Mirtazapine for Cats - Dosage and Side Effects

Mirtazapine is the active ingredient in certain antidepressant drugs. However, in cats it is used as an appetite stimulant. This action works as it produces an increase in the concentration of norepinephrine (norepinephrine) in the blood serum. Norepinephrine is a compound that can function as a neurotransmitter when it is released by neurons of the sympathetic nervous system and increases the rate of heart contractions.

It is also a stress hormone when. Along with adrenaline, it is responsible for activating and alerting the body to enter ‘fight or flight’ mode. When this happens, their heart rate increases, glucose is released, blood flows to the muscles and the oxygen supply to the brain increases.

The drug mirtazapine has a tetracyclic structure. It is an antidepressant that promotes the release of norepinephrine and epinephrine because it blocks presynaptic α-2 receptors. It also has an action against serotonin, since it acts by antagonizing the 5-HT2 and 5 receptors -HT3 of it. Serotonin is a compound that has functions on emotions, mood, digestion and appetite.

It also has antihistamine activities by blocking H1 receptors that can cause sedative effects. Cats treated with mirtazapine may also gain weight because this drug causes changes in tumor necrosis factor (TNF) and leptin. For this reason, we need to reduce potential feline obesity problems.

Mirtazapine offers several therapeutic uses in cats. Commonly, it is used for the following purposes:

• Treatment of anorexia: certain chronic diseases in cats such as liver disease, feline triaditis, chronic kidney disease, intestinal diseases and tumors can lead to loss or reduction of appetite. Chemotherapy treatments for neoplasms and infectious diseases can cause anorexia, especially those that affect the upper respiratory tract (e.g. feline rhinotracheitis, feline calicivirus or bacterial infections). The increase in norepinephrine produced by mirtazapine stimulates the appetite of cats affected by these diseases.
  
  
• Treatment of nausea: it can control nausea by acting on the gastric and intestinal neuroreceptors that are connected to the vomiting center of the brain, which is responsible for nausea.
  
  
• Weight loss treatment: due to its action on leptin and TNF, it can stimulate weight gain in cats. This is secondary to the stimulation of appetite and control of nausea.
  
  
• Treatment of behavioral problems: the use of mirtazapine has been studied in cats with anxiety, stress, compulsive disorders and phobias. In these cases, the results obtained are promising. Additionally, due to the appetite stimulation effect, it can be especially useful in cats that stop eating due to stress.

Take a look at our article on how to calm down a stressed cat to learn more about feline anxiety.

Mirtazapine in cats is used at doses of 1.88 or 3.75 mg every 24/48 hours. It is taken orally as an appetite stimulant and to control nausea. Generally, the lowest dose of 1.88 mg is used because it has lesser risk of adverse effects.

Recently, a new preparation has been released for cats weighing between 2 and 7 kg. It is in topical format for application through the skin of the inner surface of the ear. The required dose of mirtazapine in cats by this route is 2 mg of mirtazapine. To achieve this dose, an amount of 0.1 g of ointment should be applied, which is equivalent to a 3.8 cm line, once a day for 14 days.

Mirtazapine tablets should not be used in the following cases:

• Cats with heart disease.
• Cats with blood pressure problems.
• Cats with alterations in white, red blood cells or platelets.
• Use with caution in pregnant or lactating cats.

In topical form, mirtazapine should not be used in the following cases:

• Cats weighing less than 2.1 kg or more than 7.0 kg because their efficacy and safety have not been studied.
• Cats in heat, pregnant cats or lactating cats.
• Kittens less than 7.5 months of age.
• Cats treated with other drugs such as monoamine oxidase inhibitors (MAOIs), cyproheptadine or tramadol.
• It has not been studied in cats with certain such as very advanced kidney disease.

The side effects that oral mirtazapine therapy in cats can produce the following problems:

• Changes in behavior
• Low blood pressure
• Agitation
• Sedation
• Increased liver enzymes
• Tachycardia
• Vocalization
• Salivation
• Tremors

On the other hand, the side effects of the topical mirtazapine application include the following:

• Skin problems (dry skin, flaking, redness, etc.) at site of application
• Lethargy
• Hyperactivity
• Ataxia
• Increased attention seeking
• Aggressiveness
• Polyuria (increased urination)
• Dehydration
• Vomiting

If you want to know about other medications for cats and their administration, take al look at our articles on ivermectin for cats and prednisone for cats.

This article is purely informative. AnimalWised does not have the authority to prescribe any veterinary treatment or create a diagnosis. We invite you to take your pet to the veterinarian if they are suffering from any condition or pain.

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