The amount of Levo in a pill has to meet a target of being within 90% - 105% of the stated strength. Or is it 95% - 105% ? I have read that Synthroid aim to make their pills closer to 105% of the stated strength while other manufacturers aim to get as close to 90% or 95%. This could be a reason for the difference in other costs.
Alternatively, this paper was written by the manufacturers of Synthroid who might have been worried about losing market share to the cheaper makes.
As I understand it from years back the range was plus/minus 10% which meant it was very necessary to stick with the same brand as if going from one at the top to one at the bottom was, if taking 100 mcg almost a dose reduction of 20 mcg. This was changed in 2006 to plus/minus 5%. I picked this up years ago from Mary Shomon in the states but when I read of the change my pharmacist confirmed that was the case here as well.
In the USA, the range is 95 to 105%. In the UK, it is 90 to 105%. If your pharmacist confirmed it was the case here, he was wrong. Look at page 6 here:
For Levothyroxine Tablets BP, the potential impact of the assay (potency) limits in place at that time ( 90.0-110.0% over shelf-life) was reviewed in 2007 by the Medicines for Women’s Health Expert Advisory Group, an independent panel of experts that advise the Commission on Human Medicines. The experts were of the opinion that these limits did not pose any clinical risk to the majority of patients. Nevertheless, following consultation with manufacturers, the BP Commission tightened the control limits for assay within the BP Monograph for Levothyroxine Tablets to 90.0 to 105.0 % over shelf-life. These more stringent controls were intended to balance the need to allow for some degradation of levothyroxine during the tablet shelf-life with tighter assay limits to reduce potential variability between products / batches.
The opinion seemed to be that is wasn't important enough to do what was necessary to tighten the lower end of the range.
Trouble with these wide ranges is that they apply tablet to tablet and batch to batch - not just make to make. Even keeping to the same make, you could go from bottom to top, or top to bottom, day by day or month by month. I am sure some makers kept their products within tighter tolerances but possibly not for our benefit - just the result of their particular process.
These ranges apply throughout the life of the product up to expiry. So a tablet made at 105% could be down to 90% on expiry date.
I have read that Synthroid aim to make their pills closer to 105% of the stated strength while other manufacturers aim to get as close to 90% or 95%.
One of the changes that did occur was that in both the USA and the UK, overage was banned.
(Overage being targetting, say, 105% at the end of the production line on the assumption that they would only be 100% when taken. In itself it seems not that bad. But some manufacturers would target even higher levels at end of production line, and they could still be super-potent when received by patients. Also, this meant that tablets from A would consistently be more potent than tablets from B (except, possibly, at the extremes).
Therefore anyone changing from A to B would very likely experience a dose reduction. This then gets interpreted by patient and, sadly, naive, ignorant or greedy doctor, as B not working so well. Hence a reason to change back to A.
All manufacturers are now expected to target 100%. How well that is policed, I do not know.
Synthroid has to be that expensive to pay for the marketing (including, I submit, this paper). That marketing is required to ensure that medics and patients are frightened into starting on Synthroid and never changing.
They admit that Synthroid is more expensive in terms of the medicine itself but doing so, they claim, avoids the other costs of not taking branded Synthroid.
Thank you for drawing my attention to that helvella. That's completely different to what I read and was told! I'm assuming it was from Mary Shomon as she was my source at that time but I understood that being difficult to get an exact dose on 25, 50, 100 then it was well nigh impossible to get spot on but it never varied and nothing was mentioned re losing potency throughout shelf life. It was 2006 i was made aware of that but to be fair to the pharmacist I would probably have just asked if our tolerance had changed as well. So she probably just confirmed that it had. I know we are always told to keep medication stable etc but I was never under the impression that it lost any potency at all! Bang goes my argument for sticking not only to the same brand but only using one size tablet! So we should not be stock piling medication though I expect that is more difficult now it appears pharmacies have to take what they are given. Nothing is ever simple is it!
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