Levothyroxine sodium anhydrous

[helvella]

Over the years we have seen several discussions around the issue of some manufacturers stating "Levothyroxine sodium" and others "Levothyroxine sodium anhydrous" .

Just noticed that the current British National Formulary gives the active ingredient in every listed levothyroxine product, including liquids, as "Levothyroxine sodium anhydrous".

bnf.nice.org.uk/medicinal-f...

I have always said that the anhydrous form is what is used to define potency. Yet, fairly obviously, it will not be anhydrous in the liquid products! Indeed, it is likely to be hydrated in the tablets by the time we swallow them.

(I suspect that the manufacturers always use the anhydrous form as their ingredient. Otherwise they have to be sure exactly what state of hydration it is in so they can measure it properly. Far easier to stick to the anhydrous form.)

[diogenes Remembering]

It's also the case that anhydrous sodium levothyroxine is hygroscopic. That is, when exposed to the atmosphere tablets will absorb water. This means that naked tablets shouldn't be left lying around for any length of time, for fear of degradation through water absorption.