Kabachi and Jackson derived equations for determining the optimal daily oral dose of levothyroxine based on the serum thyrotropin (TSH) concentration in a patient with primary hypothyroidism. This can provide a useful starting point from which adjustments can be made in the maintenance dose. The authors are from the Veterans Affairs Medical Center in Phoenix and University of Arizona in Tucson.



(1) serum thyrotropin (TSH) concentration in mU/L

(2) oral daily dose of levothyroxine (LT4) in micrograms per day


Logarithmic equation:


oral dose of levothyroxine in micrograms per day =

= (68 * LN(serum TSH in mU/L)) - 127


Two linear equations that approximate the logarithmic function:

Serum TSH

Oral Daily Dose of Levothyroxine in micrograms/day

< 36 mU/L

(4.1 * (serum TSH in mU/L)) - 14

>= 36 mU/L

(0.69 * (serum TSH in mU/L)) + 107


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