My cat has hyperthyroid, what is safe/best starting dose of Methimazole?

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PH&MonkeyPenPenFaFaTiger

PH&MonkeyPenPenFaFaTiger

Member Since 2020
Hi all,

My cat 15 years old Fafa has mild CKD and confirmed hyperthyroidism. I only have the option to give her meds because they are not i-131 in my area.

It is known that Methimazole has side effects, I worry about it, in particular, it may affect the appetite of Fafa.

Brief research shows me that starting dose of 2.5mg of Methimazole is common, but I don't know if it is the best in my case. I don't fully trust that the vet may give Fafa the best dose. (not that he is incompetent, but for example, he gave Monkey 3.0 U of insulin as starting dose).

I want to seek advice on the best dose. I come here to ask because I feel my brain is struck. I also ask a similar question in the Hyperthyroid cat's facebook group. (https://www.facebook.com/groups/42301610484)
 
One of my vets started Boots at 2.5mg/day. He did not tolerate the pills (stopped eating) and I went to the transdermal@2.5mg once daily. That was increased to 3.75mg once daily which resulted in acceptable T4 value.
Another vet started my Nala (diabetic in remission)@ 2.5ng twice daily. She did not tolerate the pills (hid right after pilling, really hid). I used the 3.75mg transdermal I had for Boots. I then scheduled RadioCat which both of them received last week.
 
The facebook group is an excellent source of information, there is more experience and research there than anywhere else I've found. Well worth waiting for an answer.
The starting dose really depends on what your cat's thyroid numbers are. If he is at the low end of hyperthyroid, starting at half that dose is more reasonable. If it turns out he's at a higher level of hyperthyroid, then the 2.5mg dose may be appropriate. Really depends on his blood test values.

However, it is often recommended to start at the lower, 1.25mg dose for several reasons. First, it is better to under-medicate, retest bloodwork, then increase dosage if necessary, than to over-medicate and throw the cat into a HYPOthyroid condition, which can also be very hard on their bodies, and then necessitates even more medication adjustments and blood tests. Second, there can be side effects from the medicine, especially gastrointestinal problems, so starting at the lower dosage level allows for the cat's guts to get used to the medicine at an easier level, rather than hitting it hard with the full dosage right off. These are the two main reasons for starting at a lower dose and then moving up if bloodwork indicates it is needed.

Other information shows that it is better for the cat to get whatever dosage it needs split into two doses, 12 hours apart (so, half at breakfast, half at dinner, for example). Keeps their thyroid levels at a more constant rate, which is what a normal thyroid would do. All this info can be found on the Facebook page, and people will gladly explain further to you.

The transdermal methimazole is a way to avoid the gastrointestinal distress that some cats get from the pills. Very easy to do, we did it for several years before finally getting our cat to an I-131 place. We'd rub the dose of the creme in one ear in the morning, while wiping out the other ear with just a damp paper towel, then put the evening dose in the second ear at dinner time, while wiping out the first ear that time. This way, you alternate which ear gets the dose, and keep the other ear clear of build-up from the cream applications (residual can build up and therefore kind of block the new doses from being absorbed, due to the pile up of the gunk layer.) Cat quickly learned to tolerate getting his ears smeared, no stomach distress, worked well until his HT disease progressed to too high a level and we really had to get the I-131 done (eventually the benign thyroid tumor grows too large and turns cancerous, at that point you either do something drastic like surgery or I-131, or you just make the cat as comfortable as possible until the now-soon end.)

Many cats go many years on HT medicine and do quite well, the speed at which the disease progresses can vary greatly, in some it's very very slow, in others not so slow, but it is definitely treatable and even curable with the 1-131.
 
Sharing this if you should decide to treat using the pills. I treated one of my cats with methimazole over 20 years ago so I can't remember the dosage amount. She was nearly impossible to pill and I did not want that struggle every day, so instead of pilling her, I crushed the tablet and gave it in her food. Using Fancy Feast Classic Beef Feast, I poured the juice from the can into her bowl and added the crushed pill. She would lick it up entirely, so I believe it was tasteless. As soon as the juice was consumed, I gave her the beef pate. Her appetite was not effected. Over time I she developed dental issues and I treated her for glaucoma, but she lived to just short of 20 years old.
 
Gracie85 said:
The facebook group is an excellent source of information, there is more experience and research there than anywhere else I've found. Well worth waiting for an answer.
The starting dose really depends on what your cat's thyroid numbers are. If he is at the low end of hyperthyroid, starting at half that dose is more reasonable. If it turns out he's at a higher level of hyperthyroid, then the 2.5mg dose may be appropriate. Really depends on his blood test values.

However, it is often recommended to start at the lower, 1.25mg dose for several reasons. First, it is better to under-medicate, retest bloodwork, then increase dosage if necessary, than to over-medicate and throw the cat into a HYPOthyroid condition, which can also be very hard on their bodies, and then necessitates even more medication adjustments and blood tests. Second, there can be side effects from the medicine, especially gastrointestinal problems, so starting at the lower dosage level allows for the cat's guts to get used to the medicine at an easier level, rather than hitting it hard with the full dosage right off. These are the two main reasons for starting at a lower dose and then moving up if bloodwork indicates it is needed.

Other information shows that it is better for the cat to get whatever dosage it needs split into two doses, 12 hours apart (so, half at breakfast, half at dinner, for example). Keeps their thyroid levels at a more constant rate, which is what a normal thyroid would do. All this info can be found on the Facebook page, and people will gladly explain further to you.

The transdermal methimazole is a way to avoid the gastrointestinal distress that some cats get from the pills. Very easy to do, we did it for several years before finally getting our cat to an I-131 place. We'd rub the dose of the creme in one ear in the morning, while wiping out the other ear with just a damp paper towel, then put the evening dose in the second ear at dinner time, while wiping out the first ear that time. This way, you alternate which ear gets the dose, and keep the other ear clear of build-up from the cream applications (residual can build up and therefore kind of block the new doses from being absorbed, due to the pile up of the gunk layer.) Cat quickly learned to tolerate getting his ears smeared, no stomach distress, worked well until his HT disease progressed to too high a level and we really had to get the I-131 done (eventually the benign thyroid tumor grows too large and turns cancerous, at that point you either do something drastic like surgery or I-131, or you just make the cat as comfortable as possible until the now-soon end.)

Many cats go many years on HT medicine and do quite well, the speed at which the disease progresses can vary greatly, in some it's very very slow, in others not so slow, but it is definitely treatable and even curable with the 1-131.
Click to expand...
I think this just about covers it all ^

We dose twice a day. His numbers were quite high (9.2ug/dL) so we started at 2.5mg split into two doses. We get it compounded, he definitely doesn't like it but it's better than pilling. Retested after a month, just barely over normal range so now we're at 5mg split into two doses.

We chose not to do the transdermal for two reasons:
  1. Studies have shown it's not always as consistent/efficient as the pill
  2. I am pregnant, and we also have two little kids in the house so we did not want to risk any skin contact at all. There are several major warnings on the methimazole data sheet about pregnant/lactating women as well as children.
Same warnings apply when handling bodily fluids (vomit, feces, urine).

We have not noticed any of the usual side effects, but his WBC, neutrophils and lymphocytes have dropped (this is one of the more rare side effects).

We are also fortunate that his kidneys held up, as treating the thyroid can unmask kidney problems.
 
Update: The vet gave me 5mg carbimazole per day dosage, and I think 2.5mg per day is better. Plus the waiting line is too long for Fafa (3 hours), and I worried that the stress would trigger some disease such as CKD and hyperthyroid, so I will just switch to another vet and request 2.5mg per day, in pill form, because Fafa does not have problem with eating a pill.

If the pill causes side-effects, I would switch to gel
 
Larry and Kitties said:
One of my vets started Boots at 2.5mg/day. He did not tolerate the pills (stopped eating) and I went to the transdermal@2.5mg once daily. That was increased to 3.75mg once daily which resulted in acceptable T4 value.
Another vet started my Nala (diabetic in remission)@ 2.5ng twice daily. She did not tolerate the pills (hid right after pilling, really hid). I used the 3.75mg transdermal I had for Boots. I then scheduled RadioCat which both of them received last week.
Click to expand...

Thanks for your input. So 2.5mg/day can already cause problem, my vet just gave me 5mg per day which I don't agree, so I am going switch to another vet.
 
Gracie85 said:
The facebook group is an excellent source of information, there is more experience and research there than anywhere else I've found. Well worth waiting for an answer.
The starting dose really depends on what your cat's thyroid numbers are. If he is at the low end of hyperthyroid, starting at half that dose is more reasonable. If it turns out he's at a higher level of hyperthyroid, then the 2.5mg dose may be appropriate. Really depends on his blood test values.

However, it is often recommended to start at the lower, 1.25mg dose for several reasons. First, it is better to under-medicate, retest bloodwork, then increase dosage if necessary, than to over-medicate and throw the cat into a HYPOthyroid condition, which can also be very hard on their bodies, and then necessitates even more medication adjustments and blood tests. Second, there can be side effects from the medicine, especially gastrointestinal problems, so starting at the lower dosage level allows for the cat's guts to get used to the medicine at an easier level, rather than hitting it hard with the full dosage right off. These are the two main reasons for starting at a lower dose and then moving up if bloodwork indicates it is needed.

Other information shows that it is better for the cat to get whatever dosage it needs split into two doses, 12 hours apart (so, half at breakfast, half at dinner, for example). Keeps their thyroid levels at a more constant rate, which is what a normal thyroid would do. All this info can be found on the Facebook page, and people will gladly explain further to you.

The transdermal methimazole is a way to avoid the gastrointestinal distress that some cats get from the pills. Very easy to do, we did it for several years before finally getting our cat to an I-131 place. We'd rub the dose of the creme in one ear in the morning, while wiping out the other ear with just a damp paper towel, then put the evening dose in the second ear at dinner time, while wiping out the first ear that time. This way, you alternate which ear gets the dose, and keep the other ear clear of build-up from the cream applications (residual can build up and therefore kind of block the new doses from being absorbed, due to the pile up of the gunk layer.) Cat quickly learned to tolerate getting his ears smeared, no stomach distress, worked well until his HT disease progressed to too high a level and we really had to get the I-131 done (eventually the benign thyroid tumor grows too large and turns cancerous, at that point you either do something drastic like surgery or I-131, or you just make the cat as comfortable as possible until the now-soon end.)

Many cats go many years on HT medicine and do quite well, the speed at which the disease progresses can vary greatly, in some it's very very slow, in others not so slow, but it is definitely treatable and even curable with the 1-131.
Click to expand...

Thanks for your input, you make my head clear.

The vet I just saw, tell me to give 5mg /day pill, and feed only once per day. He made me doubt and your input confirms that he may not be the best person for treating Fafa. Now I am going to switch to another vet.

I will remember your advice for applying the gel when I needed to. Also it is nice to know that it is very treatable. :)
 
Linda and Newman said:
Sharing this if you should decide to treat using the pills. I treated one of my cats with methimazole over 20 years ago so I can't remember the dosage amount. She was nearly impossible to pill and I did not want that struggle every day, so instead of pilling her, I crushed the tablet and gave it in her food. Using Fancy Feast Classic Beef Feast, I poured the juice from the can into her bowl and added the crushed pill. She would lick it up entirely, so I believe it was tasteless. As soon as the juice was consumed, I gave her the beef pate. Her appetite was not effected. Over time I she developed dental issues and I treated her for glaucoma, but she lived to just short of 20 years old.
Click to expand...

Thanks, that is a piece of handy advice. =)
 
FrostD said:
I think this just about covers it all ^

We dose twice a day. His numbers were quite high (9.2ug/dL) so we started at 2.5mg split into two doses. We get it compounded, he definitely doesn't like it but it's better than pilling. Retested after a month, just barely over normal range so now we're at 5mg split into two doses.

We chose not to do the transdermal for two reasons:
  1. Studies have shown it's not always as consistent/efficient as the pill
  2. I am pregnant, and we also have two little kids in the house so we did not want to risk any skin contact at all. There are several major warnings on the methimazole data sheet about pregnant/lactating women as well as children.
Same warnings apply when handling bodily fluids (vomit, feces, urine).

We have not noticed any of the usual side effects, but his WBC, neutrophils and lymphocytes have dropped (this is one of the more rare side effects).

We are also fortunate that his kidneys held up, as treating the thyroid can unmask kidney problems.
Click to expand...

After hearing your advice, plus finding out that Fafa does not seem to have problem eating pills, I will first use pills first (plus it is cheaper)
, if it goes wrong then I would use gel. Also, I will look for the WBC etc you mentioned!
 
I think it's better to start lower at 1.25mg twice a day - but that's harder with the pills you have. You probably just have to do 2.5mg once a day.

You're supposed to recheck labs in a month - but watch for signs of kidney disease in the meantime! Depending on lab results then you'd increase.

My cat was 9.2ug/dL at diagnosis, so we started at a higher dose (2.5mg twice a day). That barely brought him into normal range, so now we're at 5mg twice a day.
 
Personally, I would start at the 1.25mg twice a day. If you can't find a new vet very quickly, perhaps ask your current vet for a lower dose pill? If they won't listen to your reasoning, then make up some excuse like you found your cat barfs up the full 5mg, but didn't when you split the dose in half, or something like that. We also found that thyroid pills are MUCH cheaper through your local pharmacy than through the vet. They can give you a prescription to take there (some won't, then you find another vet. We had a vet charging us $2 per pill for stuff that we could get for 5 CENTS per pill elsewhere!)

It's much easier to go up based on results and then recheck than to go down, wait for things to stabilize, then work on increasing from there.
And a cat that goes HYPOthyroid gets really really sick. I know this because when they did the I-131 on our cat, he got over-treated (which was fine, his thyroid levels had risen to over 22ug/dl, which indicates the tumor is going malignant; so better to over-treat and make sure it's all, completely, gone rather than miss a little bit of it and it aggressively grows back). Two months after treatment he was listless, no appetite, no activity, losing so much fur that he, a tiger cat, lost his stripes, you'd pet him and at the end of the stroke you had a full handful of hair. Cat was barely maintaining living. Blood test showed his thyroid at 0.9. So now he gets his levothyroxin twice a day, and he's his normal cranky old self again, and his stripes are back and his fur is thick. Treating hypothyroid is easy, we check his levels about twice a year but he's stable now. (Just don't want this story to put you off considering I-131 in the future.)
 
As for feeding once a day, Nope! Teaches your cat to gorge itself, more likely to trigger the scarf-n-barf syndrome, and to me, at least, seems a bit cruel.

Our cats get four meals a day, because we developed a scarf-n-barfer, and the borderline diabetic one responded so well to four smaller, high protein very low carb mealsa day that we have managed to keep him off insulin.
 
Oh yeah, the warnings about watching kidney function are because when a cat's body is in a hyped up state from an overactive thyroid, it can mask kidney disease, as the increased blood pressure and metabolic activity overcomes the kidney problems, so as you regulate the thyroid, the true state of kidney function shows up. So blood tests should include kidney testing as well, at least until he's well regulated.
On the other hand, hyperthyroid can make it look like a cat has liver disease, which then resolves when his thyroid is regulated, seen people worried that their cat has too many illnesses to try to treat and continue, but it's really just "side effects" of the hyperthyroid, so you just watch these other things until thyroid is regulated and you can then see what's really going on with the rest of him.
 
Gracie85 said:
As for feeding once a day, Nope! Teaches your cat to gorge itself, more likely to trigger the scarf-n-barf syndrome, and to me, at least, seems a bit cruel.

Our cats get four meals a day, because we developed a scarf-n-barfer, and the borderline diabetic one responded so well to four smaller, high protein very low carb mealsa day that we have managed to keep him off insulin.
Click to expand...

Oh maybe I said it wrongly. I ask about feeding the cat pill once per day. After asking people in hyperthyroid Facebook group, I am aware that pill twice a day is superior to once per day.
Nice to hear that your kitties are doing fine.
 
Gracie85 said:
Personally, I would start at the 1.25mg twice a day. If you can't find a new vet very quickly, perhaps ask your current vet for a lower dose pill? If they won't listen to your reasoning, then make up some excuse like you found your cat barfs up the full 5mg, but didn't when you split the dose in half, or something like that. We also found that thyroid pills are MUCH cheaper through your local pharmacy than through the vet. They can give you a prescription to take there (some won't, then you find another vet. We had a vet charging us $2 per pill for stuff that we could get for 5 CENTS per pill elsewhere!)

It's much easier to go up based on results and then recheck than to go down, wait for things to stabilize, then work on increasing from there.
And a cat that goes HYPOthyroid gets really really sick. I know this because when they did the I-131 on our cat, he got over-treated (which was fine, his thyroid levels had risen to over 22ug/dl, which indicates the tumor is going malignant; so better to over-treat and make sure it's all, completely, gone rather than miss a little bit of it and it aggressively grows back). Two months after treatment he was listless, no appetite, no activity, losing so much fur that he, a tiger cat, lost his stripes, you'd pet him and at the end of the stroke you had a full handful of hair. Cat was barely maintaining living. Blood test showed his thyroid at 0.9. So now he gets his levothyroxin twice a day, and he's his normal cranky old self again, and his stripes are back and his fur is thick. Treating hypothyroid is easy, we check his levels about twice a year but he's stable now. (Just don't want this story to put you off considering I-131 in the future.)
Click to expand...

Hi Gracie, luckily we can find a new vet. So we decide to just ditch that vet. So buying through a local pharmacy is a nice tip too, I can easily get that in Hong Kong without prescription (yes, it is how things work in the pharmacies of Hong Kong)
I will take your advice and be careful of hypo. I would like to have I-131 when it is available in Hong Kong.
 
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