Y why change formula for levothyroxine

[77barbara]

77Barbara. Under active thyroid.

My question was, why did they need to change formula of thyroxine, mine has yo you'd for years, I took it into my own hands as to dosage because up and down every few months didn't work.

[helvella Administrator]

It looks like you are asking why "thyroxine" became "levothyroxine"?

If that is your question, well it was just a change of word!

There are two forms of thyroxine - one with a left twist, the other with a right twist. Almost every time the word is used, it means the one with a left twist - and from Latin, that gets the prefix Levo. But, just occasionally, it means the one with the right twist - again from Latin, Dextro.

So, technically, we could have levothyroxine and dextrothyroxine. For absolute clarity, we should say which one we mean. Hence the change of name from thyroxine to levothyroxine. But the substance did not change at all.

For fun, we could make a single new luxury car and call it ЯЯ. Everyone knows that the real one is RR - so most of the time no-one would be confused. Just occasionally, like when you try to get spare parts or pay your road tax, it would be important to get it absolutely right. Same here. At any pharmacy, at any pharmaceutical company, in any hospital, levothyroxine would be assumed.

(Dextrothyroxine has been tried in the past but it had serious side effects. So everyone stopped using it. But the substance still has a name and could be manufactured.)

[Ellie-Louise in reply to helvella]

How did you type RR backwards?

[helvella Administrator in reply to Ellie-Louise]

It isn't actually RR backwards it is "Cyrillic Capital Letter Ya" - twice.

If you have a program such as Microsoft Word which allows you to use Unicode characters, there is probably a menu or tool to make it possible to select any character available. In Word, Insert > Symbol.

[Ellie-Louise in reply to helvella]

Thank you. I thought you were a magician. Lol

[shaws Administrator]

Do you ensure you get the same make of levothyroxine from the pharmacists when you pick it up. There are several manufacturers and each levo could be slightly different. That's why we always advise to try and get the same make each time.

If you'd like some advice on your present dose - on reading your post, it sounds as if your GP is adjusting your dose up/down due to the TSH. So I will give you some advice as we have to take our own health into our own hands. Doctors seem to be the least informed.

Request a new blood test. It has to be at the very earliest possible, fasting (you can drink water) and allow a 24 hour gap between your last dose of levothyroxine and the test and take it afterwards. This keeps the TSH at its highest as that seems to be all that the doctors look and adjust dose according to the TSH. TSH means thyroid stimulating hormone and it rises if we become hypothyroid. Unfortunately doctors also think if it goes too low we're on too much - not so.

Make an appointment. Say you've had advice from the NHS choices for help/advice and would like a Full Thyroid Function Test plus vitamins/minerals. (if he or lab wont do some you can get them from one of our two private labs).

Make the earliest possible test - even if you have to book it a few weeks ahead.

Request: TSH, T4, T3, Free T4, Free T3 and thyroid antibodies. B12, Vit D, iron, ferritin and folate.

Get a print-out from the surgery and post on a new question for comments. Make sure ranges are shown on the print-out as labs differ and so do the ranges.

[Rosierebel]

It is possibly pure coincidence or more likely a change of manufacturer, but when the wording was changed to Levothyroxin and we were all given this, I never felt quite the same. Which makes me wonder if the change of name also bring in a new manufacturer, I don't know but there was a change at that time and I slowly went downhill after that. Having tried all the different brands now including liquids, I know that different manufacturers do make a difference, both negative and positive.

[helvella Administrator in reply to Rosierebel]

You can go back to at least 1928 and find perfectly clear distinctions between l-thyroxine and d-thyroxine - for example:

Since the insoluble fraction could not be purified it was necessary to employ in turn the two isomerides of the base; in this way, using l-a-phenylethylamine there was obtained l-thyroxine having [a]21°/5461 - 3 2° and, using d-a-phenylethylamine, d-thyroxine having [a]21°/5461 + 2.97°.

ncbi.nlm.nih.gov/pmc/articl...

The fact that is common to switch between l- and levo- (or laevo-) and d- and dextro- shouldn't be viewed as anything other than changes between two conventions.

As soon as it was realised that d- and l- forms of thyroxine exist, it was necessary to qualify which form was meant.

That for so many years, so many people were happy enough to use the word thyroxine without any qualification of l-, d- or even dl-, has two interpretations. First, that almost everyone, almost all the time, actually means l-thyroxine so why bother making the distinction? Second, that those not specifying l-, d- or dl- were being imprecise and possibly even sloppy.

(d-thyroxine has been tried but was pretty well abandoned due to side effects.)

There was no change to the formulations due to change in the outer packet. From memory, it was common to see thyroxine on the card outer, and levothyroxine inside on the Patient Information Leaflet!

I fully agree that different makes have different effects.