Hyperthyroidism in Cats


Drinking more water - Hyperthyroid cat

Question: Hi Dr. Mike, My cat Sam, a 13-year old Tabby, was drinking more water than normal recently and I became concerned. We took her to the vet and he believes she may have CRF. Here are her readings: Bun 26.0 (Range 16.0 - 36.0) Crea 2.76 (0.80 - 2.40) Glu 152.6 (76.0-145.) Obviously the Creatinine is higher than normal. He has her on Hills K/D, has run a urinanalysis, taken xrays and is sending us to have an ultrasound. He's trying to rule out everything else. While Sam is eating the K/D, and we're waiting for other tests to come through, I've read just about everything you've posted on your site about CRF and you mention Sub-Q fluid quite a bit. I have two questions, first: If in fact she does have CRF, WHEN do we decide to start Sub-Q fluids. It's not that I'm looking forward to doing it, but I want to do as much as I can at the start of this disease as possible and I wanted your opinion. My vet says that may be warranted, but he didn't say when, probalby because he's still waiting for other tests. But if her creatinine is at 2.76 now, should we start it now? Second: Sam is hyperthyroid and on Tapazol. My vet has me cutting it back a bit right now to see if that helps. He feels it's a balancing act with a hyperthyroid cat. How do you feel about decreasing the Tapazol to see if it helps? Thanks Dr. Mike, Jeanne Answer: Jeanne- The labwork probably does indicate that there is some degree of kidney insufficiency but that at the present time Sam's kidneys are able to compensate for it pretty well. The BUN is a better indicator of the immediate state of the kidneys and the creatinine a little better indicator of the long term trend. Cats with hyperthyroidism often have kidney damage but paradoxically, hyperthyroidism often masks kidney damage. For this reason, it is a good idea to carefully monitor the T4 level when evaluating the situation and keeping it in mind when looking at BUN, creatinine, phosphorous and potassium levels. Try to rule out hypertension (high blood pressure) as a contributing cause, consider supplementation of potassium and think about the use of k/d, as the current recommendations in cats are to use low protein diets when the creatinine is above 3.5 or the BUN above 75 (or both) and to use less protein restriction prior to these levels as there is some evidence that starting protein restriction too soon may contribute to the loss of kidney function rather than helping prevent loss. In a hyperthyroid cat it is a little harder to figure out the real degree of kidney function loss and your vet may be thinking that it is worse than it appears. Measuring the T4 level is helpful in determining this. If it is well controlled (upper half of normal but not above) it would be less likely to be hiding kidney function loss but this is still partially dependent of blood pressure. A lot of vets are currently trying to keep the T4 level just slightly above normal in hyperthyroid cats with signs of kidney failure in the hopes of getting some kidney protection effect while still controlling the other effects of hyperthyroidism. We just try to keep the level in the upper half of normal but I don't try to change doses if the T4 is just slightly above normal. Early in kidney failure we usually try to concentrate on controlling blood pressure if it is high, supplementing potassium if it is low (or even low normal), keeping cats hydrated and using either phosphorous binders or calcitriol to try to control secondary hyperparathyroidism, a condition that occurs eventually in almost all kidney failure patients. Calcitriol use is still controversial but it seems to help based on our clinical observations and so we do try to use it when owners are willing and feel that they can administer medication on a daily basis. Hydration is a really critical issue. Cats often drink less than they should. It is possible to encourage cats to drink by doing things like using a "cat fountain" which can be purchased at many pet stores or from pet supply catalogs, putting ice cubes in one water bowl if the cat likes ice, putting water in interesting containers like water glasses and changing from dry food to canned food since canned food is about 80% water. When the BUN rises above 75 or so, then we usually advocate using subcutaneous fluid therapy and keeping it up as long as is necessary to control the rise in BUN. For some cats the use can be very intermittent and in others fluids have to be given daily to help control rises in BUN. To sum this up, this is probably early in the kidney failure process for Sam but it is a little hard to be sure of that due to the hyperthyroidism. Concentrating on controlling high blood pressure, supplementing potassium, keeping hydration as normal as possible and using phosphorous binders or calcitriol is probably a good idea. Restricted protein diets like k/d may be OK but it is probably a little early to use them based on the most current thinking among people who study that issue -- although lots of vets would argue that their clinical experience is that these diets help more often than they hurt. I hope that this is helpful. Mike Richards, DVM 10/7/2003

Methimazole (Tapazole Rx), Hyperthyroid cat vomiting with nausea

Question: Dear Dr. Richards,

I have a hyperthyroid 17 year old male cat. He has been on 3.75 mg of tapazole (1.25 in the am & 2.50 in the pm) a day since the end of July. He has a hard time with nausea and vomiting. What can be done to lessen / eliminate and nausea and vomiting, so we can get him stabilized for surgery or the radioactive iodine treatment?

He was starting to develop fatty liver disease, but I believe that has been arrested. My vet put a feeding tube in him which has been helpful. I have been getting around 100 cc of Hills AD in him everyday. I'm trying to get it up to 140 cc a day, but it is very difficult with the nausea and vomiting. I also give him 2.5 mg of metoclopramide three times a day (around 6 AM, noon & 6 PM) about 15 minutes before I feed him. I also give him 5 mg of Pepcid AC at night. The Pepcid has been very helpful. He used to vomit like clockwork at 4:00 AM every morning. The Pepcid seems to have eliminated that almost entirely. I also give him one gel capsule (amount?) of milk thistle once a day to help with his liver.

He blood has been tested several times. I don't have specific test results, but my vet was very pleased with the results on his kidneys. His BUN and creatin levels are within normal range. His electrolytes are fine. His T4 levels have been between 2 and 4. Everything that was tested was within normal limits, except for his liver enzymes (I don't know which ones - there was only one reading). They were/are very high. We tried taking him off tapazole for a weekend and he got even sicker (more vomiting, lethargy, etc.). My vet thinks his hyperthyroidism, or possibly the tapazole, is elevating the liver enzymes, and that these high liver enzymes may be causing the nausea and vomiting. She mentioned there was a new replacement for tapazole, but that it had not been well tested. She has not recommended that we try this other drug.

He has been Xrayed. We also did an ultrasound last week and everything looked fine - no obstructions. He is urinating fine and still having bowel movements, although I have to give him a couple of CCs of lactalose every once in a while to help with this.

I think his weight has stayed the same or maybe increased a little. He is down to around 6 lbs. Normally, we was between 8 and 9 lbs. He sleeps a lot. He still gets up and goes to the bathroom. He purrs when I feed him (if he is not nauseated). He still seems to have the will to live.

He has had his thyroid surgically removed 3 times within the past 4 years. He has been on tapazole before (prior to each surgery) and seemed to tolerate it alright. We did have some problems with his appetite prior to the last surgery in March of 2000. We had to decrease the tapazole dose and give him appetite enhancers. He did fine after this last surgery. We had him on some thyroxine for a little while after surgery and eventually discontinued it.

He showed few of his normal signs of being hyperthyroid, until about a month ago when he started vomiting and totally lost his appetite. That happened the last time he became hyperthyroid, but he started eating again once we started him on tapazole. I would like to get him built up again and then have the radioactive iodine treatment, since there always seem to be small traces of the thyroid tumor left after surgery.

What can we do to eliminate / reduce the nausea and vomiting so we can get him stabilized for this treatment? I don't want to give up on him at this point, since he seems to be in good shape otherwise. Is there something else besides tapazole that he can take? What do you think is affecting his liver? Are the high liver enzymes causing the nausea?

This has been extremely frustrating. A prompt rely would be VERY MUCH appreciated, as I feel we are running out of time. I believe I have a very competent vet. I'm just at my wit's end.

Thank you,


Answer: Ann-

Methimazole (Tapazole Rx) causes vomiting in about 10% of cats treated with it. In most cats this resolves even if the methimazole administration is continued. However, a few cats have continuous problems with vomiting or diarrhea as long as methimazole is administered. This effect is somewhat dose dependent but it doesn't seem like you are getting really good control at the present dosage, so cutting it wouldn't be a good idea. There is a small chance that increasing the dosage might be helpful, just in case the vomiting is more related to thyroid levels than to the medications. We try to keep the T4 in the lower half of the normal range when using methimazole and I think that the levels in your note would be in the upper half of the range. This is something to consider if you can't go directly to radioactive iodine therapy.

You could try alternative oral medications. There are several that will work, including propylthiouracil, carbamizole and ipodate and iopanoic acid. Of these, the ipodate is the most readily available. It works for about 80% of cats who need an alternative medication to methimazole. It is a dye for contrast radiography and using it for hyperthyroidism is definitely an experimental use, although there are studies to support this use. Iopanoic acid is similar to ipodate and should work about as well.

I would want to send a patient of mine who was having trouble with the oral medications for radioactive iodine therapy as soon as it could be arranged, rather than switching oral medications. This would be especially true for a patient who has had surgery with recurrent hyperthyroidism because I would think that the radioactive iodine would have the best chance of eliminating active thyroid tissue outside of the thyroid glands, such as from a malignant thyroid tumor. We have sent several cats directly for radioactive iodine therapy without giving any prior treatment with methimazole or other medications and so far, this has not caused problems for any of our patients. It is a good idea to try very hard to evaluate the kidney function prior to treatment, since that is the one thing that radioactive iodine therapy sometimes unmasks. Compensated kidney failure may worsen with the rapid decrease in thyroid hormones and alterations in blood pressure due to the changes. As long as everyone is aware of this and looking for signs, it is usually possible to get control of the kidney problems again and get back to a state in which compensated kidney failure exists rather than an acutely worsening situation. It is very good that there are no signs of this at the present time.

You and your vet are already doing the other things that I can think of, such as frequent small meals, famotidine (Pepcid AC tm) or similar medications, metoclopramide (Reglan Rx) and general nursing care. I don't have any really good alternative treatment plans for the vomiting. Given this, my instinct is to go for the radioactive iodine therapy and hope it works, which would eliminate the need for methimazole if it is the problem and would also control the hyperthyroidism better, just in case control of it is the problem, rather than the methimazole.

I hope that this helps some.

Mike Richards, DVM 9/1/2001

Heartworms in Mexico - Melarosime (Immiticide Rx)

Question: DR. RICHARDS Hi!! how are u? I hope well…… It is me, Luis from México continuing with the Rocket and Nena microfilariae treatment case. I have followed all the advices that you indicated me, they have finished the adulticide treatment receiving the third injection of immiticide on May 5, after that, i put them on a 1 month exercise limiting period, and then on a controlled exercise period, in that period i was very very worried because they get tired so easy, even with a short walk, i guess that was due for all the time (like 3 months) they were on a complete inactivity, later that, they started to have the normal life that they use to have before treatment, at this days they exercise hard on their own, and of course they get tired but i guess the normal. On June 5 (4 weeks later the third shot), they started the microfilaricide treatment receiving the monthly Heartguard Plus pill, just as on July 5 the second one, and on August 5 the third one. During this monthly medication period, there hasn´t been any bad adverse reactions or instances as you said. There are only two things that are preoccupating me, both happen with Nena, the first one is that days after ( i don´t know when exactly) the last injection, right on the injection site it came out a swelling, is like a little golf ball, and i wonder how bad could it be, and also if it is going to disappear or vanish, i see and i feel that Nena is now very sensitive at the swelling area ( i see that whan i caress her), i don´t know if it hurts. And my second preocupation, is that she is fattening a lot, i have not check her body weight but she lately looks obese, What do you thing about???? Do you think this could be done due the treatment?? What do you recommend me to do???

The last thing, in 7 days approximately (on Septmeber 5) it is gonna be four months after the adultice treatment, as you say, it is the appropiate time to recheck the blood (i still have left two idexx heartworm kits), so my question is, do i suspend the heartgard plus pills for rechecking the blood??? Do i have to recheck blood exactly on September 5????

I hope you answer me before that date, so that way i will know what to do.

Thanks a lot and receive my regards Luis

Answer: Luis-

I think it would be best to have the lump on Nena checked by your vet. It would be good to suction a sample from it with a syringe in order to see what it is. Melarsomine causes sterile abscesses in some patients and draining it could help her feel less pained by this. Less commonly, an infected abscess occurs at the site and that should be drained and antibiotics used to control the infection. It is usually possible to differentiate between these conditions by examining the material that is withdrawn, or by bacteriologic culture.

Four months is the earliest that checking to be sure that the adult worms have been killed will work. Personally, I would wait five to six months just to be a little more sure that there won't be a false positive. You should not stop the Heartgard tablets. Administering them has no effect on the occult heartworm examination.

I suspect that Nena has probably gained weight due to the inactivity and from not having an illness anymore. If you gradually increase her exercise and perhaps cut back a little on her food, that should help. The small possibility that something else is going on is another good reason to have her examined by your veterinarian, though.

Mike Richards, DVM 9/1//2001

Radioactive iodine therapy

Question: Dr. Mike, Can you please tell me your thoughts on Radioactive iodine treatments for cat with hyperthyroidism? Sorry I can not be more specific about the condition of the cat, it is not mine, a friend of mine asked if I knew ..and I do not. One of my cat's bloodwork has shown that he is on the path to this condition now, so it is something I am now interested in. Thank you for your time. Cindi

Answer: Cindi-

Radioactive iodine therapy is considered to be the best therapy for hyperthyroidism by most of the specialists who write on this condition. It is generally safer than surgery and more consistently effective than medical treatment using methimazole (Tapazole Rx). The biggest risk of using this therapy is that a cat that has pre-existing kidney failure may experience a worsening of that condition when the hyperthyroidism is totally controlled. For this reason, there is some reason to consider using methimazole for cats with known pre-existing renal failure and it is a good idea to to enough lab testing prior to this therapy to be reasonably sure that kidney failure is not currently a problem, since it will be necessary to look for subtle clues.

If I had a cat with hyperthyroidism again (I have had one, but prior to the time that this therapy was available in my area), I would have my cat treated with radioactive iodine. The initial cost is prohibitive for some people, as it is around $1000 right now in our area, not counting trips to the facilities that do it. This has been the major stumbling block for most of our clients.

Mike Richards, DVM 6/12/2001

Is there a risk of hyperkalemia in Hyperthyroid cat

Question: Hi,

I am a professional cat-nanny (cat-sitter) in the Netherlands, and I hope you can help me on my way : a cat with hypertheroid (12) was also diagnosed with hypokalemia. her thyroid is now back to normal with 2 a day carbimazol, but her potassium is still low, so she needs it to have suplemented twice a day too. Now my question: is there a risk of hyperkalemia ?

I learned once the thyroid is controlled it usually gets balanced, but hers still keeps too low. are there any other causes ? I learned that with humans it can be caused by high blood pressure too. so could that be the cats problem ? Her heart had a murmer but the vet claims it is "all of a sudden gone". The problem I run in to is that if the owner is out and I take care after her, I have no immediate control over her food intake as she lives with an obese neutered male (12) with a slight risk to develop unirany tract problems. He has been diagnosed with bladder stones ones, once being cured they went back toTechnical light diet , and they are now on Hills senior.

I could fed them Hills I/D canned while the owner is out as it has the highest potassium balance, it has the best Ph for the cat with the bladder problems and supplement her with a treat with potassium while in. yet my problems is still there , what if there is too much potassium intake ? does potassium also have a higher risk in developping urinary tract problems or is it "safe".


Answer: Lotje-

It is very difficult to cause hyperkalemia with oral supplementation. There are pretty good regulatory systems to keep the potassium level from rising too high from oral absorption. We find that it can be hard to get the potassium levels to rise sufficiently in some of our patients with kidney failure and hyperthyroidism can mask kidney failure to some degree (even when it is being treated with reasonable success) so there may be a subtle problem there that hasn't been identified. When we have this problem we give additional potassium using subcutaneous fluids that have added potassium. We haven't had any problems with hyperkalemia administering potassium in this manner, either, but we worry about it a little more when doing this. That doesn't sound like a very good option for you, though.

I am not aware of a evidence to suggest that hypertension leads to hyperthyroidism in cats but I am not sure that doesn't happen. It is very common for hyperthyroidism to cause hypertension, though. Usually successful treatment for the hyperthyroidism will control the blood pressure but sometimes we have to add medications to get the blood pressure down. It is not highly unusual for heart murmurs to develop in cats with hyperthyroidism and then for the murmur to resolve when the hyperthyroidism is controlled.

I don't think that potassium plays much of a role in the development of urinary tract infections, either good or bad. I don't think that i/d diet has enough potassium in it to be helpful for this situation, though. I think it would be best to use the regular diet the cats are used to, even if you can't get potassium supplement into the cat while its owner is away. A few days without supplementation can usually be tolerated by cats who are being given potassium without adverse effects.

I hope this helped with your questions. If not, please feel free to write for clarification.

Mike Richards, DVM 5/5/2001

Hyperthyroidism questions from Cairo

Question: Dr. Richards, Thank you for your quick response and suggestions. I was able to find carbimizole at a local pharmacy. It is dispensed in 5mg tablets. I would greatly appreciate it if you could give me the dosage for carbimizole. Once she is on this medication, what should I look for in respect to side effects? Also, should she be tested for anything to monitor kidney function, etc.?

I am going to look into finding a surgical specialist here in Cairo. My vet here did not indicate that this was an option. A surgical procedure is not always the best thing to have done in Cairo. We are usually told to have things conducted in the States (for humans). I have also had experience with some vets regarding horse care here in Egypt. There is usually a lack of equipment or medical supplies. In addition, the care given to the horses is sometimes behind that conducted in North America and Europe. The latest techniques aren't usually conducted. However, I am not going to close the door on this option. If you know of a surgical specialist here in Cairo, I would like to get their name and number.

Again, thank you for your help. I will look forward to hearing from you regarding the carbimizole dosage, possible side effects, and follow up testing.

Thank you. Kriss

Answer: Kriss-

The dosage for carbimazole is 5mg every 8 to 12 hours. The usual practice is to start off giving it three times a day, usually for a week, and then cut back to twice a day as the symptoms of hyperthyroidism disappear and the T4 level drops.

A couple of years ago someone sent lab information, including very good ultrasound images, from a veterinary hospital in Cairo. I have been unable to locate those records and may not have kept them. I have assumed that with this level of care available it was likely that other care, such as surgery, must be similarly available, at least at some practices. I wish that I was able to supply more information but I am not even sure that I had the name of the veterinary hospital originally. Hopefully, if the need arises, you will be able to find good care, though. Mike Richards, DVM 1/15/2001

Tremors in cats with Hyperthyroidism

Question: Several members of my support group, including myself, have noticed that our cats are prone to little tremors going through their bodies. I understand that this can be caused by hypocalcemia. Could this be the cause even when a blood test shows calcium levels are normal? Could the tremors be the cat's method of generating heat? I would think that a hyper-T cat who is being treated with Tapazole and is a little on the thin side could feel the cold more than a healthy cat. What would you suggest? Anne

Answer: Anne- People with hyperthyroidism sometimes have tremors and there are anecdotal reports of this problem occurring in cats. Unfortunately there are a lot of other causes of tremoring, even including agitated purring. Total calcium levels can be misleading. If you wish to try to rule out hypocalcemia with a more reliable test, if you ask for a test for ionized calcium levels, it will provide a more accurate assessment of the free calcium level, which is the active ingredient.

Cats with hyperthyroidism are probably more likely to be affected by cold, as they almost always have less body fat than cats that do not have this disease. They also tend to have higher blood pressure, especially when methimazole (Tapazole Rx) is only partially controlling the hyperthyroidism and we think tremoring occurs in patients with high blood pressure based on our clinical observations. I can't recall seeing any proof of that observation, though.

Mike Richards, DVM 1/8/2001

Hyperthyroid problems in cat

Question: Dr. Richards, I need some help with one of my cats. We currently live in Cairo, Egypt. Winnie is a 13 year old neutered female who previously did not have any health issues. Winnie (brought over from the States) has presented with symptoms of hyperthyroidism. In the past year, she has lost 1/3 of her starting weight (9 pounds down to 6). She is emaciated. I am feeding her 3 to 4 times a day. She has a voracious appetite that is never satisfied; she is restless; vomits more than usual; has constant diarrhea; and has become very vocal. She exhibits a definite behavior change. The veterinarian in Cairo tested her for T4 levels as well as another blood test. Based on the test results, he indicated that she has hyperthyroidism. His suggestion was to find information on the internet regarding the anti-thyroid medication used in the States and start her on that to see fi her T4 levels would lessen. The only anti-thyroid medication available in Cairo is propylthiouracil (PTU), which is available in 50 mg tablets. Based on my internet search, I found that Tapazole is recommended over propylthiouracil due to adverse side effects. Unfortunately, surgery and/or radioactive therapy is not an option over here. I am trying to find out the dosage for the PTU and would like to try and start her on this medication. The Cairo vet suggested that I bring back Tapazole from the States. The problem is--how do I get a veterinarian to dispense the medication without examining the cat? Do you have any suggestions? What is the PTU dosage? What should she be tested on after she is on the medication? Do you know of a veterinarian who would help us out with the medication? I am heading to the States on January 19 for ten days. I would appreciate any help that you can give me. The following are the test results.

T4 15.3 ug% (the Dr indicated that 4 would be in the normal range)

H.B. 15.3 g/dL (94.4%)

RBCs 4.9 /cmm

WBCs 10.2 /cmm

Neutrophils 48% Lymphocytes 40% Monosytes 7% Eosinophils 4% Basophiils 1% Staff 0%

Thank you for your time and assistance.


Answer: Kriss-

There is a good chance that an alternative medication, ipodate, which is a contrast agent used for making X-rays of the urinary tract is available in Egypt, although you might have to find a cooperative pharmacist to make it into an form that can be orally administered and allow accurate dosing. The usual dosage is 15 mg/kg every 12 hours.

Carbamizole (related to methimazole) is approved for use in Europe and Canada, so there is also some chance that it is available in Egypt. If so, I can try to find a dosage for you.

Propylthiouracil (PTU) has been associated with a high number of immune mediated reactions when used in cats but it would be worth trying this medication is no other medication is available. The only dosage recommendation I can find is to use 1 50 mg tablet every 8 hours "for the average sized cat".

If there is a surgical specialist in Cairo ( I think that there is, based on messages from a couple of other subscribers), removal of the thyroid gland or glands that are affected by the problem may be a worthwhile option to consider, too.

The ipodate may be the best option since it is likely to be available.

I think that you would have to visit a vet you already had a relationship with to find someone willing to dispense methimazole. It is illegal to dispense prescription medications without a client/patient/veterinarian relationship. There is a small chance that one of the mail order compounding pharmacies would be willing to honor an international prescription request (I don't know the rules pertaining to this). There are several of these online.

Good luck with this.

Mike Richards, DVM 1/9/2001

T4 levels in Cat

Question: Dr. Richards; Again, I would like to thank you for all your past information. Just a couple of questions tonight. What are the acceptable numerical levels for the "T4" thyroid blood-work? My cat had blood-work done at the end of August; "T4" was 58; more blood-work on 09/26, "T4" was 2 , More blood-work on 10/18,

"T4" was 32. Note: she was on 5mg. of 'Tapazole' twice a day, until the blood-work on 09/26. She was off the 'Tapazole' completely between the blood-work on 09/26 , and the blood-work of 10/18, when she 'clocked' in at 32. I'm to re-start her on 'Tapazole" tomorrow morning, at 2.5 mg. twice a day, and more blood-work on 11/14. Again, does all this make sense? Any patterns? Thank you again for your help. Your advise has been very helpful. Regards"


Answer: Thomas-

My first impression is that you are getting thyroid results reported in two different formats. Some labs report thyroid results in ug/dl, for which the normal range is around 1.5 to 4.5 (upper and lower values vary from lab to lab). Other labs report the values in ng/ml. The normal range for cats is about 17 to 42 ng/ml for the lab we use that reports in these values but that would vary from lab to lab, too.

So, if the laboratory is reporting in ug/dl, then a value of 32 is extremely high and would clearly warrant treatment. If the lab is reporting in ng/ml, the value would be in the normal range BUT with a history of T4 levels of 58 ng/ml and a rise in the values since discontinuation of methimasole (Tapazole, Rx), it makes sense to reinstitute therapy, anyway.

Personally, I don't worry much about T4 levels below normal when using Tapazole (Rx) unless they get really low. If the same lab was used for all samples and the value of 2 is in ng/ml, I can see why your vet wanted to discontinue the medication or lower the dosage, though.

Thyroid hormone levels vary during the day, so the time during the day the blood is drawn can have an impact in borderline cases. Thyroid hormone levels drop when there is another illness present at the same time, when corticosteroids are used and when phenobarbital is being used for seizure control. You didn't mention any of these problems but they are things to think about. The drop in total thyroxine levels (TT4) in this case is not reflective of the true thyroid status of the patient, so these factors have to be considered when evaluating the results of T4 tests.

Hope this helps some.

Mike Richards, DVM 11/6/2000

Hyperthyroidism in Siamese

Question: Dear Dr. Richards, I also have a siamese cat that is about 13 to 15 yo. She's been on Tapazol 2.5 mg. every other day for hyperthyroidism. She stills looks skinny and her heart rate appears high, she has a voracious appetite. With people B blockers are given to lessen the symptoms, can felines also be given these agents and if so, how much? thanks, James

Answer: James-

It would be a good idea to check the T4 level to see if this is an adequate dose of methimazole. This is less than it usually takes to control hyperthyroidism in cats in our practice. However, if this dose is based on checks of the T4 level, and the T4 levels are normal on the off day with this dosage, there is no need to change it.

We use amlodipine (calcium channel blocker) and enalapril (angiotensin-converting enzyme inhibitor or ACE inhibitor) in patients with hyperthyroidism and on methimazole (Tapaxole Rx) when it is necessary to control hypertension associated with it or with concurrent kidney insufficiency problems. So I think this is worth considering these if hypertension is present.

If the heart rate is over 240 bpm the use of propranolol (or other beta blocker) is warranted and may be helpful. The usual dosage is 2.5mg for small cats (less than 9 lbs) and 5mg for bigger cats, given every 8 to 12 hours, as necessary. This is sometimes done to control the heart rate prior to surgery or radioactive iodine therapy, when it seems necessary to go directly to one of these procedures, rather than temporarily controlling the hyperthyroidism with methimazole and then going on with alternative treatment.

If there are problems maintaining the T4 level in a normal range and the heart rate and/or blood pressure in normal ranges it may be better to consider radioactive iodine therapy or surgery rather than continuing with methimazole, or to consider changing the methimazole dosage.

Hope this helps.

Mike Richards, DVM 9/23/2000







Answer: Debbie-

Do you know what tests were used to test her for hyperthyroidism? These signs are just too suggestive of this disease to trust routine T4 testing if it is within normal range. Testing free T4 or doing a T3 suppression test can help to identify cats that have hyperthyroidism that isn't detectable using standard T4 level testing.

If it is possible to palpate enlarged thyroid glands, that would be another reason to consider more specific testing.

The only other possibility that I can think of would be an unidentified cancer, since diabetes is ruled out by normal sugar levels in the blood stream.

Some cats with hyperthyroidism have T4 levels that fall in the normal range for all cats --- they are just too high for the individual cat. Please ask your vet about the more specific tests, or perhaps referral to an internal medicine specialist for a second opinion, if he or she doesn't want to do the testing or isn't familiar with the tests.

Mike Richards, DVM 9/7/2000

Hyperthyroidism and Cancer

Question: Thank you for your Response. My Cat has additional blood-work done, as well as re-testing of the original blood-work, as well as a "hands-on" physical exam. I am satisfied with my Vet's original diagnois of Hyper-Thyroidism" , as well as Cancer, (But it 'bum's me out). They said they can't address the Cancer issue until the Thyroid blood levels , and Calcium levels are within manageable perimeters. We are going to start her on "Tapazole" this week , and monitor Thyroid , blood levels , calcium levels before proceeding with Cancer treatment. I was told that it would take about 6 - 8 weeks for the Tapazole to come down to accepatable levels , than proceed to Radioactive Iodine Treatment. Again does this sound feasible to you? Also, what are the side effects of Tapazole? (Can you direct me to a 'site' , maybe the Pharmacutical House that manufactures Tapazole?). Any comments, suggestions, help, advice , etc. etc. , would be greatly appreciated. I have lots more questions, I hope you don't mind. Thank you for your help, input, and advice so far.


Answer: Thomas-

I use a couple of medical formularies and the package inserts to research medications, so I don't look for links online to find information on them. However, these are the reported side effects and adverse reactions:

Methimazole (Tapazole Rx) is not well tolerated by about 20% of cats. The most common adverse reactions to it are vomiting and/or loss of appetite, which respond best to withdrawal of the medication but may clear up even if the medication is not withdrawn. The most serious reaction is bone marrow suppression leading to severe anemia, which will cause death if the medication is not withdrawn. Adverse reactions between these extremes include platelet suppression, hypersensitivity reactions (allergies to the medication), lethargy, decreased white blood cell counts, bleeding, liver damage, increased eosinophil counts and abnormal test results on immune system tests, such as the ANA test.

Due to the potential for adverse effects involving bleeding, liver damage and the immune system, it is best to be very cautious about using methimazole in a patient with a pre-existing problem with one of these conditions.

It is usually best to use methimazole for at least a month prior to surgery or radioactive iodine therapy for hyperthyroidism, which allows many patients to recover partially from heart damage, kidney damage and other systemic effects associated with hyperthyroidism. If the clinic you are dealing with wishes to have six to eight weeks of use prior to therapy, that seems reasonable to me, as long as there aren't major adverse effects prior to that time.

Tapazole (Rx) is manufactured by Lilly, if you do want to research to see if they have a web site.

We have a lot of patients on long term Tapazole therapy because their owners do not wish to pursue surgery or radioactive iodine therapy. It is often necessary to adjust the initial dosage up or down within the first few weeks in order to get the desired effect (lowering of the T4 level) without adverse effects. It is important to check for anemia during the first month of use and to call your vet and discuss any adverse reactions that you detect. Despite the potential for problems, most of our patients do well with this medication.

I can relate to worry over this drug. My own cat, Baggie, developed severe bone marrow suppression while on methimazole. So I might be more cautious about checking for anemia than a vet who hasn't had this personal experience.

Mike Richards, DVM 8/10/2000

Hyperthyroidism in older cats

Question: I took my cat (10 yr. old, female) into the vet for her annual physical (annual shots, routine annual physical , bath) , and when I went to pick her up, I was asked to agree to bring her back for additional blood-work. I asked for what , and the Doctor indicated that he wanted to test her for "Hypo-Thyroidism". I , of course, brought her in for the additional blood work. Tuesday , 07/25, I called back for the test results , and was told that she had "Hyper-Thyroidism", and also had Cancer, (which, obviously'floored' me), I asked what led to this conclusion , and he said high Calcium levels in her blood, and her increased weight gain (15.2 lbs. at last weeks physical). He was going to re-submit some testa, and also order some new ones , and I will have those results next Tuesday m 08/00. Does all this make sense? I, of course, will let you know the results of the additional tests. Tom

Answer: Tom -

Hyperthyroidism is common in older cats. Sometimes (less than 2% of cases) it is due to cancer but more often it is due to hyperplasia of the thyroid gland. So thyroid cancer is possible, but not too likely.

That means that it is a good idea to consider other possible explanations for the high calcium level. Those would include some other type of cancer (which is definitely possible), hyperparathyroidism (also a definite possibility), kidney failure (should show up in lab work) and erroneous lab results, for a multitude of reasons. In my experience, this appears to be a pretty common cause of high calcium levels, so we try not to draw many conclusions about hypercalcemia until we have two, or preferably three, sets of blood work showing consistently high calcium levels.

The most common cause of persistent hypercalcemia probably is cancer. The next most common is probably hyperparathyroidism. If the patient is being treated with medications that might increase calcium levels, such as calcitriol or calcium containing phosphate binders, calcium elevations may be due to the medications. Kidney failure usually causes hypercalcemia by causing secondary hyperparathyroidism.

I am hoping the calcium levels were an aberration and that the new lab work doesn't show this problem. Then you can just deal with the hyperthyroidism, which most vets are experienced at working with. Just to be cautious, it might be worth taking chest X-rays and carefully looking for enlarged lymph nodes and abdominal tumors by palpation (hands on exam) of the abdomen, though.

Mike Richards, DVM 8/4/2000

Possible hyperthyroidism

Question: Hi Dr Mike,

In regard to Topaz, she was diagnosed with IBD about 3-4 months ago and the vet started her on prednisone. Her main symptoms were ravenous appetite without weight gain and bulky stools with occasional diarrhea and vomiting. We started with 5 mg every day for two weeks, and reduced it to every other day. We recently increased it again to every day because she doesn't seem much better. Also, she has gone almost completely blind rather suddenly. She still wants to eat frequently, waking us up at 3:00 am to give her food. And now she has started defecating outside the litterbox. We are feeding her chicken and rice canned food, and she eats at least 2 cans per day but only weighs about 6 - 7 lbs. When she's not pacing the kitchen looking for food she sleeps in her box. The vet says the lack of activity is due to old age, as is the blindness. I've been reading about supplements and natural treatments for cats. Should I be considering any of these? Any input you can give is appreciated. I'm concerned about her quality of life and wondering if I should be considering euthanasia. She looks so thin and bony and her coat does not feel right. It pains me to see her bumping into things constantly and the poop on the floor is not much fun either. Thank you for your advice. Best regards, Andrea

Answer: On Topaz, I think that it would be a really good idea to make sure she doesn't have hyperthyroidism or diabetes. Of these two condition, hyperthyroidism sounds more likely with the signs you describe. Weight loss in a cat that is eating well, or even more than normal, is highly suggestive of hyperthyroidism. Blindness can occur as a result of high blood pressure induced by the hyperthyroidism. If the blood pressure is controlled, sight may return, but this works best if blood pressure medications are used within 48 hours of the onset of blindness. With diabetes there is initially a slight increase in appetite in many patients but then the appetite seems to drop back more towards the normal range about the time most people seek a diagnosis. Diabetes can also cause blindness because cataracts occur secondary to the diabetes. This is a more common problem in dogs than in cats but I do think it sometimes occurs in cats. In addition there is sometimes hypertension associated with diabetes, so the blindness that occurs due to high blood pressure can occur with diabetes, as well. Hyperthryoidism is a treatable illness, so it is worth finding out if it is present.

Good luck with Topaze's problems. I would recommend having her examined by your vet, if that is possible for you to manage.

Mike Richards, DVM 5/27/2000

Hyperthyroidism - feline

Q: Dear Dr. Mike: My cat Pepper, 13 yrs., has been diagnosed with hyperthyroidism but she did not show any of the signs of disease. The doctor has placed her on 3 tablets a day of Tapazola 5mg. Within two days she stopped eating/drinking and seems reluctant to do anything. She just lays on the floor and she is sort of wobbly when walking (back legs). I took her back to the vet. because it seemed she was dehydrated. I am now giving her 100cc a day of fluid. She has only been on the medication for Saturday 9/12-9/14. She is a little constipated but the doctor prescribed laclatose (I might have misspelled it) and I was giving her high fiber diet. Does the laxative stop her from absorbing nutrients into her system. I know Vitamin B & E and potassium is used up in larger quantities with hyperthyroidism but do you think I am giving her to much to soon as far as the pills are concern. I am going to see another vet on Saturday 9/19.

I am so concern because I feel I am not being probably informed of the side effects of this drug and how soon they will appear. I don't want her to get worse.

A: Dear Deborah-

I usually start my feline patients on 5mg of methimazole (Tapazole Rx) once a day. Lots of times they end up needing 15mg of the medication per day but some are stable on 5mg and most seem to require 10mg per day. My theory is that the hyperthyroidism isn't usually life threatening so if I need to adjust the dosage upwards there is time to do that later. There may be some specific reason why your vet went with a higher dosage to start with, though.

About 18% of cats (Peterson, et al, 1988) have side effects from administration of methimazole. Vomiting and loss of appetite are probably the two most common side effects. These can lead to other complications, though. The more serious side effects that occur in some cats include bone marrow suppression, thrombocytopenia (platelet deficiency) and liver disease. While these are less common they are quite serious and it is a good idea to recheck cats shortly after starting this medication and then every 3 weeks or so for at least 3 months.

I am not sure of the answer to your question concerning changes in nutrient needs and lactulose. It would not surprise me if lactulose did have some effect on electrolytes since it can cause diarrhea and does increase the acidity of the colon. I simply don't know what effects it may or may not have on vitamins. Some vets feel that administering lactulose and fiber concurrently isn't a good idea but I think the major problem with doing this is identifying which medication is actually helping.

I think it would be a really good idea to call your vet and report the signs that you are seeing. I think I'd want to do a platelet count and perhaps some serum chemistry testing to rule out liver and kidney problems associated with the methimazole. I don't recall seeing a timeframe for side effects listed in the formularies I use but my clinical experience has been that the liver problems and platelet deficiencies can occur pretty rapidly and I've seen anemia from bone marrow suppression within 10 days of administering this medication in my own cat.

I have seen several patients with no obvious clinical signs of hyperthyroidism but with enlarged thyroid glands and lab values that were high enough to make a misdiagnosis pretty unlikely.

Good luck with all of this.

Mike Richards, DVM

Hyperthyroidism possible

Q: Dr. Mike; I am writing to you because I have a not so healthy cat. He has been sick now for over 3 weeks and we do not know what to do. He started by not being talkative or playful. We realized this after a couple of days and took our 13 year old cat Sami to the vet. Our vet stated that he had lost some weight; 2.5 lbs since Dec 97' and that his urine tested high for some bacteria/ tooth infection also and gave us some pain medicine to help him. He did get back to his normal self a few days later when the vet called stating that he had hyperthyroidism and needed to take some medicine to bring his thyroid down from 11. In the interim Sami developed a case of diarrhea and not going to the bathroom in the liter box? During this development we were packing boxes to move as we were relocating so we thought it might be stress related. We waited a few days and when we saw no improvement we took him back to the vet. The vet tested his stool and said he was not producing enough digestive enzymes and had too much starch in his stool so he prescribed a powder to put on his food. We have since moved; over a week and are settled and all unpacked; Sami is still got diarrhea, doesn't appear to have put any weight back on, not going in the liter box consistently and we do not know what to do?? Our vet says that his heart sounds healthy and liver and kidneys are okay? Please can you make some suggestion? We are very informed about pancreatitis as I suffer from chronic myself. We just do not want to have to put our cat through all these different pills and surrenges of medicine that he spits back out at us and only causes him more stress in the long run. Also; his hair is feeling different. We figure that has to do with the weight loss??/

A: Brian-

Pretty much all of the symptoms you are seeing can occur with hyperthyroidism. It is a little unusual for cats to develop diarrhea but it probably can be related. Weight loss, rough haircoat, increased or decreased appetite and behavioral changes are all associated with hyperthyroidism in cats.

I am assuming that you are giving methimazole (Tapazole (Rx)) for control of the hyperthyroidism. We sometimes see reactions to this medication and if the diarrhea started after you started administering it I would be suspicious that it may be the cause. Vomiting occurs in about 10% of cats given methimazole but diarrhea must occur less frequency as it is not included in lists of significant side effects.

Methimazole tastes pretty bad. It is sometimes easier to administer if you stuff the pills into a gel cap. You can buy gel caps at many pharmacies or your vet can order them. A significant number of cats just don't tolerate methimazole well enough to use it in them. Fortunately, surgical removal of the affected thyroid gland or radioactive iodine therapy work well to control this problem, too.

Lastly, when a cat isn't eating you have to worry about hepatic lipidosis. I can't explain why but we have seen two or three cats with histories suggestive of hyperthyroidism who presented acutely with recent histories of not being willing to eat who have had hepatic lipidosis as a secondary problem to hyperthyroidism. We have been able to treat these cats more successfully than others with hepatic lipidosis, probably because the hyperthyroidism makes them more interested in resuming eating. Liver enzyme values are often normal in cats with hepatic lipidosis so a high degree of suspicion for the disorder is necessary in order to find it. If your cat still isn't eating you might want to ask your vet about the possibility that hepatic lipidosis is complicating things.

Mike Richards, DVM

Hyperthyroidism - Feline

Q: Dear Doctor,

Our beloved 14 year old, 10.5 pound tortoise has just been diagnosed with hyperthydroidism. Her level is .8. She also has a low white blood count, 3,000. I understand 6,000 to 17,000 is normal.

She is apparently in the early stages as she has not lost any weight since last year and the only reason for the test was that I noticed changes in her litterbox -- many smaller clumps, and heftier appetite and thirst levels. Our vet said he heard nothing in her heart to indicate any difficulties yet. Her kidney and liver function, according to him, are fine.

I understand that the radioactive treatment seems to be the preferred method. Unfortunately, we live in a rural area with no radioactive treatment options. We would be willing to travel if that were determined to be the best treatment. Would you have any idea where we should start investigating the radioactive treatment? We live in Northeast Nevada about four hours from Salt Lake City, Boise and Reno in different directions. We are aware that we may have to travel further than these cities, but perhaps there is one in these cities worth investigating.

Thank you.


Thank you for your time.

A: Judy-

I do not know of a veterinary hospital in the region you describe that has the capability to do radioactive iodine therapy but that does not mean that there isn't one. Your vet is probably the best source of information on this.

I was a little confused by the lab value that you reported. Without knowing what units are being reported or the lab's normal values it is hard to know if there is a misprint, but for most labs a value of 0.8 ug/dl would be low, not high. Just in case, you might want to check on this. Normal values for cats seem to range from about 1.1 to 4.2 ug/dl based on the labs we use or if the units are in nmol/L then the normals are usually around 15 to 62 nmol/L. Normal values vary from lab to lab so you have to use the normals from the testing lab the samples were sent to. If there is any question about the lab results it would be a good idea to recheck these values.

I never know what to make of a low white blood cell count in a cat or dog that is otherwise relatively normal. I get excited about wbc counts less than 3000 and your cat is right on that borderline. I don't get so excited that I do much but I do strongly encourage owners of these pets to let me check the white blood cell count again in a few days to a week or so, just to rule out lab error and weird fluctuations that don't have much to do with anything. If the red blood cell levels were also low (the hemocrit and the red blood cell count) then I'd really really want to recheck things.

Mike Richards, DVM

Hyperthyroidism and Tapazole

Q: Dear Dr. Mike - I have an 18 yr old cat who was diagnosed with hyperthyroidism 3 mos ago - he was hyperactive, eating constantly but loosing wt. ( His T-4 was 14, I think and 2 full blood panels showed no sign of kidney problems) After a mo on 5mg of Tapazole, he gained wt and T-4 dropped to 6. The dosage was increased to 10 mg and he seemed great for 2 mo. Then he seemed lethargic and hardly ate. I took hi to another vet who said the T-4 was too low, red cells down to 25, specific gravity 1.013 and BUN and creatin were now low. We cut the Tapazole back to 5mg & he immediately started eating, became active and the red cell count went back to normal. But, I am now told that he has to be on fluid therapy 2x /day for 4 days and 1x/day after that for CRF. He has had fluids for 2 days, is very stressed, miserable, not eating and lethargic again. Should I be getting another opinion? Does this sound like radical treatment? Could the new symptoms have been caused by too much Tapazole? I'm miserable too! Any guidance would be appreciated! Thank you. Kathi

A: Kathi-

It is pretty important to use fluids early in renal disease so I think that was a reasonable approach. Usually BUN and creatinine rise with renal problems, though. I would withdraw Tapazole in this circumstance since it worries me a great deal when the hematocrit (percentage of red blood cells) starts to drop but lowering the dose is probably a reasonable approach at first. This type of reaction to Tapazole is the reason that I recommend alternatives (surgery or radioactive iodine therapy) for long term control. A number of cats have reactions to Tapazole.

I hope things are improving now.

Mike Richards, DVM

Chronic Vomiting, weight loss suggestive of Hyperthyroidism

Q: Dear Doctor: I am excited to have found you! I have a 13 year old spayed, vaccinated, indoor,


Michael Richards, D.V.M. co-owns a small animal general veterinary practice in rural tidewater Virginia. Dr. Richards graduated from Iowa State University's College of Veterinary Medicine in 1979, and has been in private practice ever since. Dr. Richards has been the director of the PetCare Forum...