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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
Lynx Point Siamese Mix
Bella
16 Years
3 found this helpful
3 found this helpful
My pet has the following symptoms:
Sneezing
Crying
Excessive Hunger
Excessive Urination
Spinning
Excessive Bad Behavior
Aggressive At Times
Excessive Energy
Refusal To Eat Medicated Food
Hi Dr.'s,
I'm not sure what to do. My cat has hyperthyroid and is extremely allergic to meds (eyes bleeding with yellow pus, severe vomiting all day, scratching to bleeding in ears and eyes, hair falling out in clumps and weird bleeding sores on paws). She also has stage 3 kidney disease (beginning at 2.9), and my Vet says she will not be able to do the iodine treatment. After 5 days of Hills y/d canned food, she refuses to eat at all. Unless it's her usual Nature's Variety Raw canned foods- I only feed her the poultry options (turkey, duck, chicken), and occassionally venison, rabbit or lamb. She is howling often now in the afternoons and evening and wakes me up constantly every evening. She has excessive urine and thirst. I am supplementing Mary Ruth's organic liquid cat probiotics, Pet WellBeing Kidney Support Gold, Aminavast for cats (1x per day, she cannot tolerate the twice per day recommendation), plus one drop of ionic liquid zinc per day in her water. All this seemed to help for about 3 weeks, but now she is exhibiting bad behavior - clawing into leather purses, exercise equipment- all for attention to get her salmon flavor greenies (I stopped feeding her any fish meals) all day long- she could eat them as meals. Is there any help for Bella? She is a just turned 16yr old Lynx Point Siamese Mix. I don't know what to do and I don't want her to suffer. I feel I have no more options if she can't withstand the iodine, surgery and is severely allergic to medicine. She seems to be going a bit crazy spinning around sometimes, she has beginning dementia (dx by vet) as she sometimes stares at a corner for long periods, and running all over and crying. When she is her "old self" she's playful with her toys, naps and purrs- these times seem to be first thing in the morning till about noon. After that starts the onslaught of crying and chaos intermittently throughout the day until evening. I would be heartbroken to put her down, but if she's in pain and suffering, and I can't tell, I would be sad as well. I don't want her to suffer. I just don't know what to do anymore. I read a study where the homeopathic tx Nature muriaticum 200 ck helped the hyperthyroid in some cats, but I've been afraid to give her the one pellet dosage as it did make some cats worse. Thank you so much for any help you can offer.
March 27, 2018
Answered by Dr. Michele K. DVM
3 Recommendations
I'm sorry that Bella is having so many problems - kidney and thyroid disease can be a very tricky combination to manage. I am unable to comment on whether she may be suffering, but if she won't cooperate with the Y/D food, she needs to eat. There are different formulations of methimazole that she may tolerate better, such as the topical formulation. It may be worth having a consultation with an internal medicine specialist to get their opinion on her situation. I hope that you are able to find a solution to keep her comfortable.
March 28, 2018
Also, sorry, I forgot to add.. she weighs 5lbs now, down from 5lbs 4 oz. Thank you.
March 27, 2018
Bella's Owner
She also gets a 1/2 the dosage of liquid CoQ10 for cats.
March 27, 2018
Bella's Owner
Thank you Dr. Michelle... I appreciate your time! Unfortunately, my veterinarian said Bella would not tolerate the topical either. I'll check on a consultation with an internal medicine specialist for a second opinion. Thank you so much again!
March 28, 2018
Bella's Owner
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Russian Blue
Miss t
12 Years
2 found this helpful
2 found this helpful
My pet has the following symptoms:
Losing Weight,
My 12 yr. old cat was diagnosed a month ago with thyroid disease. After being on Methimazole for that time, her levels were retested. Her Alt and Alt which had been normal were thru the roof so we stopped the meds
Vet said she looked like a good candidate for iodine therapy. Other than the cost, would her reaction to the Methimazole be a contraindication to the procedure. Oh yes, her thyroid levels had come down while on the gel
March 21, 2018
2 Recommendations
Radioiodine is a treatment option for hyperthyroidism in cats and is generally considered to be safer than other options, if you are considering using radioiodine you should withdraw Miss T from methimazole therapy for around five days before switching to radioiodine; you should discuss this with your Veterinarian. Regards Dr Callum Turner DVM
http://veterinarynews.dvm360.com/hyperthyroidism-cats-can-live-normal-life
March 21, 2018
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American Shorthair
Amy
13 Years
1 found this helpful
1 found this helpful
My pet has the following symptoms:
Twtiching, Itchin
Twtiching, Itching
My 13 year old cat for the past three plus months seems to get these “fits” where she “hits and wacks” her ears and then sometimes her body completely twitches. She could be sleeping and then all of a sudden start hitting her ear and squirm and shake about. This can last from a few minutes to an entire evening. I brought this up to our vet to see if it is something neurological or an allergy.
Now for the past year my Little Amy takes daily Methimazole in Lipoderm 5 mg./0.05ml T-A-D Trnsdrm gel 1.5ml for her thyroid. It is applied to her inner ear flap, alternating ears each day and she has been on this medication now for one year. She also gets her ears cleaned 2X a week to prevent buildup. Could it be the meds causing the twitching? I don’t want this to escalate into something I can’t reverse or control. First, I don’t even know what this is and what is causing it. So should I see a specialist or return to my regular vet and ask her to check further into it based on what you might think this is.
email: muchobasura2@gmail.com
March 17, 2018
1 Recommendations
Facial excoriation is a noted side effect of methimazole therapy, facial excoriation is the repeated hitting of the face to the point of self trauma; the twitching of the muscles may be related to low blood calcium, this is something you should discuss with your Veterinarian after blood tests and an examination. Regards Dr Callum Turner DVM
March 17, 2018
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Domestic short haired tabby
Tabi
14 Years
3 found this helpful
3 found this helpful
My pet has the following symptoms:
Vomiting And Diarehha
My cat started Methimazole early December, her thyroid went too low and they decreased the dose. Still showing even lower at her next blood test the vet took her off for a month, now thyroid is high again. Now trying the food but my cat is refusing to eat it, and when she does its very small amounts. The vet said if she wont eat the food (shes really fussy) they'd try an even lower amount of the methimazole. My concern is the fact she was scratching her head above her eyes and there was bleeding and scabbing, is this something that will likely return with any dose as its an allergy? Or it may not happen due to the lower dose and it was just a matter of too much methimazole?
Feb. 28, 2018
3 Recommendations
Treating hormonal conditions like this are difficult as the problem is never the same in each animal and you need to balance the medication to hit within the reference range (or as near as you can to it); it is possible that there was some scratching as a side effect of the treatment but I cannot say if it will return with a lower dose or not, it may not be related to treatment. Regards Dr Callum Turner DVM
Feb. 28, 2018
Thank you for the reply. The scratching was from the medication for sure as it has been the only time she has ever done this. Within one week of taking her off she stopped and it healed up. My concern was that it may be an allergic reaction in which case I'd be worried if she had to go back on, even at the much lower dose.
Feb. 28, 2018
Tabi's Owner
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dsh
Apollo
11 Years
1 found this helpful
1 found this helpful
My pet has the following symptoms:
Vomiting
My 11yo DSH neutered male cat was diagnosed with hyperthyroidism. We began a Methimazole pill regimen (2.5 mg twice a day). After four days, he began vomiting regularly. The vomiting was not concurrent with the pilling or with feedings. Generally, the vomiting occurred between 4-6 hours after his pill.
He also became jaundiced, then stopped eating completely. The Methimazole pills were discontinued immediately. An exam revealed probable pancreatitis (not fatty liver).
After he recovered, we began transdermal Methimazole, in roughly the same 2.5mg concentration, applied twice a day (alternating ears with each application). After 9 doses, his vomiting resumed. As before, it occurred 4-6 hours after the Methimazole application.
He is now on Hills y/d food, but has shown a lack of interest in the food (dry kibble) at times. He has not stopped eating, but it's clear he does not like the y/d food.
I am looking for other treatment options.
Feb. 17, 2018
Answered by Dr. Michele K. DVM
1 Recommendations
Thank you for your email. Apollo may benefit from radioactive iodine treatment - that is one option for treating hyperthyroidism in cats, but it is only beneficial if he has adequate kidney function. Your veterinarian can discuss this option with you, whether it is possible, and where it may be performed, as only specialty hospitals tend to administer the treatment.
Feb. 17, 2018
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Domesticated
Sweety
12 Years
0 found this helpful
0 found this helpful
My pet has the following symptoms:
Wobbly Rear Gait, Cock-Eyed
My 12 year old feral cat, about a year old (prob younger) when we moved here, was always a nimble, sleek and healthy cat. Like a gray panther, sometimes we'd call her Fangs, but her name is Sweety. It's what I called her to lure her to us. Suddenly her tail coat 'went flat'. Thought it was age. Later she began to eat veraciously. Then her whole coat went scrappy. As I was waiting to take her to the vet, she got a neuro problem where her head was cocked to the side. She was Dx'd positive w/Hyperthyroidism and started on .5ml Methimazole twice a day. Really was hard to do so vet said 1ml once a day. Her first blood test 3 weeks later showed an improvement in T4, but was still slightly above range, 1 bar, the vet liked it there for force of blood to kidneys. No symptoms improved. Just took her in a couple days ago for next set of labs, and today, I couldn't get her out of her cat house. We pulled her out and she could hardly walk. Stupid me gave her medication and she drunkily walked away. Thought she had to pee/poop but she hasn't returned. All I can say is this medication (Wedgewood liquid) made her worse, has not once benefited her. If she comes back, I'll keep her inside (she has a heated cat house on the porch that is nice and warm) but will not administer this crap to her anymore. Figure out what to do from here. Perhaps RadioCat is the solution, but she is in really bad shape. In the world of Rx for humans, I know there are complications from one person to the next with all the mfrs, but I believe it is better to control hypo-thyroid vs hyper. Vets may be better off to offer thyroidectomy and administer T4 to raise it, than offer THIS drug to lower it. I feel like this made her worse.
orange short hair
Brooklyn
15 Years
0 found this helpful
0 found this helpful
My pet has the following symptoms:
Hypothyroidism
My cat Brooklyn diagnosed with hypothyroidism at a high level 11.7 he was put on 5mg transdermal methimazole 2x daily, seemed to be o.k. he ate alot as well as slept, lots of itching the face area. on his thirty day follow up blood test he is in a healthy thyroid range of 1.7 a very significant drop of the very high level he was at. My concern is the vet wants me to keep him on the 5mg. 2x a day for 6 more months till his next blood work follow up. I think it is too much medication and I want to administer the medication only once a day, I am not getting any real feed back from the vet only the front desk just reads the report to me and to continue the same dosage, I really want it lowered, I am not a vet but 2x a day at 5mg. for another 6 months seems high especially when my cats levels drop significantly to normal levels. He is very finicky, but now cooking natural foods for him. What do you suggest I do about the dosage?
Shorthair
Birdie
13 Years
0 found this helpful
0 found this helpful
My pet has the following symptoms:
Jerking
Muscle Spasms
Seizures, Twitching,
Birdie started twitching within week of taking methamzole liquid oral dosing , And full blown seizures, she’s on phenobarbitals and we are waiting, she still twitches . Trying to find out the liquid base ingredient and so far company actually refused
dsh
Emma
15 Years
0 found this helpful
0 found this helpful
First off, thank you all for sharing. Seems to me this drug is not very good for cats. My 15 yr old Emma was recently diagnoised with Hyperthyroid. The vet told me about the drug option or iodine. I picked the drug thinking she won't be the percentage that reacts badly to it, WRONG!
We started on a very, very low dose of 1/2 a 2.5mg 1 x a day for 7 days (then was going to go up to 1/2 chew two x's a day making it the full dose - she is a small 8lb cat) I didn't even make it to the 7th day, stopped medicine on 5th day). She was vomiting and stopped eating, lack of energy. I got the meds compounded from Wedgewood Pharma in New Jersey.
To get her to eat again has been a challenge. I appreciate people mentioning the loss of smell issue and that makes cats not want to eat what they can't smell. I basically forced fresh cooked chicken and canned tuna into her mouth so she would taste it. She finally starting eating some. I'm pretty sure (hoping) her appetite will come back in full.
Now I'm debating about the iodine treatment. I did talk to friends that had it done to two of their cats with success in Santa Cruz, CA. I would be going to Radiocat in Redwood City, CA. She hates bloodwork (takes 4 of us to hold her - gonna try a kitty straightjacket LOL, catbag next time) and I feel bad leaving her there three days, but may not be alternative. I'm very lucky that financially I can swing it. She is a tough cat and I'm hoping she'll live another 5 years ;-)
I wouldn't recommend this med to anyone. Even my Vet told me that her two cats reacted badly and she did the iodine treatment. HELLO... you could have told me that when I brought my cat in to see you. I know there may be some cats that don't react badly and do well. I'd be curious to hear those stories. Take care everyone.
American Short Hair
Valentine
16 Years
0 found this helpful
0 found this helpful
My pet has the following symptoms:
Lethargy, Rear Leg Weakness
My kitty was diagnosed with borderline hyperthyroidism and given 2.5 methimazole twice a day. She also has kidney disease which was being managed . She was on it for 4 weeks and at that time stopped eating and was very lethargic. Vet said it wasn't the med . I finally cut her dosage at night and she is eating. I think she should have been monitored and not have been medicated till 3 month checkup because now she is having hind leg weakness
