General Description: Methimazole is an inexpensive drug used in cats to treat an overactive thyroid gland (hyperthyroidism). Your cat’s abnormal appetite, weight loss and heart issues will go back to normal once the thyroid hormone levels are restored. It is also given as a kidney protectant to dogs receiving cisplatin chemotherapy. It is available in 5 mg scored tablets.

What is this drug?

A drug which blocks the production of thyroid hormones
Given by mouth
Reasons for prescribing:

To control hyperthyroidism in the cat
To protect the kidneys in dogs receiving cisplatin chemotherapy
What dogs/cats should not take this medication?

Use with extreme caution in pets with anemia, clotting disorders, bleeding, low white cell and platelet counts, kidney, liver or immune system diseases
Use with extreme caution in pregnant or nursing pets. The young should be placed on milk replacer after they’ve nursed colostrum (first milk immediately after birth)
If your pet has had an allergic reaction to methimazole or like products

Read and follow the label carefully. Ideally, give the medication at the same time(s) daily.

Give the exact amount prescribed and only as often as directed. It is usually givenone to three times a day . If your cat will not take tablets, methimazole can be formulated as a flavored liquid to be mixed in the food, or it can be compounded as a gel to be applied on the hairless skin of the inside of your cat’s ear.

Cats: As this drug is not a cure, but is used to control hyperthyroidism, it is usually given for the remainder of the cat’s life.

Before starting therapy, baseline blood work should be performed to assess thyroid levels and your pet’s overall health. Periodic blood work will be necessary to monitor thyroid levels and the drug’s effect on your pet’s health. Dose adjustments will be made based upon these results and an assessment of how your cat is responding clinically.

Transdermal gel: Wear gloves and wash your hands after handling.

Call ahead for refills.

What if a dose is missed?

If a dose is missed, give it as soon as you can. If it is time already for the next dose, skip the missed dose and go back to the normal schedule. Do not give two doses at the same time.

What to tell/ask veterinarian before giving medication?

Talk to your veterinarian about:

When will your pet need to be rechecked
What tests may need to be performed prior to and during treatment with this drug
What are the risks and benefits of using this drug
Tell your veterinarian about:

If your pet has experienced side-effects on other drugs/products
If your pet has experienced digestive upset now or ever
If your pet has experienced liver or kidney disease now or ever
If your pet has experienced any other medical problems or allergies now or ever
All medicines and supplements that you are giving your pet or plan to give your pet, including those you can get without a prescription. Your veterinarian may want to check that all of your pet’s medicines can be given together.
If your pet is pregnant or nursing or if you plan to breed your pet
Storage and Warnings:

Store in a tight, light resistant, childproof container in a cool, dry place at room temperature away from heat and direct sunlight.

Refrigerate oral suspension.

Keep this and all medication out of reach of children and pets. Owners with low thyroid function should be cautious when handling and should avoid all skin contact.

Call your physician immediately if you accidentally take this product.

Potential side effects:

Any side effects usually occur within the first three months. Side effects may be reduced by beginning at a smaller dose and working up to a full therapeutic dose within a few months. If you notice any of the effects mentioned below, notify your veterinarian.
Decreased appetite, vomiting and lethargy. You may notice these within the first weeks of treatment.
Liver problems (including the above symptoms, plus dark urine, yellowing of the gums, skin or eyes), facial itching resulting in scratching or bleeding tendencies
Underlying kidney disease may become apparent
Rare cases of myasthenia gravis (severely weakened muscles, difficulty swallowing)
Unusually tired, fever (temperature over 103ºF), bruising or bleeding
If you notice any of these symptoms or anything else unusual, contact your veterinarian
Can this drug be given with other drugs?

Yes, but possible interactions may occur with amitriptyline, beta-blockers, clomipramine, cyclophosphamide, digoxin, metoprolol, modified live vaccines, omeprazole, propanolol, theophylline and warfarin
If your pet experiences any unusual reactions when taking multiple medications, contact your veterinarian.

Contact your veterinarian immediately if pet receives more than the prescribed amount.

What else should I know?

Notify your veterinarian if your animal’s condition does not improve or worsens despite this treatment.

As with all prescribed medicines, methimazole should only be given to the pet for which it was prescribed. It should be given only for the condition for which it was prescribed.

This is just a summary of information about methimazole. If you have any questions or concerns about methimazole or the condition it was prescribed for, contact your veterinarian.

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