Hydroxyzine
(hye-drox-i-zeen)

• Category: Antihistamine
• Other Names for this Medication: Atarax®, Vistaril®
• Common Dosage Forms: Veterinary: None.

Use only products that contain hydroxyzine as a single active ingredient. Any other ingredients (eg, pain relievers, decongestants) found in human-label combination products can be toxic to animals.

Antihistamines are normally used on an ongoing basis in animals thatrespond to them. They work better if used before exposure to an allergen (eg, pollens).

Most common side effectis drowsiness or sleepiness, butthis may be useful in itchy animals.

Dry mouth, decreased gastrointestinal activity, and trouble urinating are possible. May be given with or withoutfood. If your animal drools, vomits, or acts sick after getting it on an empty stomach, give with food or small treatto see if this helps. If vomiting continues, contact your veterinarian.

Uses/Indications:

Hydroxyzine is a first-generation antihistamine that may be useful in dogs and cats for the adjunctive treatment of histamine-mediated pruritic and allergic conditions (eg, urticaria, insect bite hypersensitivity) and atopy. It also has sedative and tranquilization effects. Guidelines for atopic dermatitis treatment in dogs state that antihistamines have modest efficacy; hydroxyzine should be given continuously (ie, daily) as preventative therapy before an acute flare.

The response to hydroxyzine, as with other antihistamines in dogs and cats, is individualized and not predictable. One patient may respond to one antihistamine but not another. Better results might be obtained if hydroxyzine is combined with chlorpheniramine, as this combination has been reported to be effective in reducing the clinical signs of canine atopic dermatitis in ≈1 of 3 treated dogs, and pruritus improved by more than 25% in 10 of 17 dogs.

This class of drugs may also be used as adjunctive therapy for mast cell tumors and to prevent local histamine release during surgical excision of mast cell tumors.

Because of its CNS depressant effects, hydroxyzine may also be of benefit as a mild sedative in small animal species.

How is this medication useful? 

Hydroxyzine blocks histamine’s effects to reduce itchiness associated with allergies. Allergies that cause histamine release, which causes itchy skin.

• It can also be used as treatment for itching related to certain types of cancers (eg, mast cell tumors).
• Like other antihistamines, the response to this drug can vary between animals and be unpredictable, so your veterinarian may try several different antihistamines to see which one works best for your animal. Hydroxyzine may be used with another antihistamine to improve its effects.

The FDA has approved this drug for use in humans, but it is not officially approved for use in animals.

The FDA allows veterinarians to prescribe products containing this drug in different species or for other conditions in certain situations.

You and your veterinarian can discuss why this drug is the most appropriate choice.

What should I tell my veterinarian to see ifthis medication can be safely given?

Many things might affect how well this drug will work in your animal. Be sure to discuss the following with your veterinarian so together you can make the besttreatment decisions.

• Other drugs can interact with hydroxyzine, so be sure to tell your veterinarian and pharmacist what medications (including vitamins, supplements, or herbal therapies) you give your animal, including the amount and time you give each.
• Tell your veterinarian about any conditions or diseases your animal may have now or has had in the past.
• If your animal has been treated for the same disease or condition in the past, tell your veterinarian aboutthe treatment and how well it did or didn't work.
• If your animal is pregnant or nursing, talk to your veterinarian aboutthe risks of using this drug.
• Tell your veterinarian and pharmacist about any medication side effects (including allergic reactions, lack of appetite, diarrhea, itching, hair loss) your animal has developed in the past.

Side effects that usually are not serious include:

• Sedation (sleepiness, fatigue) is the most common side effect
• Most animals will become tolerant to this effect with time and will not get as sleepy when given the medication
• Excitement
  • Occasionally, hydroxyzine causes some animals to become overly excited.

Uncommon side effects:

• Dogs: Muscle tremors 
• Cats: Greater thirst, behavior changes 
• Lack of appetite, low blood pressure 

You don’t have to be overly concerned if you see any of these unless they are severe, worsen, or continue to be a problem. Contact your veterinarian if this happens.

If you have any other questions or concerns about this medication, contact your veterinarian or pharmacist.

Precautions/Warnings:

Hydroxyzine is contraindicated in patients hypersensitive to it or its active metabolite, cetirizine. Because of its anticholinergic activity, hydroxyzine should be used with caution in patients with prostatic hypertrophy, bladder neck obstruction, severe cardiac failure, angle-closure glaucoma, prolonged QT interval, pulmonary diseases with minimal mucosal secretions, or pyeloduodenal obstruction. Avoid or use with caution in patients with a history of seizures.

Pediatric human patients are more susceptible to the adverse CNS effects of antihistamines; it is recommended to avoid use in neonates.

Hydroxyzine is a vesicant, and IV administration is contraindicated. In humans, hydroxyzine injection may only be administered IM, preferably into a large muscle, as local reactions (including significant tissue damage) may occur after IM administration. Tissue necrosis and abscess have occurred after SC injection.