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Old 10-28-2007, 10:16 PM   #1
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how long does thyroxine stay in the body

how long does thyroxine stay in the body

 
Old 10-29-2007, 05:56 AM   #2
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Re: how long does thyroxine stay in the body

hyroxine has a half life in the body of about 7 days, triiodothyronine (T3) has a half-life of about 10 hours.

 
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Old 10-29-2007, 06:04 AM   #3
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Re: how long does thyroxine stay in the body

Half life of the T4 varies depending on you and your body chemistry.. hypers eliminated it quicker.. than normals.. and hypos retain it the longest.

Pharmacokinetic Parameters of Thyroid Hormones
Hormone ***** Ratio in Thyroglobulin ***** Biologic Potency ***** t1/2 (days)
Levothyroxine (T4) *****10 - 20 ***** 1 ***** 6-7(1)
Liothyronine (T3) ***** 1 ***** 4 ***** ≤ 2
(1) 3 to 4 days in hyperthyroidism, 9 to 10 days in hypothyroidism


What does this mean.. if you are normal it takes 6-7 days after ceasation of hormone treatment to drop to 50% blood concentration after equilibrium was achieved.. then another 6-7 days to reach 25%.. and another week to reach 12.5%.. etc.

In the case of hypers.. the process is halved to 6-7 days off meds drop you to 25% and another week would throw you to 6.25% on average. Hypos retain T4 longer.. most likely as an adaptation of not having enough to begin with.. it takes ~ 10 day cycles for the depreciation of T4 by 50% of the current supplemented T4 levels.

Sincerely,
MG
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Old 10-31-2007, 12:37 AM   #4
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Re: how long does thyroxine stay in the body

Thank you very much for responding, I ran out of my thyroxine 5 days ago and couldn't get to my doctor however, I have a prescription now but didn't tell doctor that I ran out of my meds. I was starting to feel awful so wondered if I may still have some in my body. I had a thyroidectomy 3 months ago and as it is I feel as though I am not taking enough thyroxine, I am on 100mcg and 150mcg every other day. I asked for a blood test but Dr. said too soon.
Thanks again,
Joan.

 
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