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Hydroxyzine for dogs is an antihistamine that relieves symptoms of allergic reactions. Hydroxyzine was created initially as a sedative for humans. During clinical trials, researchers discovered hydroxyzine had the added benefit of stopping allergic reactions. Further research on hydroxyzine revealed its other applications as an anti-nausea and anti-anxiety medication and found that it was successful at treating these conditions in mammals besides humans.

Though many other antihistamines have come out since its FDA approval, hydroxyzine is still one of the most commonly prescribed medications for allergic reactions and sedation in canines. 

Hydroxyzine's mechanism of action is similar to other first-generation antihistamines in that it prevents histamine from binding to the receptors that instigate allergic responses. These antagonistic effects prevent mild symptoms like itching and sneezing, as well as more severe features like stomach spasms and airway constriction.

Besides being an antihistamine, hydroxyzine's active metabolite also suppresses neurological activity in mammals, making it an effective mild tranquilizer. 

Dosage

A typical dose of hydroxyzine for dogs is 1 mg per pound between 1 and 3 times daily. 

Dosage instructions

Administer hydroxyzine daily as instructed by your vet. If your vet prescribed this medication on an as-needed basis, give it to your pet at the first sign of an impending episode. 

Efficacy

A study of dogs treated with hydroxyzine and chlorpheniramine for atopic dermatitis observed no adverse side effects other than mild drowsiness in the study group. In this study, researchers scored the severity of the dogs’ dermatological symptoms before, during, and after treatment with hydroxyzine and chlorpheniramine. The data collected showed that this drug combination caused a 25% improvement in dermatological symptoms for many of the dogs.

Side effects

The side effects of hydroxyzine resemble those seen with other first-generation antihistamines like Benadryl. Side effects of hydroxyzine include: 

  • Hyperactivity

  • Upset stomach

  • Drowsiness

  • Behavioral changes

  • Sedation

  • Excessive thirst

  • Loss of appetite 

  • Balance issues

  • Seizures

  • Difficulty urinating

  • Tremors

Considerations

Hydroxyzine’s effects on certain neurotransmitters can adversely affect dogs with certain conditions.  

Anticholinergic drugs like hydroxyzine should only be given to pets with epilepsy if medically necessary, since they can increase the likelihood of seizures. In dogs with congestive heart failure, these anticholinergic effects can cause irregular heartbeat and worsen cardiovascular problems. 

This drug may exacerbate glaucoma due to its inhibitory effects on the neurotransmitter acetylcholine, which is responsible for pupil dilation and other eye functions.

Because this medicine causes sedation, it's not recommended for service dogs since it can interfere with their ability to work. Discuss with your vet other non-drowsy alternatives for service animals.  

It's unknown if therapeutic doses of hydroxyzine for dogs are safe during canine pregnancy. Data shows that unusually high doses of this medicine are linked to congenital defects in animal models. Tell your vet if your pet becomes pregnant while taking this drug.

This medication isn’t recommended for nursing dogs, since it can dry up the milk supply. Studies show the active metabolite of hydroxyzine does pass into human breast milk, though it's unknown if this is true for canines or if it affects nursing puppies. 

Hydroxyzine should be also used cautiously in dogs with urinary or intestinal blockages, renal disease, and impaired liver function, since it can aggravate these conditions. 

Drug interactions

Hydroxyzine magnifies the effects of sedatives and inhibits the effect of stimulatory medications. Inform your vet if your dog is taking any of these medications:

  • Anticholinergic agents

  • Nervous system depressants

  • Epinephrine

  • Barbiturates

  • Sedatives

Allergic reactions and sensitivity

Ironically, allergic reactions to antihistamines are actually quite common. Inform your vet of any past reactions to piperazine derivatives or first-generation antihistamines like Benadryl. 

Frequently asked questions

What is the brand name of hydroxyzine for dogs?

The brand names of this medicine are Vistaril and Restall, though generic versions (like hydroxyzine pamoate) are available. This drug was also sold under Atarax and several other names that are no longer manufactured. 

Can I give my dog other allergy medications with hydroxyzine?

Most vets advise against combining hydroxyzine with other antihistamines or tranquilizers since these can intensify sedation. Discuss other medical alternatives with your vet if you feel your dog needs something different. 

When should I give hydroxyzine for my dog's anxiety?

If your vet prescribes this as an emergency medicine for panic attacks, administer at the first signs of an impending attack or before a stressful situation. Outward signs of a panic attack include dilated pupils, trembling, fast pulse, hiding, raised hair, and behavioral changes. 

Is hydroxyzine a treatment for dermatitis?

Yes. Vets often prescribe hydroxyzine for dogs with dermatitis and itchy skin

How long does hydroxyzine work for dogs?

Typically the effects of this medication last for 6 to 8 hours.

Can I buy hydroxyzine for dogs without a prescription?

While some over-the-counter meds contain hydroxyzine (like certain types of Dramamine), it's unknown if these are safe for dogs. Do not give over-the-counter formulations of hydroxyzine unless your vet deems them safe for your pet.


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