So if you have impaired absorbrion, you may need to increase your dose of T4 by approx. 25%, especially if your body is reacted by growing nodules on your thyroid...trying to increase your own body's thyroid output maybe? Just another reason you may require a higher dose... umm shouldn't this be obvious??
I'd expect measuring the free's would pick it up? Still for some reason it helps doctors justify the increase in dose if they have a reason?
Also why its not wise to take calcium carbonate(or probably Magnesium carbonate pr any ant-acids) within at least couple of hours("advice is usually" 4 hrs for calcium supps) of your T4 thyroid meds:-)It's not only the calcium regarding calcium carbonate, but the carbonate also plays maybe a bigger part than the calcium as the carbonate may "reduce" stomach acids.
Gastric acid is required for proper absorption of oral thyroxine, according to the results of a study reported in the April 27 issue of The New England Journal of Medicine.
N Engl J Med. 2006;354:1787-1795
"Malabsorption of thyroxine has been described in patients treated with drugs that modify an acidic environment," write Marco Centanni, MD, from University La Sapienza in Latina, Italy, and colleagues. "Both H. [Helicobacter] pylori infection and treatment with proton-pump inhibitors are frequent in Western countries, and the association of thyroid diseases with atrophic gastritis has been reemphasized. The concomitant presence of such gastric disorders with thyroid diseases may lead to uncertainty about the daily dose of thyroxine and, thus, to a continuous need for care and monitoring."
The investigators determined the dose of thyroxine required to obtain a low level of thyrotropin (0.05 - 0.20 mU/L) in 248 patients with multinodular goiter. Of the 248 patients, 53 also had H. pylori–related gastritis, and 60 had atrophic gastritis of the body of the stomach, including 31 with and 29 without evidence of H. pylori infection. The comparison group consisted of 135 patients with multinodular goiter and no gastric disorders.
The investigators also prospectively studied variation in the level of serum thyrotropin in 11 patients treated with thyroxine before and after H. pylori infection, and both before and during treatment with omeprazole in 10 patients treated with thyroxine who had gastroesophageal reflux.
Compared with the reference group, patients with H. pylori–related gastritis, atrophic gastritis, or both conditions had a higher daily requirement of thyroxine by 22% to 34%. Prospective studies revealed that H. pylori infection in the 11 patients treated with thyroxine was associated with an increase in the level of serum thyrotropin (P = .002), an effect that was nearly reversed when H. pylori infection was eradicated. Similarly, in all 10 patients treated with thyroxine, omeprazole treatment was associated with an increase in the level of serum thyrotropin. This effect was reversed by a 37% increase in the thyroxine dose.
"Patients with impaired acid secretion require an increased dose of thyroxine, suggesting that normal gastric acid secretion is necessary for effective absorption of oral thyroxine," the authors write. "Although the clinical importance of these findings is fairly clear, the mechanism by which intestinal absorption of thyroxine is impaired in patients with hypochlorhydria is unknown.... Our findings indicate that patients with multinodular goiter require an increase in the dose of thyroxine if they have concomitant atrophic gastritis, chronic H. pylori infection, or both.
La Sapienza University in Rome supported this study. The authors have disclosed no relevant financial relationships.
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the old calcium carbonate research
Thyroid. 2001 Oct;11(10):967-71.
The acute effect of calcium carbonate on the intestinal absorption of levothyroxine.
Singh N, Weisler SL, Hershman JM.
Department of Endocrinology and Metabolism, Veterans Affairs Greater Los Angeles Healthcare System, California 90073, USA. Nalini.Singh@med.va.gov
To determine the acute effect of calcium, we measured levothyroxine absorption after ingestion of thyroxine (T4) with and without simultaneous ingestion of calcium (as calcium carbonate) in seven volunteers without thyroid disease. Serum total T4, total triiodothyronine (T3), free T4, and thyrotropin (TSH) levels were measured after ingestion of 1,000 microg of levothyroxine on two separate visits at 4-week intervals: (1) levothyroxine alone and (2) levothyroxine together with 2.0 g of calcium as calcium carbonate. The amount of absorbed levothyroxine was calculated as the incremental rise in serum T4 level during the first 6 hours multiplied by the volume of distribution for the hormone. When 1,000 microg of levothyroxine alone was given to subjects, the maximum average total T4 absorption was 837 microg (83.7% of the dose ingested) at 120 minutes. When levothyroxine was coadministered with 2.0 g of calcium (as calcium carbonate), the maximum average T4 absorption decreased to 579 microg (57.9% of the dose ingested) at 240 minutes. The total levothyroxine absorption over 6 hours was significantly greater with thyroxine than that with thyroxine and calcium (p = 0.02). The administration of calcium and levothyroxine in these subjects was associated with a significant reduction in the peak increment in serum total T4 (p = 0.02) and free T4 levels (p = 0.03), as well as a significant reduction in the overall increment in serum total T4 (p = 0.003), free T4 (p = 0.002), and total T3 levels (p = 0.01) over four time points (120 minutes, 240 minutes, 360 minutes, 1,440 minutes). In summary, this pharmacokinetic study in seven volunteers indicates that calcium carbonate acutely reduces T4 absorption.
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