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Mertazapine (Remeron®)

By: Petplace Veterinarians

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  • Anorexia and behavioral disorders in dogs and cats are frequently the cause for veterinary visits.
  • Behavioral problems that involve unacceptable or dangerous behavior are also a common reason for euthanasia. Veterinarians are placing increasing emphasis on training and behavior, and animal behavior specialists have adopted drugs used in modifying human behavior for use in pets. Mertazapine is one of these drugs.
  • Mertazapine belongs to a class of drugs known as tricyclic anti-depressants. In people, mertazapine is used to treat depression and anxiety.
  • This drug increases the levels of serotonin and other neurotransmitters in the brain.
  • Mertazapine affects serotonin receptors in the gastrointestinal tract that reduce nausea and vomiting. In the brain, these receptors stimulate appetite as well.
  • Mertazapine is a prescription drug and can only be obtained from a veterinarian or by prescription from a veterinarian.
  • This drug is not approved for use in animals by the Food and Drug Administration but can be prescribed legally by veterinarians as an extra-labeldrug.

    Brand Names and Other Names

  • This drug is registered for use in humans only.
  • Human formulations: Remeron® and other equivalents
  • Veterinary formulations: None

    Uses of Mertazapine

  • Mertazapine is used in behavior modification in dogs and cats on occasion but has more used more often as an appetite stimulant in pets that are reluctant to eat. It is commonly used in for long term control of diseases like Inflammatory Bowel Disease in Dogs (IBD) and in elderly renal failure cats.
  • Some veterinrians may also use it for the treatment of separation anxiety in dogs, inappropriate urination (urine spraying) and anxiety in cats.
  • The use of this drug in cats with interstitial cystitis is based on the condition's association with stress, and increased central nervous system activity occurring as a result of this disorder (because of frequent and painful urination).

    Precautions and Side Effects

  • While generally safe and effective when prescribed by a veterinarian, mertazapine may cause side effects in some animals.
  • Mertazapine should not be used in animals with known hypersensitivity or allergy to the drug.
  • Mertazapine may interact with other medications. Consult with your veterinarian to determine if other drugs your pet is receiving could interact with amitriptyline. Such drugs include cimetidine, drugs classified as monoamine oxidase inhibitors, or drugs classified as serotonin reuptake inhibitors (Prozac®-like drugs).
  • Mertazapine has many side effects caused by actions on other body systems. It also acts as an antihistamine, blocks the parasympathetic nervous system and blocks other nervous system effects. Consequences of these effects include sedation, dry mouth, increased water consumption, rapid heart rate, and urine retention.
  • Mertazapine, when accidentally ingested in a large overdose, can have very serious effects on the heart. Pets that consume large amounts of this medication (for example several tablets) should be taken to a veterinarian quickly. Failure to provide prompt medical attention in the instance of an overdose can be fatal.

    How Mertazapine Is Supplied

  • Mertazapine is available in 15 mg, 30 mg, and 45 mg

    Dosing Information

  • Medication should never be administered without first consulting your veterinarian.
  • For dogs, the dose is give once a day and in cats once every 72 hours. The lowest possible dose is used – especially in cats to prevent side effects and toxicity.
  • Mirtazapine is dosed at 3.75 to 30 mg per dog once daily depending on weight of the dog. For example:
    - Dogs less than 20 pounds = 3.75 mg once a day
    - Dogs approximately 21 - 50 pounds = 7.5 mg once a day
    - Dogs approximately 50 - 75 pounds = 15 mg once a day
    - Dogs greater than 75 pounds = 30 mg once a day
  • For cats – 1.875 mg to 3.75 mg is most often used (which is 1/8 to 1/4 for a 15 mg tablet) every 72 hours. For cats less than 15 pounds – 1/8 of a 15 mg tablet (1.875 mg) is used most commonly. Larger cats may get ¼ of a 15 mg tablet = 3.75 mg.
  • The duration of administration depends on the condition being treated, response to the medication and the development of any adverse effects. Be certain to complete the prescription unless specifically directed by your veterinarian. Even if your pet appears better, the entire treatment plan should be completed to prevent relapse or prevent the development of resistance.

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