Methimazole For Cats: Overview, Dosage & Side Effects – The Dog Lovers

Methimazole, for which frequent manufacturers embrace Felimazole and Tapazole, is an oral medicine generally utilized in veterinary drugs to deal with cats with hyperthyroidism. On this article, you’ll study what methimazole is, the way it works, unintended effects to observe for, and a few ceaselessly requested questions.

Medicine Sort:

Antithyroid medicine

Prescription Required?:


Model Names:

Felimazole, Tapazole

Widespread Names:


Obtainable Dosages:

Felimazole tablets: 2.5 and 5mg; generic: 5mg and 10mg

Expiration Vary:

Merchandise must be used earlier than the expiration on the package deal. Tablets must be saved at room temperature and protected against moisture.

About Methimazole For Cats

Hyperthyroidism in Cats

Methimazole is classed as an antithyroid medicine. Primarily, it inhibits the synthesis or manufacturing of thyroid hormone secreted by the thyroid glands. 

Methimazole is a quite common and useful medicine to be used in treating cats with hyperthyroidism the place the thyroid glands produce an excessive amount of thyroid hormone (T4), resulting in chronically debilitating results on the body toàn thân. 

One model of methimazole, known as Felimazole and manufactured by Dechra Prescribed drugs, is FDA accepted to be used in cats. Tapazole, a human model, is often used off-label in cats. There are additionally many generic types of methimazole. 

Though a few therapy strategies for hyperthyroidism can be found, together with methimazole, iodine 131 therapy, surgical elimination of the overactive thyroid gland, and a prescription weight-reduction plan, methimazole’s biggest profit is that it’s a very cheap strategy to get pretty fast management over the illness. 

What Does Methimazole Do For Cats?

Feline hyperthyroidism is a quite common illness in older cats. It’s thought of the commonest endocrine illness that afflicts older cats. 

Additionally Learn: Greatest Mèo Meals For Hyperthyroidism

An endocrine illness is one which considerations glands inside the body toàn thân that produce hormones. Within the case of hyperthyroidism in cats, the glands are producing an excessive amount of T4 and T3 thyroid hormones. 

The impact that an excessive amount of thyroid hormone locations on the body toàn thân can fluctuate from mèo to mèo, however is usually widespread all through the body toàn thân. Excessive thyroid ranges enhance metabolism, basically placing a kitty’s body toàn thân on overdrive.

Classically hyperthyroid cats are often not less than 10 years of age or older, and develop a ravenous urge for food coupled with weight reduction.

Hyperthyroidism in cats is most frequently brought on by a benign tumor of the thyroid glands known as an adenoma. Actually cancerous malignant tumors of the thyroid gland are luckily thought of very uncommon in cats, making medical administration very possible. 

Methimazole blocks the synthesis and launch of thyroid hormone from the thyroid gland, thereby controlling overproduction and the results of the illness. The quantity of hormone manufacturing that’s blocked is determined by the dosage used and every particular person mèo. On this approach nevertheless, methimazole is a drugs that may solely handle, however not remedy, hyperthyroidism.

Aspect Results Of Methimazole For Cats

If cats expertise unintended effects from methimazole they often seem inside the first three months of use.

Many cats tolerate methimazole properly, however there are some extra frequent and unusual opposed results to pay attention to, which most frequently happen inside the first three months of methimazole use. The commonest unintended effects embrace vomiting, lack of urge for food/anorexia, and extreme tiredness/lethargy. 

Gastrointestinal upset results happen in about 10% of cats. In some cats, this can be associated to the bitter style of the pill khung, and hiding it in meals or a deal with might assist. 

Different, extra critical aspect impact abnormalities luckily happen much less generally. Blood problems, lượt thích clotting/platelet points, bleeding, and low cell counts happen in about 4% of cats

Intense facial itching, termed pruritis, might happen in 2% to three% of kitties, and is commonly seen extra rapidly, inside the first three weeks of therapy.

Different uncommon however critical results can embrace liver illness and an immune-mediated dysfunction, each of which happen in lower than 2% of instances. 

Much more not often, a neuromuscular dysfunction known as myasthenia gravis has been seen.

As a result of older cats are extra usually affected by hyperthyroidism, different illnesses might typically already be current that may complicate therapy. The commonest is kidney illness. When hyperthyroidism is current, it drastically will increase the filtration charge within the kidneys, which may masks underlying kidney dysfunction.

This dysfunction might solely be famous after beginning the medicine, because the filtration charge within the kidneys slows down with the normalizing metabolic charge. That is one major motive that lab work rechecks are generally wanted to observe organ operate. 

In cats with reasonable or extreme kidney illness already current, any therapy for hyperthyroidism must be fastidiously mentioned, as remedy is prone to make kidney illness worse. Within the creator’s expertise, therapy even in cats with delicate kidney illness who’re newly identified as hyperthyroid, must be approached cautiously. 

Methimazole might trigger problems in kitties with different problems that could be current, together with diabetes mellitus, liver illness, or any pre-existing blood-related problems or problems of the immune system. 

A number of sorts of drugs might work together with methimazole. It’s essential to make your veterinarian conscious of another drugs or dietary supplements your kitty is at the moment taking when discussing use of methimazole.

Overdoses of methimazole are most definitely to briefly induce the commonest opposed results, lượt thích GI upset and lethargy. Results on the liver might also happen, in addition to blood problems lượt thích anemia and low platelet depend. Results might largely rely on the dose of methimazole and another illnesses a kitty might also have.

If you’re ever involved that your kitty might have developed unintended effects whereas utilizing methimazole, or acquired an overdose of the medicine, make sure that to liên hệ your veterinarian, the ASPCA Animal Poison Control Center (1-888-426-4435), or Pet Poison Helpline (1-855-764-7661) for additional recommendation. 

In people, methimazole is taken into account a teratogen, that means that it may well trigger beginning defects in a growing fetus. Pregnant girls or girls who might turn out to be pregnant, ought to put on gloves when dealing with methimazole, in addition to the litter or any bodily fluids (i.e., urine or vomit) from handled cats.

In cats that do develop digestive upset unintended effects from methimazole, altering to the topical transdermal khung could also be an choice, as abdomen irritation by the pill is bypassed. In cats that develop any of the extra critical unintended effects the place methimazole must be discontinued, different therapy modalities for hyperthyroidism, lượt thích iodine-131, surgical procedure, or a prescription weight-reduction plan can be wanted to handle the illness. 

Methimazole For Cats Dosage

The FDA-approved tên thương hiệu product Felimazole (methimazole) is a pill given by mouth.

Per the label for the FDA-approved product Felimazole for cats, the dose for methimazole begins at 2.5 milligrams per mèo each 12 hours. The dose is then titrated/adjusted relying on recheck lab work after three weeks. The dose ought to solely be adjusted in 2.5-milligram increments.

The utmost complete dose for Felimazole is 20 milligrams per day divided in two 12-hours doses of no more than 10 milligrams every. 

Many cats with hyperthyroidism could also be regulated properly at 2.5 milligrams twice a day, although changes could also be wanted, which is why recheck lab work is so necessary, particularly when beginning out.

In cats that don’t tolerate the pill khung of methimazole, both due to digestive upset results, or a kitty mother or father having issue at trang chủ giving a pill to their mèo, oral liquid and topical transdermal preparations will be formulated by means of compounding pharmacies. 

Whereas simpler to manage, you will need to word that the transdermal preparation usually doesn’t work as effectively or in addition to the oral khung, usually taking longer to succeed in ranges of management, and requiring greater doses. 

The transdermal khung must also at all times be utilized by a human with gloves in order to stop absorption of the medicine by means of their very own pores and skin accidentally. 

For pet mother and father contemplating one of many extra healing therapy choices for hyperthyroidism, lượt thích surgical elimination of the overactive gland or iodine-131 therapy, a short-course of methimazole remains to be usually prescribed to each get signs below management till the process, in addition to to make sure management is feasible and that secondary kidney illness doesn’t develop after thyroid operate returns extra to regular. 


Methimazole is a really generally prescribed medicine for cats with hyperthyroidism. Its advantages are that it really works inside solely a few weeks to manage indicators of the dysfunction, and it is rather cheap. 

Unwanted side effects are typically much less frequent, however are well-documented and potential. Nevertheless, since different therapy strategies could also be much less dependable (prescription weight-reduction plan) or prohibitively costly (surgical procedure and iodine-131 therapy), methimazole nonetheless stays the go-to medicine for administration of this frequent situation. 

Often Requested Questions

What are the unintended effects of methimazole for cats?

There are a number of potential unintended effects that may be seen with methimazole in cats. The commonest embrace digestive upset lượt thích vomiting and poor urge for food, in addition to lethargy. 

Typically GI upset is because of the bitter style of the oral pill, and could also be remedied by discovering a strategy to conceal the style or getting the medicine compounded right into a flavored khung. 

Extra critical unintended effects which can be much less generally seen with methimazole embrace blood problems lượt thích low platelets counts and anemia, liver illness, extreme facial itching, and autoimmune illness. 

Thankfully, in lots of instances, these results will reverse when the medicine is discontinued. However sadly in these instances, use of methimazole in any khung should usually be totally discontinued, and different therapy strategies for hyperthyroidism, lượt thích a prescription weight-reduction plan, surgical procedure, or iodine-131 therapy, have to be pursued as an alternative. 

How lengthy can a mèo reside on methimazole?

This varies, however on common a mèo could also be anticipated to reside wherever from two to 5 years with hyperthyroidism being managed with methimazole. 

Variability on this estimate will be attributable to a number of elements. Youthful cats identified earlier with the illness might have an extended life expectancy than a a lot older mèo who’s identified after results of the illness (similar to weight reduction, blood stress, coronary heart dysfunction, kidney illness) have already taken their toll on the body toàn thân.

Cats with pre-existing illnesses, lượt thích kidney illness, diabetes, or major coronary heart illness might also fare much less properly with therapy of hyperthyroidism typically. 

In line with a examine revealed in 2006 within the Journal of the American Veterinary Medical Affiliation that adopted about 170 cats, about one-third handled with methimazole alone lived for 2 years on common. One other one-third handled with iodine-131 lived for 4 years on common, whereas the remaining one-third who have been handled first with methimazole after which with iodine-131 lived the longest, at about 5 years. 

Understand that with most cats being identified someplace between 10 and 15 years of age (12 years on common), these life expectancy estimates are nonetheless a mèo making it additional into later years with a good high quality of life. 

How lengthy does methimazole take to work in cats?

Oral methimazole has been discovered to succeed in a peak focus within the body toàn thân in solely 30 to 60 minutes. Nevertheless, its impact on indicators and signs of hyperthyroidism do take longer to understand. 

The expectation is that three to 4 weeks after first beginning remedy, the impact the beginning dose has on thyroid operate might be well-represented on bloodwork. If thyroid ranges are nonetheless excessive, it’s then acceptable to extend the dosage. The dosage ought to by no means be elevated or decreased based mostly solely on the looks or indicators a mèo is exhibiting (except we’re seeing an opposed impact or toxicity concern).

The results of hyperthyroidism on the body toàn thân of a kitty, lượt thích weight reduction, muscle loss, secondary coronary heart illness, hypertension, and many others., whereas usually reversible, will often take a number of weeks to vary noticeably. 

What’s the life expectancy of a mèo with hyperthyroidism?

Once more, as equally answered above, the result will be variable, however is commonly not less than two years in cats with no different illnesses complicating issues, lượt thích kidney illness.

General, based mostly on the 2006 examine referred to above, the very best consequence got here from cats first regulated with methimazole who have been then handled with iodine-131, who on common lived for 5 years. 

Iodine-131 is taken into account the last word therapy of selection for cats with hyperthyroidism because the therapy solely targets the overactive thyroid tissue whereas preserving regular tissue. Whereas surgical procedure will also be efficient, your entire gland is eliminated, and if any stray overactive thyroid tissue is current (which known as ectopic thyroid tissue), continued indicators of hyperthyroidism might proceed.

Whereas I-131 and surgical procedure are each thought of cures for hyperthyroidism and recurrence of the illness could be very uncommon, they’re each costlier choices, leaving long-term administration of the illness with methimazole essentially the most viable choice for a lot of of us. 

It’s suspected that administration of hyperthyroidism with methimazole over the long run nonetheless signifies that the illness progresses, simply at a considerably slower charge, doubtless owing to the distinction in consequence utilizing medical administration alone versus pursuing a remedy with I-131.

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