Initial Treatment for Hypothyroidism

Levothyroxine monotherapy is the first-line treatment for hypothyroidism, with dosing tailored to patient age and cardiac status. 1, 2, 3

Diagnostic Confirmation Before Treatment

Confirm the diagnosis with both TSH and free T4 levels: elevated TSH with low free T4 indicates overt primary hypothyroidism requiring treatment 1, 4, 2
Distinguish between primary hypothyroidism (elevated TSH, low free T4) and central hypothyroidism (low/normal TSH, low free T4), as management differs 4
Critical safety step: In patients with suspected central hypothyroidism or concurrent adrenal insufficiency, ALWAYS start corticosteroid replacement BEFORE levothyroxine to prevent precipitating adrenal crisis 5, 1, 4

Start with full replacement dose of 1.6 mcg/kg/day based on ideal body weight 1, 4, 6, 7
This approach allows faster achievement of euthyroid state in patients who can tolerate it 3, 6

Start with lower dose of 25-50 mcg/day and titrate gradually upward 5, 1, 4, 3, 7
This conservative approach prevents exacerbating cardiac ischemia, angina, or arrhythmias 1, 3, 7
Elderly patients with coronary disease are at increased risk of cardiac decompensation even with therapeutic levothyroxine doses 1

Use the lower starting dose (25-50 mcg/day) for patients with significant comorbidities beyond cardiac disease 1, 4
Patients with long-standing severe hypothyroidism should also start at lower doses 3

Check TSH and free T4 levels 6-8 weeks after starting treatment or changing dose 1, 4, 2, 7
Target TSH within the reference range of 0.5-4.5 mIU/L for primary hypothyroidism 1, 3
Adjust levothyroxine dose by 12.5-25 mcg increments based on TSH results 5, 1
Once adequately treated, repeat testing every 6-12 months or if symptoms change 5, 1

Treatment is essential at any TSH elevation to prevent adverse pregnancy outcomes including preeclampsia, low birth weight, and neurodevelopmental effects 1, 3
Women with hypothyroidism who become pregnant should increase their weekly levothyroxine dosage by 30% (take one extra dose twice per week) 7
Monitor monthly during pregnancy with more aggressive TSH normalization 1

Target free T4 in the upper half of the reference range rather than using TSH for monitoring 4, 3
Evaluate other pituitary hormones, especially the hypothalamic-pituitary-adrenal axis 3

Never start thyroid hormone before ruling out and treating adrenal insufficiency in patients with suspected central hypothyroidism—this can precipitate life-threatening adrenal crisis 5, 1, 4
Avoid starting with full replacement doses in elderly or cardiac patients, as this risks cardiac decompensation 1, 3, 7
Do not use combination therapy with triiodothyronine (T3) as initial treatment—levothyroxine monotherapy remains standard 3, 7
Approximately 25% of patients are unintentionally maintained on excessive doses that suppress TSH, increasing risks for atrial fibrillation, osteoporosis, and cardiac complications 1
Avoid adjusting doses more frequently than every 6-8 weeks before reaching steady state 1

Administer levothyroxine at least 4 hours apart from phosphate binders (calcium carbonate, iron), bile acid sequestrants, and ion exchange resins that reduce absorption 8
Proton pump inhibitors, antacids, and sucralfate may reduce levothyroxine absorption by affecting gastric acidity 8
Monitor glycemic control closely in diabetic patients, as levothyroxine may worsen glycemic control and increase insulin requirements 8
Levothyroxine increases response to oral anticoagulants—monitor coagulation tests and consider decreasing anticoagulant dose 8