Clemastine Fumarate for Dogs

Written by: Merliza Cabriles, DVM

Quick links: Dosage CalculatorOverdoseSide Effects


Clemastine Fumarate for DogsClemastine Fumarate is an antihistamine classified under the ethanolamine group. (Some commonly know brand names are: Wal-Hist, Allerhist, Antihist-I , Dayhist, Tavist). It is a H1 Blocker that works by inhibiting the action of histamine on the tissues of the body.

Histamine is the chemical responsible for the distinct symptoms that are manifested when a dog or a cat is suffering from an allergic reaction.

Clemastine Fumarate provides temporary relief from the most common symptoms of allergies, such as:

  • Sneezing
  • Congestion
  • Watery eyes

It also works as an antipruritic to help soothe persistent itching associated with allergic reactions.

If you got here searching for Tavist®, from what we know it’s no longer on market because of medical risks.


Talk to your vet first!

When you are considering the use of Clemastine to manage your pet’s allergies, it is a good idea to consult your veterinarian regarding important concerns and/or questions you may have about the treatment regimen. You can also inquire about tests that may be necessary while your pet is taking Clemastine, as well as viable treatment options that can help manage your pet’s allergy symptoms. Discussing the length of the treatment period and the possible outcome will also give you an idea regarding your pet’s treatment regimen.


Clemastine Fumarate is a commonly prescribed antihistamine for dogs.

While it is registered for exclusive use in humans, many veterinarians prescribe Clemastine for dogs, as an extra label medicine. It is often prescribed with other anti-inflammatory medications, such as Diphenhydramine or Hydroxyzine, to enhance its efficacy. Clemastine is thought to have less of a sedative effect compared to some antihistamines.

A clinical trial on the efficacy of Clemastine in the management of allergic pruritus (itching) in dogs showed elimination of pruritus in 10% of the dogs; and 19% showed marked improvement with some residual pruritus. Side effects were uncommon and adverse reactions were observed in only 4% of the dogs. (William et al, 1993).


Dosage and Dosing Instructions

Clemastine Fumarate is available:

  • As an unflavored 1.34 mg tablet that can be bought over-the-counter.
  • It is also available in 0.1 mg/mL syrup.
  • You will need a veterinary prescription for Clemastine 2.68 mg tablets.


Clemastine dosage for dogs depends on the body weight.

  • Dogs weighing less than 22 lbs (10 kilograms) can be given half of Clemastine1.34 mg tablet every 12 hours;
  • Dogs that weigh between 22-55 lbs (10-25 kilograms) can be given one 1.34 mg tablet every 12 hours;
  • And dogs weighing more than 55 lbs (25 kilograms) can be given 1.5 tablets (1.34 mg) every 12 hours. (Saunders Handbook Of Veterinary Drugs: Small and Large Animal)


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The duration of treatment will depend on the reason for and the animal’s response to the treatment regimen. The dosage instructions issued by the veterinarian should always be followed and the medication should only be administered to the pet for which it was prescribed.

If you miss a dose, make sure to give it once you remember. But if it’s almost close to the schedule of the next dose, just forego giving the missed dose and stick to the regular schedule. Don’t give two doses at a given time!


Clemastine Fumarate Overdose in Dogs

If you know or suspect your pet has had an overdose, make sure to call your veterinarian immediately.

While the drug is known to exhibit fewer side effects than other popular antihistamines (such as Diphenhydramine, Hydroxyzine, or Chlorpheniramine) that are used in pets, overdose may result in the following symptoms:

  • Dry mouth
  • Rapid heart rate
  • Dry mouth
  • Fever
  • Low blood pressure
  • Urinary retention


Common Side Effects of Clemastine in Dogs

This medication can affect:

  • The central nervous system causing sedation or Inconsistent hyperactivity or excitement
  • Dryness of the mouth which may be displayed in your pet as an increase in thirst
  • Diarrhea (most common side effect observed in cats)
  • Rapid heartbeat
  • Difficulty in urinating

If you observe any of these side effects, contact your veterinarian as soon as possible.



Animals with a known hypersensitivity or allergy to Clemastine Fumarate should not take this medication.

Special care is required while administering this medication in animals with the following medical conditions:

  • Known prostate and bladder conditions
  • Heart ailments
  • Obstruction of the urinary bladder
  • Gastro-intestinal obstruction
  • Glaucoma.

EXTREME CIUTION is needed while using this medicine on animals that are on sedatives or tranquilizers.


During Pregnancy

While the drug is presumed to be safe for use in pregnant animals, its traces may be present in the mothers’ milk, so be cautious while using this medication in nursing pets for it may have adverse effects on the young. The drug is contraindicated in animals that will undergo allergic skin testing.


Working Dogs

Do not administer to dogs that are utilized for police and military work, as well as those that are used as guide dogs for hearing and visually-impaired persons. These working dogs require full alertness in their jobs. Clemastine Fumarate may bring about too much sedation that can interfere with the animal’s ability, efficiency and competence.

You should inform your veterinarian if your pet is used for breeding, pregnant, taking other medications or supplements, or has had any adverse reactions to previous medications. Avoid giving new food or medications without first consulting your veterinarian.



Since there is always the possibility of adverse drug interactions, you should consult your veterinarian before using Clemastine with any of the following:

  • Vitamins and supplements
  • Central nervous system (CNS) depressants – barbiturates or antidepressants
  • Monoamine Oxidase Inhibitors (MAOIs), such as furazolidine, selegiline (Anipryl), isoniazid, amitriptyline, phenobarbital, selegiline, or amitraz (an active ingredient in some types of tick collars, and in Mitaban, which is often used for mange treatment)
  • Flea and tick collars



It should be stored in a childproof container that can be tightly closed and is resistant to light. The container should be placed away from heat and direct sunlight. It should be stored at room temperature, in a place that is cool and dry. As with all medications, Clemastine should be kept out of reach of children and pets.

approved by veterinarian




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