wonder if you can give an antihistamine to help control the symptoms. In this blog post, I will discuss the use of antihistamines in dogs, what doses to use, as well as other things you should be aware of, such as side effects, and when they should be avoided altogether.
When should antihistamines for dogs be used?
I typically use antihistamines to treat allergic reactions in dogs, but they can also have some benefits in treating seasonal and environmental allergies.
Antihistamines work by blocking histamines, which are released during the allergic response. If you notice any swelling, especially around the face, during an allergic reaction or flare-up, histamines are often a contributing culprit.
The drawback of using antihistamines in dogs, especially for seasonal or environmental allergies, is that not all dogs will respond. This is likely because histamines are often a very small component of the allergy symptoms. I have found that when dogs have a runny nose, alongside itchy skin, they are more likely to respond to an antihistamine.
For type-1 hypersensitivity (allergic) reactions in dogs that cause swelling of the face and eyes, as well as hives, from something such as bee/wasp stings or a vaccine reaction, I often use antihistamines.
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.
Can you combine antihistamines with other medications?
Yes, antihistamines are safe with other medications. The only time you would want to avoid combining would be with other antihistamines, Temaril-P® or Vanectyl-P. Please inform your veterinarian of every medication or supplement you are giving your dog, so they can make sure antihistamines will not have any current drug conflicts.
You can safely use antihistamines alongside other allergy medications such as Apoquel® and Atopica®, as there are no known interactions. Additionally, we are able to combine antihistamines with corticosteroids such as prednisone or dexamethasone for those patients who need both.
If you are considering using antihistamines in your dog, it would be best to contact your veterinarian to make sure it will be safe for your dog.
What are the commonly used antihistamines for dogs?
The most commonly used antihistamines for dogs that we use 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 also be used, but many forms of Claritin contain pseudoephedrine, which is a decongestant and is very toxic to dogs. If you are looking for Claritin, make extra sure it does not contain this ingredient.
If you are wondering which antihistamine works best, there is no clear evidence that one is better than the other. The response appears to be very individual, where one will work better for one dog, and a different antihistamine will work better for another. Factors to consider when choosing would be the degree of sedation and cost.
What is the typical dosing schedule for antihistamines in dogs?
The usual dosing schedule for antihistamines in dogs is every 8-12 hours, with the exception of Claritin and Zyrtec/Reactine (cetirizine and loratadine, respectively), which are every 24 hours.
We dose antihistamines based on mg per kg of body weight (i.e. mg/kg).
Diphenhydramine (Benadryl®) dose: The common dose is 2-4 mg/kg every 8-12 hours.
Loratidine (Claritin®) dose: The common dose is 0.5 mg/kg every 24 hours.
Cetirizine (Zyrtec® or Reactine®) dose: The common dose is 1 mg/kg every 24 hours.
Hydroxyzine (Vistaril®) dose: The common 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 common with first-generation antihistamines such as Benadryl (diphenhydramine). Zyrtec, Reactine, or Claritin are newer generation antihistamines, and have less sedating effects.
When using higher doses, an unexpected increase in activity or stimulation can occur. Other possible side effects include loss of appetite, nausea, vomiting, constipation or diarrhea.
When should you not use antihistamines on your dog?
I would be hesitant to use antihistamines in dogs that have respiratory conditions such as asthma or bronchitis, liver disease, and seizure disorders such as epilepsy.
Keeping in mind that antihistamines can be sedating, avoid them during planned strenuous activities, such as swimming.
Frequently asked questions about antihistamines for dogs
How much Benadryl® can I give my dog?
The recommended dose 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 generally very safe for dogs when the correct dose is used.
As some antihistamines may also contain a decongestant such as pseudoephedrine, it is important to read the label to ensure you do not accidentally give this to your dog.
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 reason 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 helpful to your dog.