Maggi wrote:
> I noticed on the new Forest Pharm./Armour website that they say 90mg of
> Armour is eq. to 150 mcg of a particular T4 med as in Levothroid.  Yet, the
> conversion chart I have from Joan says that 90 mg of Armour is the same as
> 111mcg of T4.  I switched from 90mg of Armour to 75 T4 and 30 armour.
~~~~~~~

Something's fishy.  It doesn't compute.  Let's do the math.  From their own
material http://www.armourthyroid.com/faq.html#q5:

Thyroid 1 grain = 38 mcg T4
Thyroid 1 grain =  9 mcg T3

Ratio of T4 to T3 equals  4.22:1

"T3 liothyronine is approximately four times as potent as T4 levothyroxine
on a microgram for microgram basis."

They also say:
~~~~~~~
The basic "rule of thumb" in converting thyroid doses is that 100 mcg of T4
is roughly equivalent to 25 mcg of T3, or 1 grain (60 mg) of desiccated
thyroid (Armour Thyroid), or Liotrix-1 (Thyrolar-1).

Approx. Dose Equivalent:
1 grain        (60 mg) Armour = 100 mcg ( .1 mg) T4
1 1/2 grains (90 mg) Armour = 150 mcg (.15 mg) T4

 ?????  They are multiplying the EQUIVALENT VALUE of 1 grain in total and
arriving at .150 mg instead of using individual T3 component values as
below.  The equivalent value of T3 will change for each variation in grain.

i.e.  when increasing from 1 grain to 1.5 grains Armour the new values
become:
             T4         38 x 1.5 = 57 mcg T4
             T3      9 x 4 x 1.5 = 54 mcg equivalent
       TOTAL T4 equivalent = 111 mcg
~~~~~~~~
OR to put it another way:

       We know T3 has 4 times the activity of T4.  Therefore:

       1 grain (60 mg) contains 9 mcg T3 - then T4 equiv is 4 X 9 = 36
       1 grain (60 mg) contains 38 mcg T4 - then T4                   = 38

TOTAL       1 grain    (60 mg) contains 36 + 38 =   74 mcg T4 equivalent
Thus         1.5 grain  (90 mg) contains 74 X 1.5 = 111 mcg T4 equivalent
~~~~~~~~~

Maggi, in my opinion you would now be getting
                                    T4 =   75 mcg
          plus from Armour  T4 =   19 mcg
            and T3 - 4.5 mcg x 4 =   18 mcg  T4 equiv
           TOTAL T4 equivalent =  112 mcg T4 equiv

You were on 111 mcg equivalent at 90 mg Armour
You are now 112 mcg equivalent using T4 plus 1/2 grain Armour.

I don't know what the math on the website means, but the above the values
Doc Don and I have been using for calculations.  Any mathematicians out
there that can shed more light on this?

Joan McPhee, not an M.D.
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