Antihistamine & Decongestant Poisoning in Dogs and Cats
Veterinary & Aquatic Services Department, Drs. Foster & Smith

Antihistamines and decongestants.

Diphenhydramine, (Benadryl, Sominex, Nytol, Sleep-Eze, various cough preparations), clemastine (Tavist), brompheniramine and chlorpheniramine (Chlor-Trimeton and various cough preparations), dimenhydrinate (Dramamine), meclizine (Bonine), cyclizine (Marezine), terfenadine (Seldane), hydroxyzine (Atarax, Vistaril), and loratidine (Claritin).

General Information
Histamines are released by body tissues during an allergic reaction and if injuries to certain cells during infections. Antihistamines block the attachment of histamine to cells and help to reduce the effects of histamine.

Toxic Dose
Varies depending upon the product.

Common signs may range from depression with respiratory problems to hyperexcitability with muscle tremors, seizures, and hyperactivity. Vomiting, dilated pupils, increased body temperature, disorientation, heart rhythm abnormalities, and increased or decreased heart rate may be seen.

Immediate Action
Induce vomiting if patient is alert. Seek veterinary attention.

Veterinary Care
General treatment: The induction of vomiting may be continued, gastric lavage is performed, and activated charcoal is administered.

Supportive treatment: Medications are administered to control seizures and heart rhythm abnormalities. Hyperthermia, if present, is treated. IV fluids are administered. Antihistamines are excreted through the kidneys so good urine production is necessary.

Specific treatment: Unavailable.


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Keep this and all other medications out of the reach of children and pets.

If you think your pet has been poisoned...

Contact your veterinarian or one of the Animal Poison Hotlines (listed below) if you think your pet may have accidentally received or been given an overdose of the medication.

**ASPCA Animal Poison Control Center - 24-hour service available throughout North America.

1-888-4ANI-HELP (1-888-426-4435). $65.00 per case, billed to caller's credit card.

Follow-up calls can be made for no additional charge by dialing 888-299-2973.

There is no charge when the call involves a product covered by the Animal Product Safety Service.

**Pet Poison Helpline - 24-hour service available throughout North America for pet owners and veterinary professionals who require assistance with treating a potentially poisoned pet.

1-800-213-6680 ($59.00 per incident). Staffed 24-hours a day.

Updated 6/20/17

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