Anithistamines for dogs (and cats) Many of us are seeing an increase in allergies in our dogs at this time of year, and more often than not, it’s seasonally related (just like with humans and hay fever). Personally, I always start with Benadryl/Diphenhydramine if one of ours starts itching/nibbling, but my all-time favourite (for me too) is Rx Hydroxyzine. Do bear in mind that not every antihistamine works on every dog, just like with humans – you might need to try different ones to find one that works. And unfortunately, in some cases, you might need to go further, talking with your vet about low-dose steroids or other medications.
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) Clemastine (formerly “Tavist”) – One of the more effective choices. Unfortunately, the over the counter form of Tavist containing the antihistamine “clemastine” has become unavailable. Therefore, we carry this antihistamine in our in-house pharmacy, in the 1.34mg strength. Available in: 1.34mg tablets, 2.68mg tablets, and 0.67mg/5ml liquid
Dosage: DOG WEIGHT (in pounds) Dose (tablet = 1.34mg tablet) 5-15 (liquid) 1-2cc or ¼ tablet twice daily 15-25 ½ tablet twice daily
25-50 1 tablet twice daily 50-70 1 or 2 tablets twice daily
Over 70 2 tablets twice daily
CATS: ¼ to ½ tablet once daily (1.34mg tablets). Very effective in cats May cause: sedation, hyperactivity, or diarrhea (in cats only). Discuss with your veterinarian if your pet has: Prostatic hypertrophy (intact male dogs), urinary or GI obstruction, or severe heart disease NOTE: Do not confuse this product with a similar product called “Tavist N.D,” which is a different type of antihistamine, and is less effective.
2) 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!).
3) 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!).
4) 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.
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