By Rania Gollakner, BS, DVM, MPH

What is doxepin?

Doxepin (brand names: Sinequan®, Silenor®, Prudoxin®, Doxepine®, Adapin®, Anten®, Aponal®, Deptran®, Desidoxepin®, Doneurin®, Doxal®, Doxepia®, Gilex®, Mareen®, Quitaxon®, Triadapin®, Xepin®, Zonalon®) is a tricyclic antidepressant and antihistamine used to treat psychogenic dermatoses, especially those with an anxiety component. Examples of these conditions include tail biting, anal licking, excessive grooming, psychogenic alopecia, and feather plucking.

Its use in cats, dogs, horses, and birds to treat psychogenic dermatoses and allergies is ‘off label’ or ‘extra label’. Many drugs are commonly prescribed for off label use in veterinary medicine. In these instances, follow your veterinarian’s directions and cautions very carefully as their directions may be significantly different from those on the label.

How is doxepin given?

Doxepin is given by mouth in the form of a tablet, capsule, or oral liquid. It may be given with or without food; however, if vomiting occurs when dosed on an empty stomach, give future doses with food. Ensure access to clean water at all times. Do not give this medication with aged cheeses or while using certain flea/tick collars.

This medication can take a few weeks before full effects are noted, but side effects can occur immediately. Gradual improvements are usually appreciable after a few days.

What if I miss giving my pet the medication?

If you miss a dose, give it when you remember and then wait the recommended amount of time between doses. Alternatively, you may skip the dose you missed and give it at the next scheduled time, and then return to the regular dosing schedule. Never give your pet two doses at once or give extra doses.

Are there any potential side effects?

The most common side effect is sleepiness. Other side effects that are less common include dry mouth, straining to urinate, decreased appetite, vomiting, diarrhea, and constipation.

Serious side effects, usually associated with high doses, include excitability, abnormal heart rhythms, collapse, coma, abnormal bleeding, fever, and seizures.

This moderate-acting medication should stop working in a few days, although effects can be longer in pets with liver or kidney disease.

Are there any risk factors for this medication?

Doxepin should not be used in pets that are allergic to it or other tricyclic antidepressants. Doxepin should not be used in conjunction with a monoamine oxidase inhibitor (MAOI); including certain flea/tick collars, or in pets undergoing skin allergy testing within two weeks. It should be used cautiously in pets with heart disease, glaucoma, dry eye (keratoconjunctivitis sicca/KCS), difficulty urinating, prostate enlargement, thyroid disease, adrenal tumors, gastrointestinal blockages, or epilepsy (seizures). Doxepin should also be used cautiously in very young, very old, pregnant or nursing pets. If used in a nursing pet, consider a milk replacer.

Are there any drug interactions I should be aware of?

The following medications should be used with caution when given with doxepin: anticholinergic agents, antihistamines, cimetidine, dextromethorphan, drugs that prolong the QTC interval, meperidine, MAOIs, nonsteroidal anti-inflammatory drugs (NSAIDs), pentazocine, quinidine, selective serotonin reuptake inhibitors (SSRIs), sympathomimetic agents, or tramadol.

This medication may also interact with blood glucose levels and with intradermal allergy testing; discontinue this medication at least two weeks prior to skin allergy testing.

Be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking.

Is there any monitoring that needs to be done with this medication?

There is no specific monitoring that needs to be done while your pet is taking this medication. Your veterinarian may monitor your pet to be sure that the medication is working. Monitor for serious side effects.

How do I store doxepin?

Store this medication at room temperature, protected from light.

What should I do in case of emergency?

If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility.

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