Doxepin

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 (extra label). Many drugs are commonly prescribed for off-label use in veterinary medicine. “Off label” means the drug is being used in a way that has not been reviewed or approved by the U.S. Food and Drug Administration (FDA) or Health Canada. In these instances, follow your veterinarian’s directions and cautions carefully, as they 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.
• Always ensure access to clean water.
• Do not give this medication with aged cheeses or while using certain flea/tick collars.
• Discontinue this medication at least two weeks prior to skin allergy testing.

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

What if I miss giving my pet the medication?

If you miss a dose, give it as soon as you remember, and then continue with the regular dosing schedule. However, if it is almost time for the next dose, skip the missed dose and resume the regular dosing schedule. Do not give the pet two doses at once.

Are there any potential side effects?

Doxepin may cause the following side effects:

• Sleepiness (common)
• Dry mouth
• Straining to urinate
• Decreased appetite
• Vomiting
• Diarrhea
• Constipation

Serious adverse reactions may occur, and are usually associated with high doses. If any of the following signs develop, stop giving doxepin and contact your veterinarian immediately:

• Excitability
• Abnormal heart rhythms
• Collapse
• Coma
• Abnormal bleeding
• Fever
• 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?

DO NOT USE doxepin in:

• Pets that are allergic to it or other tricyclic antidepressants
• Pets that are also using a monoamine oxidase inhibitor (MAOI), including certain flea/tick collars
• Pets undergoing skin allergy testing within two weeks

USE WITH CAUTION in pets that:

• Have heart disease
• Have with glaucoma
• Have dry eye (keratoconjunctivitis sicca/KCS)
• Have  difficulty urinating
• Have prostate enlargement
• Have thyroid disease
• Have adrenal tumors
• Have gastrointestinal blockages
• Have epilepsy (seizures)
• Are very young or very old
• Are pregnant or nursing (consider a milk replacer)

Are there any drug interactions I should be aware of?

Several medications should be used with caution when given with doxepin, including:

• Anticholinergic agents
• Antihistamines
• Drugs that prolong the QTC interval
• MAOIs
• Nonsteroidal anti-inflammatory drugs (NSAIDs)
• Selective serotonin reuptake inhibitors (SSRIs)
• 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 before starting any new treatment.

Is any monitoring needed with this medication?

• Your veterinarian will let you know when and how they want to reassess your pet to ensure the medication is working and not causing side effects.
• At home, monitor for any side effects such as those noted above. If any occur, stop using the medication and contact your veterinarian.

How do I store doxepin?

• Store this medication at room temperature, protected from light.
• Keep the container out of reach of children and pets.

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. Be prepared to provide information about the product and your pet's weight and symptoms.