Clemastine
(klem-as-teen)
Description: Antihistamine
Other Names for this Medication: Tavist®, Dayhist-1®, Tavegil®
Common Dosage Forms: Veterinary: None. Human: 1.34 mg & 2.68 mg tablets

Key Information: Use only products that contain clemastine as a single active ingredient. Any other ingredients (eg, pain relievers, decongestants) found in human-label combination products can be toxic to animals. Antihistamines should be used on a regular, ongoing basis in animals that respond to them. They work better if used before exposure to an allergen (eg, pollens). May be given with or without food. If your pet vomits or acts sick after receiving the medication on an empty stomach, try giving the next dose with food or a small treat. If vomiting continues, contact your veterinarian. May cause sleepiness; this effect may lessen with time. Cats can develop diarrhea when taking this medicine.

How is this medication useful? Allergies cause histamine release, which causes itchy skin. Clemastine blocks histamine’s effects and reduces itchiness associated with allergies. It can also be used as an additional treatment for itching related to certain types of cancers (eg, mast cell tumors). As with
other antihistamines, the response to this drug can vary between animals and is unpredictable, so your veterinarian may try several different antihistamines to see which one works best for your animal. Clemastine 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.

How long until I will know if this medication is working, and how long will the effects of this medication last? This medication should help your animal feel better within 1 to 2 hours. Your animal’s clinical signs should improve after that time. The effects of this medication are short-lived, meaning they will stop working within 24 hours, although the benefits may be prolonged if your animal has decreased kidney and/or liver function.

What are the side effects of this medication? Common but not serious side effects include: The most common side effect, which is often desirable, is sleepiness. Most animals will become tolerant to this effect with time and will not get as sleepy when given the medication. Sometimes animals may become overly excited while taking this drug. Dry mouth and trouble urinating (eg, straining) are possible but not common. Infrequently, clemastine may cause gastrointestinal distress such as vomiting, decreased appetite, and diarrhea (in cats in particular). You don’t have to be overly concerned if you see any of these signs unless they are severe, worsen, or continue to be a problem. Contact your veterinarian if you have any concerns.

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