Hydroxyzine hydrochloride (HCl) is a medication that is used for the management of the symptoms associated with allergies. It is critical to understand that it doesn’t cure or treat allergies since the health condition is a multifactorial phenomenon that typically involves an inappropriately hyperactive immune response.

Hydroxyzine HCl is an antihistamine that is not approved by the FDA for any form of veterinary treatment. However, its continuing use in the management of canine allergies has clearly made this off-label indication to be quite acceptable to many dog owners. As such, it is imperative that you only use it with the expressed guideline coming from your veterinarian.

Hydroxyzine is the active ingredient of several brands of antihistamines. Common brands that have hydroxyzine as their principal ingredient include Atarax, Anxanil, and Vistaril.

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The indications of hydroxyzine are closely related to its antihistaminic effects. Since histamine receptors are found abundantly in a dog’s body, one can always expect effects that are not necessarily part of its written indication, but nevertheless can provide for some clinical benefit. The following are some of the more common clinical indications of hydroxyzine. Again, please bear in mind that these are off-label indications since it is not approved by the FDA for use in animals.

  • Symptomatic management of allergic reactions in dogs

The primary off-label indication of hydroxyzine HCl for dogs is the management of the symptoms of allergic reactions such as what typically happens in insect bites, snake bites, reactions to pet vaccines, and other causes of inflamed, itchy skin in dogs. It should be noted that while hydroxyzine can help mitigate the various manifestations of allergies, it does not cure the disease itself since this requires a very methodical approach that typically involves taming a hyper-reactive immune system in pooches. At the very least, your dog will not have to keep on scratching which can lead to cuts on its skin. These cuts can become entry points for bacteria as well as other pathogenic microorganisms leading to secondary infections.

  • Sleeplessness in pooches 

Like most antihistamines, hydroxyzine easily passes through the blood-brain barrier where it can exert its physiologic effects. One of these is somnolence or sleepiness. It is for this reason that hydroxyzine can also be used on dogs that may be suffering sleeplessness. This can be very beneficial especially if your dog is not having enough or plenty of rest that it needs to recuperate. However, since hydroxyzine is geared for symptom management, effort must still be exercised in determining the actual cause of canine sleeplessness in dogs so that the appropriate treatment can be identified and implemented.

  • Restlessness in dogs 

Hydroxyzine has weak antianxiety properties owing to its action against serotonin receptors in the dog’s central nervous system. This helps provide for a calming and relaxing effect which can be exceptional in dogs that are quite hyperactive or are particularly restless because of the manifestations of allergies.

Benefits of Hydroxyzine

Hydroxyzine for dogs can provide a host of benefits that is inherently tied to its being an antihistamine as well as antiserotonin. We’ve listed below some of the more common benefits of this drug for dogs.

  • Alleviates the symptoms of allergies 

Itching, rashes, and hives are just some of the more common manifestations of canine allergies. At any rate, your dog will not have to endure the itch anymore. Since itching is a very unpleasant and downright annoying experience, you can at least be more confident that your pooch won’t have to experience these manifestations of allergy while it is undergoing therapy with hydroxyzine.

  • Helps prevent secondary bacterial infections 

Intense itching may look so benign that there is no immediate danger to it. Unfortunately, this is far from the truth since intense itching will stimulate the dog to scratch its skin, especially the itching portions of its body. Frequent scratching can lead to further inflammation of the skin. This undermines the skin’s integrity, thinning it, and risk removing the topmost barrier of the skin. In many cases, sharp nails from your dog’s paws can injure the skin providing a passageway for bacteria to invade the underlying tissues of the skin. This can lead to secondary bacterial infections. Since hydroxyzine helps alleviate the itching, your dog won’t scratch its skin, hence, preventing the development of secondary bacterial infections.

  • Promotes rest and sleep in dogs 

The antihistaminic effects of hydroxyzine have a very welcome side effect – somnolence or sleepiness. Together with its weak effects on serotonin receptors, hydroxyzine can help pooches feel more relaxed and be able to sleep better. This can be crucial to the healing process, allowing their bodies to heal properly.

  • Enhances canine well-being 

The mere fact that the clinical signs and symptoms of allergy have been mitigated by hydroxyzine, your pooch will be able to resume its activities of daily living. It will be able to enjoy playing with you, going out for a walk, and even eating its favorite meal. This can easily translate to greater well-being for your canine friend.

dog in nature

How Hydroxyzine Works

Hydroxyzine is a very potent antihistamine. Technically, it works as a selective inverse agonist of histamine (H1) receptors. Unlike other antihistamines in the market, especially the 1st generation of antihistamines, Hydroxyzine does not affect muscarinic acetylcholine receptors which make it free from the anticholinergic effects of these substances that are commonly seen in first generation histamine inverse agonists. It should be understood that hydroxyzine is not really an antihistamine, meaning it doesn’t really go against histamine itself. What hydroxyzine does is that it binds to the same receptors that Histamine type 1 cells bind to. Once it binds to these receptors, it produces a host of reactions or physiologic effects that are the direct opposite of what normal histamine-1 would do.

Experts say that histamine type 1 receptors promote the expression of a transcription factor, known as NF-kB, which effectively regulates the inflammatory process. Because allergic reactions are typically manifested by a host of inflammatory responses often mediated by histamine, if the transcription factor can be attenuated from its full expression, then there will be lesser frequency and intensity of allergic manifestations. We did not say complete elimination of allergic symptoms since there are clearly other pathways upon which allergic processes can occur or develop. There is only attenuation or the weakening of the expression of the NF-kB transcription factor, not its complete antagonism. Furthermore, since hydroxyzine is clinically approved for use on humans, not dogs, it is quite questionable whether such mechanisms of action seen in humans are the same with dogs.

In addition to its effects on histamine type 1 receptors, hydroxyzine is also believed to have a weak antiserotonergic, antiadrenergic, and antidopaminergic effects. It is its weak antiserotonergic property that can also help hydroxyzine provide a calming effect on dogs that may experience increased itching or any other manifestation of mild to moderate allergies.

Potential Side Effects

Some of the more common side effects that are associated with the administration of hydroxyzine to dogs are related to the many physiologic properties of the drug, often related to its antihistaminic properties as well as its effects on other physiologic mechanisms. The following have been commonly reported.

  • Sedation or sleepiness
  • Vomiting
  • Increased thirst
  • Lethargy
  • Weakness
  • Diarrhea
  • Loss of appetite

Other signs may be present, however. If you see any of the following manifestations, it is important to cease giving hydroxyzine to your dog and call your veterinarian immediately or, better yet, bring your pooch to a veterinary facility with emergency care services.

  • Difficulty breathing or labored breathing
  • Swelling on your dog’s face, lips, and tongue
  • Itchy, red, and raised welts on your dog’s skin

Things You Should Know about Hydroxyzine

Hydroxyzine is not approved by the FDA for use in the management of allergic manifestations in dogs. However, this has not prevented veterinary practitioners from actively recommending and prescribing it to their respective canine patients. Hydroxyzine is the name of the active ingredient that is found in a group of selective H1 receptor reverse agonists. These are available in tablet, capsule, and syrup formulations, although the human preparation also comes with an injectable formulation. It is known that in some cases of severe allergic reactions in dogs where immediate relief of its manifestations is a desired outcome, injectable hydroxyzine can be administered but only by your licensed veterinarian. Because of the off-label use of hydroxyzine in pets, it is important to listen and adhere to your vet’s instructions as it can be quite harmful to provide your dog with a medication that is inherently designed for humans.

What You Should Tell Your Vet before He Prescribes Hydroxyzine

If your pooch is known to be allergic to antihistamines, it is best to tell your veterinarian about it. Also, if your dog has been diagnosed with glaucoma, lung disease, enlargement of the prostate, high blood pressure, or heart disease, then your veterinarian has the right to know about these conditions as well. While hydroxyzine is generally considered as safe, it should never be administered to dogs that are pregnant as well as those that are nursing puppies. If your pooch has intestinal obstruction or even urinary tract obstruction, your vet may have to provide you with additional instructions on how to properly administer hydroxyzine to these dogs.

dog medication

How to Give Hydroxyzine to Your Dog

Hydroxyzine HCl for dogs is an F anti-allergy formulation that is primarily intended for humans, not dogs. However, because it has been used for a long time with very minimal untoward reactions seen in dogs, many veterinarians recommend giving it to pooches. It is available in tablet, syrup, and capsule forms. In some cases, it is also available in injectable presentations. The tablet and / or capsule formulation of hydroxyzine HCl for dogs is available in the following dosages:

  • 10 mg
  • 25 mg
  • 50 mg
  • 100 mg

Hydroxyzine HCl for dogs is also available in syrup form in the following dosages:

  • 2 mg per mL

The injectable formulation is available in the following concentrations

  • 25 mg per mL
  • 50 mg per mL

If your veterinarian orders for hydroxyzine to be administered via the oral route, the usual dosage recommendation is 2 milligrams per kilogram or roughly 1 milligram per pound of doggie body weight. The dose is to be given 3 to 4 times daily or every 6 to 8 hours. It should be understood that the duration of the hydroxyzine treatment is largely dependent on the clinical condition of your pet pooch. It is generally recommended that you finish the course of treatment for your dog even though your pet may already show signs of improvement.

What to Do If You Miss a Dose

Missing a dose requires you to administer the missed dose at once. However, if the time of noticing the missed dose is already close to the next scheduled dose administration, then you can forget the missed dose entirely. If there is anything that you shouldn’t do in a missed dose, then that would be doubling on the next scheduled dose.

What to Do in Case of Hydroxyzine Overdose

It is not uncommon to have adverse reactions or even toxicities to hydroxyzine especially since the drug is not really meant for dogs or animals. If any of the adverse or hypersensitivity reactions we have outlined above does appear, calling your vet or even rushing your pet to a vet facility with emergency services is a must.

Some Drug Interactions

Dogs that are currently receiving epinephrine, tranquilizers, and barbiturates should not be given hydroxyzine as there have been incidences of adverse interactions when given concomitantly with these canine medications. Also, if your canine friend is receiving drugs like monoamine oxidase inhibitors, CNS depressants, or even anti-wheezing medications, your dog can still take hydroxyzine but with due caution.

Hydroxyzine is a very potent antihistamine. Unfortunately, it was not designed to be given to dogs. Just because vets have been prescribing it and dog owners have been giving it to their dogs for many years doesn’t mean that your pooch will be perfectly safe. If you do decide to push through with the use of hydroxyzine for your dog, then be sure to stick to the guidelines and recommendations outlined by your veterinarian.

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Olivia Williams
Olivia is our head of content for MyPetNeedsThat.com, mum of one and a true animal lover. With 12 different types of animal in her family, it's never a dull moment. When she isn't walking the dogs, feeding the cats or playing with her pet Parrot Charlie, you will find her product researching and keeping the site freshly updated with the latest products for your pets!


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