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Treatment for this disease is simple. Give levothyroxine therapy until the patient is in a euthyroid state. Although the upper limit of normal for TSH is 5 – most experts agree that a TSH of 3 should be reached as the majority of euthyroid adults have a TSH level around 2.
It’s estimated that 80% of T4 is absorbed and levothyroxine has a half life of 7 days – making once a day dosing ideal. Remember T4 is a prohoromone and is later converted to the active T3 hormone in the peripheral tissues.
The dose of therapy is considered to be 1.6 mcg/kg/day. This is average and will definitely vary – but it may serve as a good starting point. For the average adult 100mcg/day is a good starting point. Then, you can adjust as needed.
Older patients should be started at a lower dose such as 50mcg to reduce complications (increased cardiac demand). Those with coronary heart disease should be started at 25mcg.
How patients take the medication is very important. It should be fasting one hour before breakfast. Patients should make sure they are waiting a couple hours after taking T4 before ingesting calcium PPIs, and/or iron supplements – as they interfere with levothyroxine absorption.
After starting the medication, thyroid levels should be rechecked after 6 weeks. It takes about this long to show any changes via lab testing. Symptoms, however, may begin to improve after 2-3 weeks. If the TSH remains high, then the dose should be increased and again rechecked in 6 weeks.
Once the patient is euthyroid, the TSH can be checked yearly or sooner if the patient begins to experience any symptoms.
You need to be careful not to over treat your patients as subclinical hyperthyroidism and overt hyperthyroidism increases the risk of atrial fibrillation.
Women on estrogen therapy and those who are pregnant will need higher levels of T4 therapy. Estrogen increases thyroxine-binding globulin (TBG).
Central hypothyroid treatment
Before patients are started on levothyroxine therapy, adrenal function should be checked with an ACTH stimulation test. If there is adrenal insufficiency then it’s important to give glucocorticoids while giving levothyroxine therapy so that you don’t precipitate an adrenal crisis.
Dosing is the same as in primary hypothyroidism. These patients are assessed with free T4 levels – not TSH.