What Are the Uses of Mirtazapine for Cats?

It is the responsibility of all pet owners to ensure that their pets are getting a healthy, well-balanced meal. But what happens when your pet has a low appetite, refuses to eat, or has a medical condition that causes poor appetite and nausea? 

Mirtazapine is a human drug used as an antidepressant, and it works by increasing the amount of serotonin and noradrenaline (mood-enhancing chemicals) in your brain. In cats, veterinarians commonly use this drug to treat vomiting, loss of appetite, and nausea. It is also used, seldomly, to treat behavioral problems.

How Does Mirtazapine Work?

Neurotransmitters are one part of the Central Nervous system that allow messages from one cell to pass to another. Norepinephrine (NE) is a neurotransmitter that acts to increase appetite at specific receptors. 

Mirtazapine is believed to act as an antagonist (blocks the receptors’ activity) to the receptors that would stop the release of Norepinephrine. This action leads to a subsequent increase in NE and appetite. 

Mirtazapine also blocks specific serotonin receptors, which provide an anti-vomiting and anti-nausea effect. The boost of NE and serotonin usually improves mood, which is why it is also used to treat emotional imbalances.

What Are the Uses of Mirtazapine for Cats?

Your veterinarian may prescribe Mirtazapine for your cat to help counter ailments that cause nausea, weight loss, and poor appetites. These include:

Chronic Renal Failure

Chronic Renal Failure (CRF) affects an estimated 20% of felines above 15 years. Although veterinarians are unsure of the exact cause of this disease, they believe that infections, congenital disabilities, and tumors may be linked to renal failure. 

When ESA cats experience CRF, they cannot effectively filter out waste and toxins, which can lead to the development of electrolyte imbalances, anemia, and other conditions. These conditions can cause weight loss, vomiting, and nausea. Mirtazapine, when administered, reduces these symptoms.

Diabetes Mellitus

Diabetes is an illness in which your body does not produce sufficient insulin to control the amount of glucose in the blood, causing the blood sugar levels to rise. 

This disease affects about 1 in every 400 cats and is initially recognized by an increase in appetite. However, as the disease progresses, the desire to eat drops, and other symptoms, such as vomiting and weight loss, begin to show. 

When other treatment options fail to keep this condition under control, veterinarians typically prescribe Mirtazapine. 

Lethargy, Depression, and Anxiety

Cats sometimes become lethargic, agitated, and depressed because of old age or other health conditions. Mirtazapine is particularly useful for cats experiencing these symptoms.

Veterinarians usually use Mirtazapine because of its effects on brain chemicals, with the anti-nausea and increased appetite seen as added benefits.

Compared to other antidepressant drugs, Mirtazapine has a rapid onset of action. Because of its relaxing effects on felines, vets may prescribe it to your cat occasionally to make them more emotionally comfortable and stable.

What Are the Potential Side Effects of Mirtazapine?

Although cats generally tolerate Mirtazapine well, there are some potential side effects that pet owners should be aware of and monitor. 

The most common side effects of Mirtazapine include the following:

• Increased vocalization in approximately 50% of cats.
• Serotonin syndrome: In cats, this manifests as general hyperactivity.
• About 10% of the cats that use the topical ointment Mirataz will experience skin reactions at the site of application, near the pinna. These reactions can include scabbing, redness, build-up of residue, and crusting.
• Approximately 25 to 33% of cats using this medication experience gastrointestinal side effects such as vomiting and agitation.
• Sedation in cats that receive higher doses since Mirtazapine also acts as a histamine blocker. 
• In cases of overdose, the common symptoms include agitation, vomiting, and vocalization.

Mirtazapine Risk Factors 

Some cautions and concerns regarding using Mirtazapine for your emotional support animal include:

• Mirtazapine has not been proven safe for cats that are pregnant or lactating.
• The effects of the transdermal ointment have not been tested on cats below 4.4 lbs. (2 kilograms) or in cats younger than six months. 
• Mirtazapine should be administered cautiously to cats with low platelets, leukemia, or any blood disease history. For these cases, regular blood test monitoring is also recommended.
• Mirtazapine can increase the values of the liver enzyme tests, although these elevations usually disappear after a month of drug withdrawal.

How to Properly Dose and Administer Mirtazapine for Cats

The dosage for this drug varies depending on the mode of administration. There are two primary ways to administer Mirtazapine to cats:

Tablets

Administration: You can administer Mirtazapine to cats orally in tablet form. You can do this with or without food. If you give the cat the tablet at mealtime, supervise them to ensure they take it. If the tablet orally disintegrates, use completely dry hands to administer it.

Dosage: The recommended starting dose for older cats and cats with liver disease is 1.88mg every 48 hours. The dose for young, healthy cats is 1.88mg every 24 hours.

Tip: Mirtazapine tablets are available in 7.5, 15, 30, and 45 mg, which you must break to the appropriate dose. However, this could lead to administering the wrong dosage. Contact the veterinarian immediately if you notice your cat having any adverse reactions.

Ointment

Administration: Mirataz, a Mirtazapine transdermal ointment, is applied topically to the pinna of the cat’s ear, switching between the right and left ear. The person administering it must wear gloves, and the cat should be isolated from other animals for two hours after application.

Dosage: The product label for this treatment suggests that the recommended dose for a cat is a 1.5-inch ribbon of ointment. This is approximately 2mg.

Tip: It is essential to note that the exact dosage will vary depending on the cat's age, weight, health, and other conditions.

What Should I Do If I Miss My Pet’s Mirtazapine Dose?

If you miss a prescribed dose, give your cat the medication as soon as you remember. 

Afterward, administer the next dose after waiting the recommended time. Only give your cat one dose at a time—with no extras to make up for missed doses—and follow the exact dosing information provided by the vet.

Drug Interactions With Mirtazapine

Although drugs usually don’t interact with Mirtazapine, there are a few exceptions. A cat prescribed amitraz, selegiline, and fluoxetine should not use Mirtazapine. 

While veterinarians will usually check for potential interactions with other drugs before giving a prescription, the pet owner should also keep the vet updated on the drug history of their cat. 

Visit Pettable's page for more information on pet care and treatment, getting an ESA letter, and other resources.