Tuesday, February 22, 2011

How Do We Treat Dogs With Hypothyroidism?

There is no cure for hypothyroidism, but it is a disease that is easily managed.

The foundation of treatment of dogs with hypothyroidism is thyroid hormone replacement therapy. In other words, we simply replace the missing hormone to restore the dog’s metabolic function back to normal.

However, it’s important that the dog receives the proper thyroid hormone supplement that is given at the appropriate dosage and at the correct intervals to best resolve all of the clinical signs of hypothyroidism.


Thyroid hormone replacement therapy: Which product do we use?
Treatment for hypothyroidism involves lifelong oral medication with levothyroxine (L-T4), a relatively inexpensive synthetic thyroid hormone supplement. These treatments have to be given by mouth, and the supplements are available both as tablets and a liquid formulation. It is important to give the medication at the same time every day (preferably twice daily), and it’s been shown that absorption is better if given on an empty stomach.



Why give L-T4 as the thyroid hormone replacement? As discussed in our last post, thyroxine (abbreviated T4, because it contains 4 iodine molecules) is the hormone produced by the thyroid gland. It is converted primarily in the liver and kidney by an enzyme (deiodinase enzyme) that removes one of the iodine molecules, thereby forming the T3 hormone, which enters the cells. Its function is to regulate the body’s metabolism.  So by giving L-T4, this will be automatically metabolized to all of the other forms of thyroid hormone made in a dog’s body.

Administering thyroid hormone replacement therapy
How and when you administer your dog's thyroid medication will have a tremendous impact on the success of the treatment.

First of all, it is extremely important that the thyroid hormone treatment not be given with food. It is best to administer thyroid medication at least 1 hour before the dog’s meal or at least 3 hours after eating. Many veterinarians are not aware of the fact that absorption of thyroid hormone from the gut is much better when the hormone is given on an empty stomach.

Thyroxine is best given twice per day, in the morning and evening, spaced about 12 hours apart. Dividing the medication into two doses ensures that the dog receives a steady state of thyroid hormone throughout the day, rather than experiencing very high levels shortly after administration and low levels later in the day when only a morning dose is given.

Although most L-T4 medication comes in pill form, there is a liquid available (Leventa; see figure above) that the company suggests just one dose per day. However, I still recommend that the liquid medication be given twice daily for the best results. If your dog is taking liquid L-T4, be sure to discuss the dosing with your veterinarian.

Monitoring the hypothyroid dog’s L-T4 dosage
Regular follow-up blood tests are vital to ensure your dog receives the accurate amount of hormone replacement therapy. Generally blood tests are rechecked approximately 4 to 8 weeks after starting medication and again as needed while the dog’s metabolism adjusts to the therapy. After that, once yearly checks are adequate to ensure that the thyroid hormone level remains in the normal range.

When taken as directed, thyroxine is extremely safe. However, it is important to make sure your dog is receiving the proper dosage based on the variables discussed above, since excessive thyroxine intake can lead to thyrotoxicosis (thyroxine overdose), a condition that needs to be promptly addressed by your veterinarian. Common signs of L-T4 overdosage include excessive thirst and urination, panting, restlessness, and pacing. If this occurs, the L-T4 needs to be stopped for a day or two and the daily dosage lowered accordingly.

Prognosis for canine hypothyroidism
With proper treatment, the long-term prognosis is excellent. However, complete resolution of clinical features of hypothyroidism may take several weeks to months in some dogs.

43 comments:

April Eliana said...

What should you do if you forget to give your dog his thyroid medication 4 hours late?
It messes up the next dose time with eating and I don't want to overdose and give the next dose at the regular time. ?

Dr. Mark E. Peterson said...

If your dog is on twice daily LT4, I'd skip this dose (the one that is 4-hrs late). On the other hand, if your dog is on once daily LT4, then I'd give it now, despite being late.

Dr. Mark E. Peterson said...

If your dog is on twice daily LT4, I'd skip this dose (the one that is 4-hrs late). On the other hand, if your dog is on once daily LT4, then I'd give it now, despite being late.

April Eliana said...

Thank you for your answer Dr. Peterson.
Should you ever supplement with T3 as well as T4? Buddy is 22 lb. just slightly overweight, Poodle/Shitzu. The situation keeps going back and forth. He was on .20 Levothyroxine in the morning and .15 at night. When his test next came back with T4 too high we decrease the Levothyroxine to .15 BID. But next time we test, his T3 is on the low side. Also, I don't really like giving a higher dose in the morning and lower at night. I can't find a pill that is free of corn and lactose in the right dose, so that is what my vet suggested. Is that okay to do?
Buddy is also on 3mg. of Prednisolone 1x in morning (compromised immune system low IgA, IgG, IgM levels, (following Dr. Plechner's protocol).But he is not my vet. The whole thing is such a delicate balance, it makes me worry. So I really appreciate your advice. Thank you so much.

Dr. Mark E. Peterson said...

Honestly, you can't really monitor thyroid replacement while on pred because that will influence all of the levels. In other words, I don't care what the levels really are on the pred, because it wouldn't reflect what is going on inside the cells.

We really never find it necessary to give T3 in dogs. Again, the T3 is likely low because of the pred.

April Eliana said...

The reason why Leventa is given only once a day is because it is a time release formula. If you gave Leventa twice a day you would be overdosing your dog.

Dr. Mark E. Peterson said...

Sorry, but you are incorrect. Leventa is not a timed release preparation. If you doubt me, then call the company (Merck Animal Health) and ask customer support.

Dr. Mark E. Peterson said...

Sorry, but you are incorrect. Leventa is not a timed release preparation. If you doubt me, then call the company (Merck Animal Health) and ask customer support.

Michelle said...

What is the normal range for a dog's Total T4 and TSH level? In the normal range, what numbers can cause symptoms of hypothyroidism? What is the best way to give thyrosin to dogs? Thank you!

Dr. Mark E. Peterson said...

Every lab would have to establish their own reference range limit for each of the thyroid hormones. So ask the lab or your vet.

Most dogs with hypothyroidism will have low T4 or free T4 and high TSH values.

FrenchMacaroon said...

My 12 year old Maltese is currently on levothyroxine supplementation due to hypothyroidism and Benazepril for an enlarged / galloping heart. Is it okay to supplement with L-carnitine to help with her heart condition? I read online that levothyroxine and L-carnitine "cancel each other" out.

Dr. Mark E. Peterson said...

Large doses of L-carnitine are sometimes used to help blunt excessive thyroid hormone action in hyperthyroidism. The action is at the cellular level and has nothing to do with LT4 absorption.

We have absolutely no evidence that normal doses of L-carnitine blunt normal thyroid action. I take L-carnitine every day and my thyroid function remains completely normal.

FrenchMacaroon said...

Thanks for responding Dr.Peterson. Hurray, Glad to hear from you that it is safe :-) Many thanks for sharing your knowledge and experience ... all the way for Singapore

Victor Vando said...

Hi Dr. Peterson
I have a 7 year old spayed Golden Retriever about 110 lbs. No signs of hypothyroidsm except the weight and borderline high hypercholesteronemia at 256 mg/dl. T4 levels are 0.9 ug/dl.
Would you start her in levothyroxine and retest T4 leves in a month? Your thoughts please.

Dr. Mark E. Peterson said...

I would never base the diagnosis on only a resting T4 value. I'd do a complete thyroid panel, including a T4, T3, free T4 by dialysis, TSH, and thyroglobulin autoantibodies. If you have it available in your area, thyroid scintigraphy is actually the best and most accurate way to diagnose hypothyroidism in dogs.

Marie1811 said...

Hello Dr.
My 7 years old dashund scratches herself since 6 months now and lost all her hair on the leg
my vet(i am from mauritius) tried cyclosphorin but it didnt work
my vet doesnt know about thyroid glands blood test as he never did that before so
today i went to have a blood test for her thyroid glands, he took blood from my dog and i brought it to a medical center for human to make it analysed as there is no veterinary clinic for dogs here.and here are the results
TSH:0.009 u/ml
T3: 0.78 nmol/L
T4:15.20 nmol/L
could you please help me with the results and tell me if it is normal or too low or too high please?
Thank you very much
marie

Dr. Mark E. Peterson said...

All of these results look normal to me, but normally we would validate the human tests for use in dogs. So these test results may not mean very much. However, hypothyroid dogs don't generally scratch so I doubt if hypothyroidism is the problem with your dog.

Greyhoundmom said...

Just wondering how the meds would affect the dog's urine pH? The vet was concerned about a high urine pH 8.2 but in monitoring think it is affected by the medication. Before we give the med the pH is 6.0 about 3 - 4 hrs later it is up to 8.0 then is back to 6.0 before we give her the next late afternoon dose. Is this something we need to be concerned about?

Dr. Mark E. Peterson said...

He has you monitoring urinary pH? I've never been asked this before and I've never really thought about it. I have no idea how or why thyroid hormone would affect urine pH. Why would you worry about the urine pH unless there were urinary tract infections or stones?

Greyhoundmom said...

The initial time he discovered the pH she did have a urinary tract infection. Antibiotics took care of it. However his concern is long term the risk of future infections or kidney stones. We have talked about trying some of the urinary tract "treats" that have cranberry to lower the pH. But we are trying to narrow down if the pH is totally due to the thyroid meds and/or her food.

Dr. Mark E. Peterson said...

Again, I know of no studies linking thyroid treatment to urinary pH.

The Zir Effect said...

Dr. Peterson... I'm wondering if you can direct me to any studies that show the bioavailability of levothyroxine given with food vs without food. My vet did not recommend dosing on an empty stomach but as we do that with humans I started dosing that way with my hypothyroid Min Pin. Her T4 levels are still not up to normal but she is doing much better.

Dr. Mark E. Peterson said...

The drug is best given on an empty stomach. See this paper:

Le Traon G1, Burgaud S, Horspool LJ. Pharmacokinetics of total thyroxine in dogs after administration of an oral solution of levothyroxine sodium. Vet Pharmacol Ther. 2008 Apr;31(2):95-101. doi: 10.1111/j.1365-2885.2007.00935.x.

Abstract
Oral L-thyroxine (L-T4) supplementation is used to replace thyroid hormone concentrations in dogs with hypothyroidism. The pharmacokinetics of L-T4 following administration of a solution (Leventa) was investigated in healthy dogs. L-T4 was absorbed fairly rapidly (t(max) 3 h). A mean bioavailability of 22% was calculated following a single oral administration of 40 microg L-T4/kg body weight. Repeated oral administration at the same dose for 14 consecutive days did not lead to any accumulation of T4 in serum. After intravenous administration of L-T4, a serum half-life of 11.6 h was calculated. Food intake concomitant with L-T4 oral administration delayed L-T4 absorption and decreased its rate and extent by about 45%. The relative bioavailability of L-T4 following administration of a tablet formulation was about 50% of that of the L-T4 solution. The pharmacokinetic properties of liquid L-T4 after oral administration support the use of a dose rate of 20 microg/kg once daily, as a starting dose for replacement therapy in dogs with hypothyroidism.

Brennan said...

This is a great post
Over a year old I know but worth a shot, my vet has my dog on both L-thyroxine and prednizone, 10 year old 120lb yellow Labrador retriever. He had an ear hematoba and this is what initially brought us to the vet, the prednisone was to try and help his ear. Then the test showed low T4 and the thyro pills to try and get him back on track that way.
He started his medication Monday evening, and has been fine, last night (Friday night) he had a very foul, very liquid stool. Is this a normal side affect? He didn't go in the house or even run to get outside, but when I told him to go outside to pee and poo, thats how it was which is quite concerning.

Also, if we are a few hours later from work and thus his prednisone and thyro pills are late to be given, what will the side affects be? What should I do in that situation? I do hope you see this as his vet is closed until Tuesday :( thanks!

Dr. Mark E. Peterson said...

Well, many problems here. First of all, you don't diagnose hypothyroidism in a dog without signs based on only a T4 determination. Prednisone will falsely lower T4 concentration, making it difficult to fine tune the dosage.

Diarrhea can also cause of falsely low T4 concentration. Neither hypothyroidism nor L-T4 supplementation would cause it.

What would I do? I'd probably stop everything and then have my dog re-evaluated next week if the problem continue. I've never heard of treating an ear hematoma with steroids... so if this were me, I'd get another opinion.

Unknown said...

My 8 yr old min pin (19 lbs) was put on .2mg of levothyroxine twice a day..its been a little over a month and his levels have all returned normal.. His bet is continuing the same dosage now... My biggest concern is his behavior.. He's completely out of it... His eyes are buggy, he just stares at nothing and he never wants to play..its turkey heartbreaking... He has also lost around 2 pounds, which I thought hypothyroidism caused weight gain.. Are these normal signs? Should I bring him to a different vet?

Dr. Mark E. Peterson said...

I'd try cutting the dose in half and see if that helps. If it doesn't within a 3-4 days, then I'd see another vet. Something else may be going on. All other illnesses tend to lower the T4 value so the diagnosis of hypothyroidism may not be correct.

Unknown said...

My lab gunner was diagnosed hypothyroid a couple of years ago. He weighs about 80 lbs and is 9 years old. He is on levothyroxine .6 mg twice a day. He can only fetch a ball for a short while then he needs to lay down and rest on his own. This evening he came inside laid down and panted for maybe 30 minutes. Next time I'll actually time it. It just doesn't seem normal. Whatever that is. I'll also need to check what the outside temp was. I'd say about 80 degrees F. What do you think?

Dr. Mark E. Peterson said...

You need to have a complete check up done by your vet, including post-pill T4 levels. It's possible that your dog is hyperthyroid from too much LT4.

Marie said...

My dog was on levothyroxine for about 3 years now, but due to having really high thyroid levels I was told to hold it for 30 days. How long after stopping med will a reduction in his thyroid levels be noted. Also, is their anything I should be monitoring during this process.

Dr. Mark E. Peterson said...

Values should fall to normal or low levels by 2-3 days.

Vanessa said...

I'm on a trip with my dog and left her levothyroxine at home. She takes .05 mg twice daily. I'll be gone for another 4 days. Is it best to find a vet and get her the medicine where I am asap, or can I wait until I get back? Thank you Dr. Peterson!

Dr. Mark E. Peterson said...

You dog should be fine without the supplement for a few days. Just start it as soon as you can.

Terrie said...

My 70 lb. dog was put on T4 0.6mg twice daily. I find it extremely inconvenient for the twice a day dosing - so I do it at one time. Her level was elevated and they decreased it to .5 twice daily -but again, I gave it daily. Her level is elevated again. She also has some elevated liver enzymes (she had a bad liver issues a few years ago after taking antifungals). Is it really that big of a deal to give it at one time? The blood work was taken 5 hours after a one tablet dose. The vet seemed pretty peeved at me but I am a pharmacist and I know that humans take it once a day and after the drug is stabilized in the blood, it shouldn't really make that much difference. Do dogs metabolize the drug in a different way?

Dr. Mark E. Peterson said...

Dogs clear the LT4 much faster (serum half-life 12 hrs vs 7 days in man).

Daniela Schroeder Tabalipa said...

Thank you for this article, Dr. Peterson.
Since my dog started her treatment, she doesn't sleep the whole night, making my life a bit difficult since I'm pregnant and have to wake up twice every night to calm her down.
There was 2 nights that I forgot to give her the evening dose (one was last night, because I was exhausted and slept at 6.30pm. Those two nights she slept like an angel. And me too!
So I was wondering if the hormones are disturbing her sleep, if I could give the daily dose at once (even though is better to split) or if I give it earlier would be helpful?
Thanks in advance!

Dr. Mark E. Peterson said...

Sounds like the dose might be too high. How much does she weigh and what's the dose?

Daniela Schroeder Tabalipa said...

She weighs 7kg now (she was 8kg when the treatment and night behavior started - her normal weight, before hypothyroidism, was 4,8kg).

She takes Forthyron 200 µg.

The last time she had blood work, on 24 of November 2016, the T4 was 3.1.
I don't know if the scale in Germany is the same you use, but between 1.0 and 4.0 is considered normal here.
Should I test her again?

Dr. Mark E. Peterson said...

I would give a dose of 100-200 ug per day. If you dog is on 200 ug twice a day, I'd cut it in half. If on 100 ug twice a day, I'd cut out the evening dose. If the medicine is working and needed and the dose is correct, we don't base the dose only on the blood test, we base that also on the dog.

Daniela Schroeder Tabalipa said...

She is on 100 ug twice a day. So I'll follow your advice and skip the evenings.
Thank you very much for your care and attention!

Dr. Mark E. Peterson said...

Clinically, your dog is showing all of the classic signs of thyroid hormone overdosage (hyperthyroidism or thyrotoxicosis). Didn't the emergency vet do any thyroid tests? If I were the vet, I'd lower the dose (probably by half). You should consider getting another opinion, since it doesn't sound like your vet understands that overdosage can even occur.

James Parsons said...

James Parsons
Thank you you for enlightening us with you wonderful article. I have been to 2 vets and neither told me about this empty stomach thing. I have a lab mix, 75 lbs. approximately 10 years old. He had $4,000 surgery for the tendon or something on his leg about 6 months ago. The hair where they shaved him did not grow back and he was diagnosed with a thyroid condition and prescribed Roxsime 0.7m twice a day. Since I read your article I follow the meal 3 hours before the pill or a pill then one hour till meal. It is difficult as he has a built in clock and drives us nuts when it's time for breakfast, dinner and night treats. Can I give him 5 small pieces of carrots and a small doggie "beef stick" with his 2nd pill of the day 3 hours after dinner? He will be going in for his blood test the first time when he runs out of his first prescription in about 5 days. Thank you so, so much.

Dr. Mark E. Peterson said...

Should be okay. Just monitor thyroid results to make sure they improve.