Is the t3 in ndt gentler than liothyronine

[AS14]

Hi

Is there a difference in the way t3 behaves between liothyronine and In ndt .

I know liothyronine is rapidly absorbed but what happens in ndt, is it a slower gentler absorption or just as rapid as liothyronine.

Thank you

[diogenes Remembering]

It could be, but as of now, the appropriate studies have not been carried out. NDT is of course desiccated thyroids of pigs or cows. The bulk of the T4 and T3 in NDT will therefore be bound onto a thyroglobulin (protein) molecule. This is how the T4 and T3 is assembled in the gland. It is only when the thyroid content leaves the organ that the T4 and T3 are released into the bloodstream from the protein by an enzyme reaction. But if you take NDT by mouth, this process may be quite a bit slower (I do not know how susceptible the complex is to stomach enzymes for example) and as you say, the availability of the T4 and T3 may be slowed up. This is unlike T4 and T3 themselves, which have rapid absorption.

[AS14 in reply to diogenes]

Thank you very much

[diogenes Remembering]

This paper investigates the removal of T4 from thyroglobulin-T4 complex. It shows that the removal of T4 by various protease (protein destroying) enzymes is rather slow and incomplete (if the enzymes are eg in the stomach). From this I would say that there is quite a bit of T4 and T3-thyroglobulin that passes the stomach and is slowly decomposed to T4 and T3.

Biochem.J.(1968)109,787

Hydrolysis of 125I-LabelledThyroglobulin by Pancreatin, Pronase and Pepsin

P.G.MALAN

Department of Biochemistry, University of Edinburgh

[jimh111]

NDT may well have slower T3 absorption and slower effects on fT3 levels, I don't know of any studies.

Medscape reference.medscape.com/drug... has this comment under Pharmacokinetics:

Time to peak

T4: 2-4 hr

T3: 2-3 days

Half-Life

T4: 6-7 days (euthyroid); 3-4 days (hyperthyroid); 9-10 (hypothyroid)

T3: 2.5 days

I don't know what they mean by 'time to peak' or whether it refers to fT3 or tT3. It seems strange that T4 peaks much quicker than T3. (could be result of T4 to T3 conversion?). Also, is this the result of a single bolus dose or daily tablets?

It does seem that T3 in NDT is more slowly released than L-T3 and this may be why some patients prefer NDT. The above data if valid provides a strong recommendation for combined NDT / levothyroxine therapy.

[AS14 in reply to jimh111]

Thank you

That helps a lot its much appreciated it.