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Old 05-15-2002, 02:44 AM   #1
jdf jdf is offline
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question about Levoxyl

new to board and I'm here to ask a couple of questions about Levoxyl. Our dog Roxy is HypoT and takes Levoxyl (300 mcg twice daily). On May 3, we had her RX refilled and last night, about two hours after dosing, she became hyper ( insomnia, excessive panting, polydipsia). During the day yesterday, same thing about two hours after dosing. And tonight - same thing again. This period of hyper-activity lasts about an hour and a half to two hours, after which time, Roxy can relax and sleep. Does this sound like facticious hyperthyroidism?

Are there variations in potency in different lots of Levoxyl? Would it take about ten days for any increase in potency to load and become apparent? It's my understanding that peak levels of thyroid replacement meds is about two hours after dosing, is this correct?

Sorry that these many questions are in regards to a dog - I know this is a human health board but when my dog can't sleep, I don't sleep either and I'd like to figure out what's going on so I could get some Z's. Thanks for any ideas and response. jdf

 
Old 05-15-2002, 09:33 AM   #2
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Re: question about Levoxyl

Welcome, jdf. You're from my home town! No need to apologize for asking questions about a dog. Thyroid disease is apparently quite common in pets -- cats have a tendency toward hyperthyroidism as they age (typically noted after weight loss in the animal).

Roxy must be a large dog if her dose is 300 mcg. I don't know the mechanics of how dogs absorb or metabolize thyroid meds, but I believe the average dose for a normal-sized hypo human tends to be around 125-200 mcg (although we all differ in our needs). One of the pet websites I found says that the typical dosage for a dog is 1 mcg/10 pounds twice per day as the initial dosage, with follow-up blood tests to see how that works for the patient. So it sounds to me like this dosage may be excessive. Could it be 30 mcg and not 300? By the above logic, 30 mcg would be appropriate for a 150-pound dog.

I know that Levoxyl recently (in the past few months) changed their formula but, since your prescription is so new, this shouldn't matter in Roxy's case. Here's an article about the reformulation:
<A HREF="http://thyroid.about.com/library/weekly/aa022602a.htm" TARGET=_blank>http://thyroid.about.com/library/weekly/aa022602a.htm</A>


For a human, it typically takes 4-6 weeks to fully assimilate a dosage adjustment so our follow-up blood tests are usually about 2 months following the prescription. During this time, we can have symptoms that are Hypo, Hyper or a combination of both. I would assume it is the same with dogs.


Here are a couple of canine thyroid links I found that may be helpful, but there were a ton more if you do a search on Google. (I typed in "thyroid dog.") Apparently, the most common cause of hypothyroidism in dogs is autoimmune thyroiditis (Hashimoto's):

<A HREF="http://www.canismajor.com/dog/thyroid.html" TARGET=_blank>http://www.canismajor.com/dog/thyroid.html</A> <A HREF="http://www.showdog-magazine.com/autoimmuneThyroid.htm" TARGET=_blank>http://www.showdog-magazine.com/autoimmuneThyroid.htm</A>


I don't know how high a dosage must be to produce facticious hyperthyroidism (a toxic condition), nor if it would present from only two weeks of ingestion, but I'm not a doctor. But, from what I read about it, you could ask your Vet for a Thyroglobulin blood test (along with the other thyroid blood tests) when you next go back, as Thyroglobulin levels are typically low or undetectable in facticious hyperthyroidism.

I don't know of variations in potency in different lots of Levoxyl. Levoxyl is one of the few forms of T4 med that is approved by the FDA, though it may be inappropriate to assume that this status is an indication of consistency. Others on this Board may be more knowledgeable on this subject.

I believe you are correct that the peak levels of thyroid med absorption is achieved about two hours after dosing.


I think, if you haven't yet done so, you should call the Vet and discuss your concerns. Ask about the dosage and how your dog's behaviour might indicate if it is too high or too low. (The Show Dog Magazine link above includes symptoms lists.) And let us know what happens. Hope Roxy feels better soon.

 
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Old 05-15-2002, 12:07 PM   #3
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Re: question about Levoxyl

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by ArtfulD:
<B>Roxy must be a large dog if her dose is 300 mcg. I don't know the mechanics of how dogs absorb or metabolize thyroid meds, but I believe the average dose for a normal-sized hypo human tends to be around 125-200 mcg (although we all differ in our needs). One of the pet websites I found says that the typical dosage for a dog is 1 mcg/10 pounds twice per day as the initial dosage, with follow-up blood tests to see how that works for the patient. So it sounds to me like this dosage may be excessive. Could it be 30 mcg and not 300? By the above logic, 30 mcg would be appropriate for a 150-pound dog.</B><HR></BLOCKQUOTE>

Much like the recommendation that humans start on a 25-50mcg dose, this is a very low and conservative starting point. Dogs have a much faster metabolism than humans. A friend on another message board has a medioum sized dog that requires 1200mcg (that is NOT a typo) a day to stay healthy, and according to some sources, this is not uncommon.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>
For a human, it typically takes 4-6 weeks to fully assimilate a dosage adjustment so our follow-up blood tests are usually about 2 months following the prescription. During this time, we can have symptoms that are Hypo, Hyper or a combination of both. I would assume it is the same with dogs.<HR></BLOCKQUOTE>

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Would it take about ten days for any increase in potency to load and become apparent? It's my understanding that peak levels of thyroid replacement meds is about two hours after dosing, is this correct?<HR></BLOCKQUOTE>

Since their metabolism is faster, they stabilize their doses much faster, too, though I don't know the time frame or the half-life of thyroxine in a dog's body. Correspondingly, dogs will react to a dose change more quickly and recover from it more quickly, too.

I wonder if the previous refill was the old version of Levoxyl (pre reformulation) and the newer prescription is the reformulated one and is being absorbed faster and more completely, and thus the problem.

Like Artful said, I would think that blood tests to verify what the levels are would be judicious at this point. It could be that the dose s being assimilated better, or it could be that the dose requirement has changed--that happens to humans, too.

 
Old 05-15-2002, 12:21 PM   #4
jdf jdf is offline
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Re: question about Levoxyl

Thanks, ArtfulD and Meep. Roxy weighs 65 pounds. She's been doing well up until two days ago when the insomnia started ( she's been taking Levoxyl for about two years). Went through this once before with her when we first started dosing her and a re-check indicated the dosage was too high. Since we haven't changed the dosage in quite awhile, it could very well be related to the reformulation of Levoxyl. We have a call into our vet so hopefully this can be brought under control quickly. Roxy is a paraplegic German Shorthaired Pointer and because she's disabled, we have our vet come to our home - sometimes it takes a little time to get him here.

Thanks to both of you for your insight and suggestions -
this is a great board and it's good to get such quick response. BTW ArtfulD, does your handle mean that you are an artist? I am an artist, an abstract formalist painter - just curious....Jim

 
Old 05-15-2002, 01:10 PM   #5
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Re: question about Levoxyl

Naw, not an artist, though I am married to one (photographer & pointalist). We can't advertise on this Board (so I won't ask if you have a website), but I love your style of work. Good for you for using your talent, Jim! And, Meep, I'm so glad you posted all those details.

 
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