I am unaware of any "formula" to calculate replacement dosage. I have been trained to start low (75 mcg) and increase as needed to push the TSH as close to zero as possible without exceeding the upper limit of normal of T4... Check TSH and T4 one month after initiating or changing dose, and increase as needed... Once stable, check TSH/T4 q 3 months x2, and if still stable, then q 6 months. I prefer to use Levoxyl since it tends to have less of a "rollercoaster effect" than Synthroid.

This a good question. The supplementation dose depends strongly on the age , weight, comorbidities and eventual pregnancy of the patient - and of course on the TSH and FT4 level. In an average patient, e.g. a 50-year-old women without chronic ischemic heart disease, 75 kg, you can start by 75 ug levothyroxine (LT4)/d in case of severe hypothyroidism. If TSH is only around 10, or if she is asthenic, you should start with 50 ug LT4/d and than gradually titrate the dose.

However, if you have a pregnant women with hypothyroidism, you must give a high dose right away (always LT4, not in combination with triiodothyronine) - it the TSH is let´s say >10, you can start by 100 (again - look at the weight).

You must be very careful in elder patients and especially in those with chronic ischemic heart disease - in such cases, you must start very, very slowly- e.g. 12,5 -25 LT4 per day for 2-3 weeks, than increase very slowly - the full dose should be achieved in e.g. three months. Anyway, old people (e.g. >75 y) should be treated only in cases of manifest hypothyroidism, you don´t care so much about values of TSH let´s say below 10.

Thanks for the comments.Would you like to put these patients on oral calcium supplement say a citrate complex/calcitrol or not?

I don´t see a need for this unless there is hypocalcemia or vitamin D deficiency.

Calcium is not indicated unless preexisting osteoporosis, hypocalcemia, etc. exists... Should be nonfactor as long as FT4 and Total T4 do not exceed upper limits of normal range.

There is some evidence that patients on longterm usage of thyroxine supplement in hypothyroidism have a tendency of developing higher degree of osteoporosis especially females from their premenopausal age as compared to normal euthyroid females from same age and I think it should be a routine to use this supplement in them in particular.

I am not aware of any way of calculating the necessery dosage. The dosage is always individualised. How many times have we seen two more or less similar patients, needing different dosages? I feel the best way is to start with a mean dosage (i prefer 100μg) and take it from there

A well taken answer but may not prove effective in younger individuals always .Serum TSH levels are to be estimated before as well as during dose titration.