Mirtazapine for Dogs Appetite, Liver Disease, Kidney Failure and Cancer: Dosage, Side-Effects, Safety

Mirtazapine for Dogs

If you search Google for “what stimulates hunger in a dog?” you may come across the term mirtazapine. Also known as Remeron®, mirtazapine is a prescription antidepressant drug from a class referred to as tricyclic anti-depressants. Although it was originally intended for human use, it has been found useful for dogs and cats with appetite loss and behavioral problems. This article explores more on using mirtazapine for dogs conditions.

How Mirtazapine Works For Dogs

Now that you know that you can indeed use mirtazapine for dogs’ problems, you may want to know how the drug works.

Mirtazapine works by raising the levels of serotonin and other neurotransmitters in a pet’s brain. It targets the serotonin receptors in your dog’s gastrointestinal tract and brain. The former receptors help to reduce nausea and vomiting while the latter helps to stimulate appetite.

Although the Food and Drug Administration (FDA) does not approve the veterinary use of mirtazapine, veterinarians can legally prescribe it as an extra-label drug.

As a prescription drug, though, Mirtazapine is not available over the counter. Your veterinarian may have it in their clinic, but to obtain it from a pharmacy (drugstore), you must have a prescription from the veterinarian.

Uses of Mirtazapine for Dogs

Mirtazapine is sometimes used to treat depression and separation anxiety. Some veterinarians also use mirtazapine for behavior modifications e.g. inappropriate urination.

Mirtazapine is however used for appetite stimulation in the majority of the cases. It is mainly used in cases where nausea and poor appetite occur as symptoms of a disease.

The drug is in particular very helpful for pets that are suffering from liver disease, renal (kidney) failure, stomach or intestinal disease, or any other condition that makes the pet in question feel nauseated, and thus lose their appetite.

Mirtazapine for Dogs Cancer

Mirtazapine also has mild antihistaminic properties. While you are unlikely to have your vet prescribe the drug for the purpose given the ready availability of antihistamine drugs, this may offer additional benefits to dogs with cancer. It is in fact not uncommon for vets to give mirtazapine to pets undergoing chemotherapy.

This helps to curb the vomiting and nausea typical to chemotherapy drugs as well as stimulates a dog’s appetite, thus preventing weight loss.

Dogs with from mast cell tumors, in particular, tend to excessive histamine. This often manifests itself in (inflammation) swelling, redness, discomfort, loss of appetite, vomiting, and in some case low blood pressure. Used alongside the cancer treatment opted for, mirtazapine makes a particularly good choice for the alleviation of these symptoms of mast cell tumors.

As for how to use mirtazapine for dogs’ appetite stimulation and other purposes, it is always given orally. The drug is typically sold in the form of film-coated tablets.

Mirtazapine dosage for dogs

When using mirtazapine for dogs’ appetite loss and other conditions, it is important to only give it once a day. Otherwise, your dog may be at risk of serotonin syndrome and related complications. A daily dose of 3.75 – 30 mg is usually given depending on the dog’s weight. Here is a breakdown of the recommended dosage for mirtazapine in dogs:

  • For dogs weighing less than 20 pounds: Give 3.75 mg of mirtazapine once per day.
  • If the pooch weighs 21 – 50 pounds: Give 7.5 mg once per day.
  • Dogs weighing 50 – 75 pounds: Give 15 mg once per day.
  • Dogs weighing more than 75 pounds: Give 30 mg once per day.

For dogs with kidney failure or liver disease, the dosage is usually adjusted to reflect a 30 percent reduction. For example, a dog with kidney or liver disease and weighing 21-50 pounds should take 5.25 mg instead of 7.5 mg of mirtazapine.

Duration of Use

How long should this dosage of mirtazapine for dogs continue? That depends on the exact condition requiring treatment, your dog’s response to the medication, and whether or not there are any known adverse effects. Your veterinarian will advise accordingly. Ensure though that your pooch continues with the medications as directed all the way to the end.

It is important also that you don’t exceed the dose given. When given in an overdose, mirtazapine can cause heart problems. In fact, it is potentially fatal if ingested in very large doses. If you experience a case of overdose with mirtazapine, take your dog to the veterinarian right away.

You also need to be aware of possible adverse drug interactions while using any drugs. Mirtazapine should not be used alongside any other medication that is known to increase serotonin levels, says Dr. Demian Dressler, a veterinarian based in Hawaii.

If your dog is on medications such as Prozac (also known as fluoxetine), Elavil (amitriptyline), or Anipryl (selegiline), inform your veterinarian.

As a matter of fact, it is always prudent to let your vet know of any medications that you may be giving to your dog.

Mirtazapine Side Effects in Dogs

Although drowsiness is the side effect most commonly observed in pets, it is usually not serious. The most significant concern in as far as side effects of using mirtazapine for dogs’ appetite stimulation and other purposes is a condition known as serotonin syndrome. This is hardly surprising given the fact that works by increasing the level of serotonin in the brain.

Serotonin Syndrome in Dogs

Serotonin syndrome is a rare condition in dogs whereby there are higher than normal levels of serotonin in the brain. This usually happens when mirtazapine is administered in conjunction with other medications with a similar effect.

Serotonin reuptake inhibitors or SSRIs, such as Prozac (fluoxetine) are good examples. Dr. Dressler also adds Elavil (amitriptyline) and Anipryl (selegiline) to that list. You should as well avoid concurrent use of mirtazapine with tramadol. This raises the risk of serotonin syndrome significantly, says the Mar Vista Animal Medical Center.

Serotonin syndrome is characterized by signs and symptoms such as:

  • Dilated pupils
  • Faster heart rate
  • A rise in body temperature
  • Shivering
  • Difficulty breathing
  • Elevated blood pressure
  • Hyperactivity

If you notice any of these signs and symptoms of serotonin syndrome after putting your pooch on the drug, call your vet urgently. According to Mar Vista Animal Medical Center, Cyproheptadine, a medication that is often used as an appetite stimulant for cats, can be administered as an antidote when serotonin syndrome occurs.

Other Side-Effects of Using Mirtazapine for Dogs

According to the Mar Vista Animal Medical Center, a few cases have been documented where mirtazapine causes “abnormalities in blood cell lines developing in the bone marrow”. For this reasons, your veterinarian needs to check dogs with a history of blood-related diseases and conditions such as low platelets and leukemia very closely while on the drug. This involves taking regular blood tests.

Although there is not enough evidence at the moment, mirtazapine may not be suitable for pregnant and lactating (breastfeeding) pooches.

To avoid any adverse side effects while using mirtazapine for dogs appetite loss, nausea (and vomiting), or any other purpose, follow the veterinarian’s instructions to the letter. Also, inform them of any medication that your pet furry friend may be taking.


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