Article in Harmony Vol 11 Issue IV 2013 published by Lyn Mynott

Can anyone explain the article on page 8 "What's going on with our thyroid meds?" At the end of the article is a section on Anhydrous Levothyroxine Sodium "without water" and the article goes on to say it is possible that using this form can affect its stability. I am on 75 mcg 25 & 50 both by different manufacturer's the 25mcg is from MercuryPharma the 50mcg from Almus. Both meds have anhydrous levothyroxine sodium. There is a paragraph which unless you were medically trained would not understand, "For solid oral dosage forms, a growing body of evidence links the physical form and hydration state of the drug substance to its subsequent stability. Particularly once formulated, levothyroxine has a complex stabilty profile and has been reported to be sensitive to some common excipients, light, temperature, moisture, PH and environmental oxygen". This to me states that the body isn't absorbing all of the levothyroxine, can anyone explain this to me, and if anything what do I do.....Yes I have symptoms I wish I didn't have, but dont we all, we just get on with it, unless it really affects day to day life. Any help on this would be appreciated.

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6 Replies

  • Apologies, Lyn is out of the office today - feel free to drop us an email though...


  • Thyroxine sodium and levothyroxine are simply different forms of generic "synthroid". Neither is better than the other. Whichever form you take, stick with it. The bioavailability of each thyroid preparation is a little different. If you switch from one form to another, your thyroid numbers may change, and you may start to feel hypo or hyper. The actual hormonal behaviour of either form is identical otherwise. Just be careful of the dosing level.

  • Thanks for your input! :)

  • ALL UK levothyroxine medications have to declare their levothyroxine content in terms of anhydrous levothyroxine. That is a part of the official BP standard. (At least, it is explicitly stated in the draft version which is referred to in that article.)

    It looks as if the wording in some of the Patient Information Leaflets and/or Summary of Product Characteristic documents has been updated in the relatively recent past to try to make this clear. But I do not believe that the reality has changed.

    We do not know what form of levothyroxine is actually tipped into the mixer in the factory. We do not know exactly what form of levothyroxine is present in the tablets as they come off the production line. (At least one tablet declares water as an ingredient. So even if it was anhydrous when tipped in,it likely won't be at the end of the process.) Unless the companies inform us!

    This is all based on what I have read - I could be wrong!


  • Hi rod, thank you for your reply, I dont know what to think, when both 25 & 75mcg packs from different manufacturers both say anhydrous levothyroxin sodium does that mean your body doesnt receive all of the levothyroxin it should, I think I need it clarifying, but thanks again.

  • The MHRA report was actually concerned that tablets which were fine when they were made, but could dry out if left open to the air.

    Of course, the drying out would depend on how humid the room! And that will vary from day to day for most of us. The answer to this issue might be packaging - though very likely the blister packs (that are almost universal for UK levothyroxine products) might be very much better than loose fill bottles. There is also the question over use of desiccant inside bottles. That could dry out the levothyroxine.


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