Historical dosing with desiccated thyroid

A number of people have read and mentioned old reports which refer to doses of desiccated thyroid.

One thing that is not obvious from these accounts is that the UK and the USA adopted different standards of potency. In the early twentieth century the basic means of assaying desiccated thyroid was to measure the iodine content. (The better manufacturers followed this up with tests on laboratory animals to ensure consistency of biological effect.)

The USA standardised on an iodine content of 0.2% ± 0.03%.

The UK, it appears, standardised on an iodine content of 0.1% (not sure of allowed variation but probably similar to the USA).

It looks as if the UK product was half the strength of the USA product! So, maybe, when in a UK source we see that someone was taking six grains, that would only have been equivalent to three grains of, say, Armour or Nature-Throid.

This could possibly help to explain some of the surprisingly high desiccated thyroid doses reported. Yet another confusing factor in the history of thyroid...

Please - if anyone thinks I have misinterpreted information - let me know by responses or by private message as you wish.

15 Replies

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  • Thanks for this fascinating bit of historical divergence in potency standards for UK and USA

  • Helvella, that is interesting and sort of blows the theory that patients were better medicated prior to Levothyroxine and the TSH test out of the water.

  • Not sure it is entirely blown out of the water! But I have always had a considerable degree of scepticism.

    I have also wondered whether the levothyroxine doses were quite what they seemed? We have had issues with dextrin in Teva. What other aspects of levothyroxine tablets might have left them in effect sub-potent? Was a 100 microgram tablet of, say, 1963 as potent as a good tablet today?

  • Probably potency was +/_ a greater percent than today. We had this discussion a while back when you corrected me that my information was outdated. Remember?

  • Indeed! :-)

    Even twenty or so years ago there were considerably more makes of levothyroxine. Lots of manufacturers bailed out. I wonder whether at least some did so because they realised their product could or would soon be rumbled?

  • Probably patients did better then because they were all prescribed due only to their clinical symptoms (even a trial to see if they improved).

  • We must not forget that Levo is in mcg (micrograms) and NDT is in mg (milligrams)

    so the tablets are 1000 times bigger? lol!

  • Spare, that's just the 'stuffing' so to speak. 'excipients' in pharmacy speak. Can you imagine how small a pill would be containing only 38 mcg T4 and 9 mcg T3? It would be beyond miniscule. They dilute the medication in lots of other gunk, mix it up well so it's evenly distributed throughout the mass and then pop the slurry in to the pill making machine. It's actually probably a more accurate way of making sure that pills contain what they are supposed to contain. At the same time because of the excipients being used, some people may not 'digest' them as well as others resulting in variations of absorption. That's why I think tablets like these should be chewed up by the front teeth into little pieces and then swallowed. Increase the surface area exposed to digestive fluids.

  • Desiccated thyroid is already somewhat diluted by the thyroglobulin, etc., in the original thyroid. I don't know (nor even remember seeing) the approximate hormone-to-everything-else ratio for pure desiccated thyroid.

    Some tablets such as Levoxyl (a USA levothyroxine) puff up as soon as they get wet. Wonder why they chose excipients that result in tablets that some feel need to be chewed up?

  • Rod, Synthroid doesn't puff up. It's quite hard. I've taken Eltroxin, which is not hard. The Cytomel is also not hard. Nor is the Euthyrox (Merck) from Europe.

  • Which Eltroxin was that? GSK's?

    Yes - I think of the levothyroxines of the world, it is only Levoxyl that does puff up. From memory, this started when the product had been criticised, their reformulation was to address some of the points criticised. (There are other non-thyroid medicines which strongly puff up to disperse/disintegrate.)

    However, it caused a bit of a problem when there were reports of the puffing up occurring in throats while being swallowed. Hence the very firm advice to take with a glass of water.

  • Actually, it's the Merck product from Germany that was a threat to sticking in the throat out of all the pills I've taken.

  • I meant as the pills are the same size & Levo is 1000 times concentrated it must contain 1000 times more filler than NDT.

  • A chapter in STTM2 mentions that over the years there has been many problems with variability of Batches of Synthroid..As recently as 2013 ,28000 bottles were recalled due to lower dose readings on analysis. The year before ,around 136,500 bottles were recalled due to bottle malfunctions making the tablets unstable.

  • interesting!

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