Converting one medication to another should be done cautiously.  We also must recognize that a transition, or equivalent dose is virtually never going to be perfect.  So how do you convert levothyroxine to disiccated thyroid?

Armour Thyroid is probably the most common disiccated product that I have seen used.  The most common dose of Armour Thyroid I’ve seen is 60 mg daily.  The approximate conversion of levothyroxine to disscated thyroid likely lies somewhere between 75-100 mcg/day to 60 mg of the disiccated product.  USP indicates that the conversion of levothyroxine to disiccated thyroid is 100 mcg to 60 mg respectively.

Things to consider when transitioning:

1. Why are we transitioning?  Hopefully there is a good answer to this question.
2. Recognize where the patient is at in terms of their treatment of hypothyroidism.  If their TSH is elevated, we may need to get a little more aggressive with our conversion and shoot for the high end of the dosing range, possibly even above it.
3. Identify if there are other factors at play.  Levothyroxine is notorious for binding interactions.  If this patient is non-adherent or taking the levothyroxine with other medications that may interact and reduce the amount absorbed, this will obviously impact your decision and what exact dose to convert to.

Anything else you’ve seen from your practice regarding conversion of thyroid products?

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