• The following is a list of options for antihistamines that are known to be effective in dogs & cats. The name of the active ingredient is listed, with the name of a well known brand in parentheses. Also listed are approximate doses for different weights, and any precautions.

    CAUTION: Do not purchase antihistamines that are combination products (multi-symptom, cold/flu medicines, decongestants, etc.), especially products that contain decongestants (often labeled with a D, as in “Zyrtec-D”). These products often contain a high level of stimulants that are toxic, even life-threatening, to animals. In addition, products containing acetaminophen (active ingredient in Tylenol) are deadly for cats.

    ANTIHISTAMINES AVAILABLE “OVER-THE-COUNTER”

    1) Diphenhydramine (“Benadryl”)

    Available in: 12.5mg children’s tablets, 25mg capsules, and 12.5mg/5ml liquid (liquid not recommended if it contains alcohol)

    Dosage:

    DOG WEIGHT (in pounds) Dose (tablet = 12.5mg, capsule = 25mg)

    5-10 ½ children’s tablet twice daily

    10-15 1 children’s tablet 2-3 times daily

    15-35 1 capsule 2-3 times daily

    35-50 1 or 2 capsules 2-3 times daily

    50-80 2 or 3 capsules 2-3 times daily

    Over 80 3 or 4 capsules 2-3 times daily

    CATS: Generally not recommended. Clemastine, Chlorpheniramine and Cyproheptadine are more effective.

    May cause: sedation, hyperactivity, diarrhea (rare), vomiting (rare), or loss of appetite (rare).

    Discuss with your veterinarian if your pet has: glaucoma, GI or urinary obstruction, COPD (chronic lung disease), hyperthyroidism, seizure disorders, heart disease or high blood pressure.

    NOTE: Do not use Diphenhydramine products that contain any other active ingredients (like acetaminophen). These other products are potentially toxic to your pet (especially cats!).

    2) Chlorpheniramine (“Chlor Trimeton”)

    Available in: 4mg tablets , and 2mg/5ml liquid

    Dosage:

    DOG WEIGHT (in pounds) Dose (based on 4mg tablet )

    5-10 1/4-1/2 tablet 2-3 times daily

    10-20 1/2 to 1 tablet 2-3 times daily

    20-40 1 to 2 tablets 2-3 times daily

    40-60 2 to 4 tablets 2-3 times daily

    Over 60 4 to 6 tablets 2-3 times daily

    CATS: 1-4 mg per cat once or twice daily. Very effective in cats.

    May cause: sedation or hyperactivity.

    Discuss with your veterinarian if your pet has: glaucoma, high blood pressure, GI or urinary obstruction, hyperthyroidism, heart disease.

    NOTE: Do not use chlorpheniramine products that contain any other active ingredients (like acetaminophen). These other products are potentially toxic to your pet (especially cats!).

    3) Cetirazine (Zyrtec)

    This may be the best antihistamine for eosinophillic inflammation (one of the primary cell types associated with allergies). It is a formerly prescription-only medication that is now available over the counter.

    Available in: 5mg and 10mg tablets

    Dosage:

    DOG WEIGHT (in pounds) Dose

    Less than 15 One 5mg tablet once daily

    15-39 5mg twice daily, or 10mg once daily

    Over 40 10mg twice daily

    CATS: 5mg ½ to 1 tablet 1 or 2 times daily.

    May cause: Hyperexcitability in dogs

    NOTE: Twice daily dosing is often needed.

    ANTIHISTAMINES BY PRESCRIPTION ONLY

    1) Hydroxyzine (Atarax)

    This is one of the more effective antihistamines for dogs. However, it is generally more expensive that the “over-the –counter” antihistamines. We can provide a written prescription for you, if you want to try this antihistamine.

    Available in: 10mg, 25mg, and 50mg tablets

    Dosage:

    DOG WEIGHT (in pounds) Dose

    5-10 One10mg tablet 2-3 times daily

    10-15 1 or 2 10mg tablets 2-3 times daily

    15-30 One 25mg tablet 2-3 times daily

    30-50 One 50mg tablet 2-3 times daily

    50-70 1 or 2 50mg tablets 2-3 times daily

    Over 70 2 or 3 50mg tablets 2-3 times daily

    CATS: ½ to 1 10mg tablet 2-3 times daily.

    May cause: sedation most likely. Dogs rarely: tremors, seizures. Cats: increased thirst, depression or behavioral changes.

    Discuss with your veterinarian if your pet has: prostatic hypertrophy (intact male dogs), urinary or GI obstruction, severe heart disease, or glaucoma.

    NOTE: Also has anti-nausea effect, and can be used for motion sickness.

    2) Cyproheptadine (Periactin)

    This is one of the more effective antihistamines for cats. We carry this medication in stock at our hospital.

    Available in: 2mg and 4mg tablets (we only keep 4mg tablets in stock)

    Dosage:

    DOG WEIGHT (in pounds) Dose (4mg tablet)

    5-10 ¼ tablet 2-3 times daily

    10-20 ½ tablet 2-3 times daily

    20-40 ½ to 1 tablet 2-3 times daily

    40-70 1 to 2 tablets 2-3 times daily

    Over 70 2 or 3 tablets 2-3 times daily

    CATS: 4 mg tablet ¼ to 1 tablet 2 times daily.

    May cause: sedation, dry mouth, Cats: hyperexcitability

    Discuss with your veterinarian if your pet has: urinary or GI obstruction, heart disease, or glaucoma.

    NOTE: Also has an appetite-stimulating effect in cats. Be cautious of excessive weight gain.