Doxepin (Sinequan® or Silenor®) for Dogs and Cats

Overview of Doxepin for Dogs and Cats

Doxepin, commonly known as the prescription drugs Sinequan® and Silenor®, is used to treat dogs for depression, noise phobia, and anxiety-related disorders, such as canine obsessive-compulsive disorders, especially acral lick dermatitis.
Behavioral disorders in dogs and cats are a common reason for veterinary visits. Unacceptable or dangerous animal behavior problems are also sometimes cited as a justification for euthanasia.
Veterinarians have placed greater emphasis on training and behavior, and specialists working in the field of animal behavior have increasingly adopted drugs used in human behavioral medicine for animal use. Doxepin is one of these drugs.
Doxepin is a human antidepressant that has found some application in the treatment of veterinary behavior problems. The drug blocks dopamine receptors in the central nervous system. Doxepin is also a very potent antihistamine (H1 and H2 blocker) 700 times more potent than diphenhydramine (Benadryl) and 50 times more potent than hydroxyzine (Atarax) in that respect.
Doxepin is a prescription drug and can only be obtained from a veterinarian or by prescription from a veterinarian.
This drug is not approved for use in animals by the Food and Drug Administration (FDA) but may be prescribed legally by veterinarians as an extra-label drug.

This drug is registered for use in humans only.
Human formulations: Sinequan® (Pfizer), Silenor® and various generic preparations
Veterinary formulations: None

Doxepin is used to treat depression, noise phobia, and anxiety-related disorders, such as canine obsessive-compulsive disorders, especially acral lick dermatitis.

While generally safe and effective when prescribed by a veterinarian, doxepin may cause unacceptable side effects in some animals.
Doxepin should not be used in animals with known hypersensitivity or allergy to the drug.
Doxepin should not be used in animals with glaucoma or those with medical problems that are associated with urinary retention.
Doxepin should be used with caution in seizure-prone animals.
Side effects include: low blood pressure, high blood pressure, rapid heart rate, constipation, and dry mouth.
Doxepin sometimes turns urine blue-green in color.
Doxepin may interact with some other medications. Consult your veterinarian to determine if other medications that your pet is receiving might adversely interact with doxepin. Such drugs include: monoamine oxidase inhibitors, thyroid medications, atropine, sedatives, antihistamines, norepinephrine, and phenytoin.
The following drugs may increase the effects of doxepin: cimetidine (Tagamet), estrogens, fluoxetine (Prozac), some sedatives, enalapril, verapamil, and ranitidine (Zantac).

Doxepin is available as 10 mg, 25 mg, 50 mg, 75 mg, 100 mg, and 150 mg capsules.
Doxepin is available in tablets in the 3 mg and 6 mg sizes (Silenor)
Doxepin is also available as a 10 mg/mL oral concentrate.

Medication should never be administered without first consulting your veterinarian.
In dogs, doxepin is dosed at 0.25 to 0.5 mg per pound (0.5 to 1 mg/kg) orally every 12 hours or 1.5 to 2.5 mg per pound (3 to 5 mg/kg) orally every 8 to 12 hours.
To date, no dose for doxepin has been established for cats.
The duration of administration of doxepin depends on the condition being treated, response to the medication, and the development of any adverse effects. Be certain to complete the prescription unless otherwise directed by your veterinarian.