DOSE-CONVERSION FROM LT4 TO ARMOUR THYROID

[helvella]

It has been said pretty much forever here (since start of this forum) that the "suggested" one grain = 100 micrograms of levothyroxine conversion is most often unacceptable.

As a rough estimate, I think many have found it closer to one grain = 75 micrograms. But, as with everything to do with thyroid, we are all individuals and this is only a rough guess.

And the issue that is almost always ignored is that if someone converts back from desiccated thyroid to levothyroxine using standard formulas, they will likely end up significantly over-dosed.

DOSE-CONVERSION FROM LT4 TO ARMOUR THYROID

Alexandra O’Sullivan1, Ronald Brazg2, Barry Horowitz3, Gary Pepper4, Hong Li5, Oscar Antunez-Flores6 , William Ferguson*1, Antonio Bianco7

1 AbbVie, Inc., USA,

2 Rainier Clinical Research Center, USA,

3 Metabolic Research Institute, Inc., USA,

4 Palm Beach Diabetes and Endocrine Specialists, P.A., USA,

5 AbbVie, Inc., USA,

6 AbbVie, Inc., USA,

7 Section of Adult and Pediatric Endocrinology and Metabolism, University of Chicago, USA

Objective: A phase 2 dose-conversion study (ARCH) which was recently completed, included an objective to develop a methodology for switching patients from LT4 to Armour Thyroid (ATH).

Methods: ARCH participants were required to be treated with LT4 for at least 12 months and have an in-range TSH (0.45–4.12 mIU/L) at screening. Participants were randomized to receive their current dose of LT4 or a prespecified dose of ATH calculated based on a dose-conversion chart (USP Drug Information 2000). The USP states that 1 grain of ATH is equivalent to 100 mcg of LT4, which led us to create a dose conversion chart of 11 doses for the ARCH study.

Results were analyzed for participants who completed the Titration Period (18-36 weeks) with an in-range TSH (Titration Responders).

Dose-conversion results were analyzed using regression best-fit to investigate the dose at the end of titration compared with the dose prior to randomization.

Results: For the LT4 participants, the slope of the regression line (the regression slope = 1.0008 [R2 = 0.8949]) was nearly identical to the slope of the identity line, indicating that most participants’ pre-randomization dose matched their post-randomization dose (70.2%); 8.3% of participants required an up-titration and 20.7% of partici- pants required a down-titration. For the ATH participants, the slope of the regression line (the regression slope = 0.0118 [R2 = 0.8249]) was greater than the slope of the identity line (y = 0.0100), indicating that many patients who were switched to ATH required titrations to a higher dose (48.6%) than that recommended by the USP; 1.8% of participants required a down-titration and 47.7% did not require titrations. Of the ATH participants not needing titrations, *78% had a pre-randomization dose of 88 mcg or lower. The difference in the titration profiles between the LT4 and ATH participants was statistically significant (p < 0.0001).

Discussion: Based on these data, it is likely that dosing of ATH using the USP 2000 guidance is sub-optimal, and may lead to underdosing of patients. The ARCH study did not meet the primary efficacy endpoint of non-inferiority of ATH compared with LT4, and this may have been significantly impacted by the initial dosing of ATH.

Afraid I could not find this actually published - it appears to be prepared for delivery at some conference under the ETC @thyroidcancer banner. This link is likely to work only for a limited time.

drive.google.com/file/d/1dp...

[tattybogle]

i'm sure i've read that peice somewhere before .. blowed if i can remember where though.

[helvella Administrator Thyroid UK in reply to tattybogle]

Be very happy if you find it and we can have a proper link.

[tattybogle in reply to helvella]

i think i remember using it in a reply to a post , and if so i will definitely have included a link ..... but i'll never be able to find which reply unless i stumble on it by accident

[Brightness14]

I agree with the 75 not 100. I always took 2.25 grains every day for years. That would equate to 225 mcg of T4. That can't be correct. When they state that 1.6 for every kilo. I weigh 63.5 kilos. That would be just over 100 mark.

Something is wrong there or is it me. I have read it but cannot remember where.

[pennyannie]

I've tried reading the above a couple of times but have given up :

What I don't understand is that if you can't convert the T4 - no dose is going to solve the problem anyway.

We also know conversion is down regulated by non optimal vitamins and minerals, inflammation, any physiological stress ( emotional or physical ) depression, dieting and ageing.

The parameters will differ patient to patient and not a constant -

i know I've passed my best before time of day - so maybe need to lay down in a dark room !

[jade_s]

I've read somewhere (maybe STTM?) that 1 grain of NDT was about the same as 25 mcg T3. If you convert using that equivalency, you come to a T3:T4 ratio of 1 : 2.375, so that would mean 1 grain ~ 60 mcg T4 (depending on the brand). [i.e.: 9 T3 * 2.375 + 38 T4 = 59.375 mcg T4].

As I've gone from levo-only to NDT to T3-only to finally a T4/T3 combination, I've found this ratio holds for me.

As they say, YMMV (your milage may vary). I'm not claiming this conversion holds true for most people, by any means.

[waveylines]

Wow based on that at 3 3/4 grains of Armour that I take....would be a massive dose of levo thyroxine. Reckon any Endo wouldn't be happy about the reversal of the conversion! 🤣I think the problem has occurred because they have overrated the potency of the T3 content!! I always think it's roughly 3xs that of T4 So 38mcg of T4 content and 3x 9mcg of T3 is = 65mcg of levo per 1, grain probably isn't far off.

It's all rather subjective though isn't it....

[BB001]

Thanks Helvella for the heads up - I've downloaded a copy. You never know when it might come in useful. Probably not for me as I'm allergic to pork and porcine NDT.

[LindaC]

I used to have a nifty little convertor - even B the Chemist was interested in it. Wish I'd stayed using Armour.