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Miss Shapes
Photo taken 13 October 2010

You’d think I was trying to play Collect-’em-All! with thyroid panel numbers from as many national laboratories as I could access. This latest one comes from IDEXX Laboratories, now that we’ve switched vets and they use a different system. For the blood tests they ran last week, this is what we got:

Free T4 (equilibrium dialysis) (ng/dL): 3.1000 (adult reference range 0.7 – 3.7 ng/dL)
Free T4 (equilibrium dialysis) (pmol/L): 39.9000 (reference range 9.0 – 47.4 pmol/L)
T4: 2.9000 (reference range, 0.9 – 3.9 ug/dL)
Interpretive Ranges: < 0.9 Low; 0.9 – 3.9 Normal; > 3.9 High; 2.1 – 5.4 Therapeutic

Dogs with no clinical signs of hypothyroidism and results within the normal reference range are likely euthyroid. Dogs with low T4 concentrations may be hypothyroid or “euthyroid sick.” Occasionally, hypothyroid dogs can have T4 concentrations that are low normal. Dogs with clinical signs of hypothyroidism and low or low normal T4 concentrations may be evaluated further by sumission of free T4 and canine TSH. A high T4 concentration in a clinically normal dog is likely variation of normal; however elevations my occur secondary to thyroid autoantibodies or rarely thyroid neoplasia. For dogs on thyroid supplement, acceptable 4 – 6 hour post pill total T4 concentrations generally fall within the higher end or slightly above the reference range.

This blood was drawn about six hours after his morning pill, six weeks into his thyroid supplement treatment. As Dr. Dodds mentioned in her test results, “Optimal therapeutic response should be in the upper 1/3rd to 25% above the upper limits of the resting optimal ranges at 4 – 6 hours post-BID thyroid medication.” So it seems that his numbers fall within acceptable range, though I was expecting a dosage adjustment since he remains so itchy. Approximately 50% of all dogs require a dosage adjustment after the second blood draw, according to one study I read.

Nevertheless, it was good to confirm that the hormone supplementation was working as it should, and that we could go ahead and order an entire bottle of Soloxine now that we knew the appropriate dosage. Once again, I placed an order with 1-800-PetMeds; my order was filled and shipped within 24 hours, thanks to the fact that the new vet was willing to fax the prescription, just like that!

Image from Drugs.com

Hello, little yellow label! Are we going to become good friends over the next several years?

One thing disappoints me is that the product information posted on Soloxine‘s own website offers no warning of the chemical properties of Levothyroxine sodium. The package insert PDF file, accessible at the above link, states that “Soloxine tablets may be administered orally or placed in the food.” Since these instructions come from Virbac themselves, I can’t exactly fault my previous vet for giving me inaccurate instructions. Could it be that the manufacturers of this drug are not aware of how thyroxine binds to soy and calcium? Or do they know something about canine absorption that magically nullifies the chemical property of this drug? Regardless, to be on the safe side, we’ve been giving Bowdu his pills one hour before or three hours after meals, on an empty stomach. At any rate, I intend to contact Virbac and ask, but I will have to make a phone call to follow up on this, since they do not post an e-mail contact.

One more thing on the Soloxine website — there’s a cheesily produced episode of a “People and Pets” show where they briefly discuss [rather, advertise] the use of Soloxine in the treatment of canine hypothyroidism. The vet on the show recommends retesting blood to ensure correct dosage two to three times a year. Given how traumatic every blood draw has been for Bowdu, this seems completely excessive. I hope we can stick to a schedule of annual blood tests at the most, if we have any say in the matter!