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Methimazole Allergy in Cats
What is Methimazole Allergy?
Because of the seriousness of the disease (hyperthyroidism), the side effects of the drug (methimazole) have to be weighed against the benefits. Sometimes the side effects will dissipate within a few weeks or can be treated with a different medication to lessen the effects. However, if your cat has any serious side effects that have to do with the liver such as yellow gums, skin, and eyes, vomiting, lethargy, skin lesions, and swollen lymph nodes an evaluation of the use of this medication must be done. It is important that your veterinarian do a blood test to determine the lowest amount of methimazole possible before starting the medication. In addition, blood tests to keep track of liver and kidney enzymes, thyroid hormones, and other abnormalities should be done on a regular basis.
Methimazole is a drug prescribed to treat hyperthyroidism in cats that subdues the processing of thyroid hormones. It is not specifically regulated for animal use but has been accepted for veterinary use by the FDA. This drug should only be used for a short time in cats because of the risk of serious allergy symptoms such as swelling of the face, scratching, and hives, which can lead to seizures, shock, and even coma. Other complications include appetite loss, vomiting, weakness, and liver damage. Some of the less common side effects include anemia, lymph node swelling, abnormal bleeding, and jaundice. If your cat has any of these symptoms when taking methimazole, you need to see your veterinarian right away.
Symptoms of Methimazole Allergy in Cats
Since some of these symptoms (vomiting, weight loss, weakness) are also signs of hyperthyroidism, you may not notice them right away. The most common signs you should watch for include:
- Vomiting or regurgitating undigested food
- No appetite (refusing to eat)
- Rash
- Swelling of the face
- Excessive scratching (especially head, neck, and face)
- Bleeding disorders
- Cold limbs
- Shock
- Seizures
- Liver failure (yellowing of the skin, eyes, and gums, vomiting, lesions anywhere on the body)
- Coma
- Death
Types
Methimazole is a prescription drug made for humans that reduces the amount of thyroid hormones (T3 and T4) your cat’s body produces. It has been accepted for use in cats with hyperthyroidism. This drug also goes by other names such as:
- Felimazole
- Tapazole
Causes of Methimazole Allergy in Cats
The cause of methimazole allergy is the consumption of methimazole. In some cases, the body attacks the drug and this causes histamines to be released, which creates the symptoms such as vomiting, diarrhea, swelling of the face, scratching, hives, shock, and even coma.
Diagnosis of Methimazole Allergy in Cats
The allergy symptoms of methimazole are usually pretty straightforward, but the veterinarian will probably need to rule out other issues before making a diagnosis. Because the drug has many side effects besides the allergy symptoms, the veterinarian may decide to stop the drug immediately anyway. However, a comprehensive physical examination, blood tests, urinalysis, and radiographs will all be needed to ensure there are no underlying conditions besides the hyperthyroidism.
Treatment of Methimazole Allergy in Cats
The treatment for methimazole allergy is the immediate stoppage of the drug. Because hyperthyroidism is a life-threatening condition, other treatment will need to be decided on right away. There are two other choices that veterinarians use for hyperthyroidism, which are radioiodine or surgery.
Radioiodine (I-131)
Radioiodine is a one-time injection that is effective and safe. Because it is radiation, your cat will have to stay in the hospital for several days (by law), but there are no other medications or injections required. It does not damage any other organs or tissues, will not damage the healthy parts of the thyroid glands, and has no serious side effects like the other drugs. The only drawback is the cost, which averages about $1,000, depending on where it is done. Unfortunately, some cats are unable to get the medication because they are not healthy enough. Radioiodine treatment is only able to be done at certain hospitals that have permits for radioisotope use.
Surgery (Thyroidectomy)
Removal of the thyroid glands is a procedure that is usually only done on cats that are relatively healthy (besides the hyperthyroidism) and under 15 years old. Most often, both thyroid glands are removed, but if the veterinarian believes that one is healthy, it will be left to do its job. It is an effective surgery that is done often, but the parathyroid glands are sometimes wrapped around the thyroid glands, making it a difficult process.
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Recovery of Methimazole Allergy in Cats
Hyperthyroidism is a fatal condition that can cause organ failure and death quickly without treatment. If your cat cannot be treated with methimazole, radioiodine will be used, if possible. However, surgery may be the best choice if your cat has allergies.
Methimazole Allergy Questions and Advice from Veterinary Professionals
Bombay
Pawtapper
3 Years
0 found this helpful
0 found this helpful
My pet has the following symptoms:
Licking At Genitals
Excessive Licking
My black Bombay cat who I rescued from outside is about 3 years or so has been excessive licking the vet did bloodwork and found out he has over active thyroid and food allergies also to corn,peas, flaxseed ,soybean, kelp, alfalfa and barley. He has been on methimazole 2.5mg daily for 2 months and he is still excessive licking I am feeding him beyond grain free but it has peas in it. I am going crazy with my cats licking
Tuxedo
Gracie
14 Years
0 found this helpful
0 found this helpful
My pet has the following symptoms:
Puking, Not Eating, Not Drinking
My 14 yr old cat was put on methimazole 5mg 2x a day every 12 hrs for hyperthyroid and after about 2 weeks she is now puking constantly and hasn’t been able to eat or drink at all. I’m very scared this is going to kill her; she’s worse now than before!
Cat
Tiger
15 Years
0 found this helpful
0 found this helpful
My pet has the following symptoms:
Severe Loss Of Appe
Severe Loss Of Appetite
You sound like a great veterinarian. I had to do my own hours of research and found the Y/D Thyroid food for cats with hyperthyroidism. My vet didn't even suggest the Y/D knowing my cat could not tolerate what is IMO, the poison he gave her both in tablet and transdermal gel form, knowing it caused bad side effects of loss of appetite in my already old, underweight cat!! The next visit, I asked him from my own research if I could have a prescription for the Y/D thyroid food for my cat, and he said he doesn't recommend it!!
Cat
Tiger
15 Years
1 found this helpful
1 found this helpful
My pet has the following symptoms:
Loss Of Appetite
My cat was put on tapazole 1/4 tablet for hyperthyroidism and quickly lost her appetite!!! I took her off it, and the vet got a transdermal gel to apply to her ear of the same medication, which caused the same symptoms!!! She's a senior and has always been very small and only weighs 6 lbs., so she can't afford to lose any more weight, but thanks to this poison drug....she did!!!! I gave her the transdermal version of this drug for 2 days, on the 2nd day she completely lost her appetite! Of course I completely took her off the poison drug! Today, it's the 3rd day of her being sick and having no appetite from this poison drug!! My vet put her on the transdermal gel version due to loss of appetite from the pill version! WARNING: Both versions of this POISON drug have the same side effects!! If any one is interested in suing the manufacturer's of this drug, please contact me!!! My baby is fading away due to this drug!!!
domestic short hair
Ivan the Terrible
17 Years
1 found this helpful
1 found this helpful
My pet has the following symptoms:
Lethargy, Itching, Vomiting
Ivan the Terrible was diagnosed with hyperthyroidism three weeks ago. Initially, he seemed to tolerate the Tapazole, but at around the 2 1/2 week mark he began vomiting several times per day and having itchy fits, scratching above his eyes and under his chin. He was also extremely lethargic. The vet has taken him off of the meds and we will try him on the prescription food. As with most cats, he is picky and may not eat it. I doubt that radioiodine therapy will be an option for him given his age, and that I live nowhere near a facility that does the treatment. It may be "don't buy any green bananas" time for old Ivan, but hopefully he'll do the food.
