What is the recommended initial treatment for hypothyroidism?

Recommended Initial Treatment for Hypothyroidism

The recommended initial treatment for hypothyroidism is oral levothyroxine (T4) monotherapy, which remains the standard of care for all forms of primary and central hypothyroidism. 1, 2, 3, 4

Initial Dosing Strategy

The starting dose of levothyroxine depends critically on patient age and cardiovascular status:

Young, Healthy Patients

• Start with full replacement dose of 1.6 mcg/kg/day in young adults without cardiovascular disease 1, 4, 5
• This allows for rapid normalization of thyroid hormone levels 3

Elderly or High-Risk Patients

• Start with reduced dose of 25-50 mcg daily in elderly patients, those with known cardiovascular disease, coronary artery disease, atrial fibrillation, or long-standing severe hypothyroidism 1, 2, 4
• Lower starting doses prevent cardiac overload and arrhythmias, particularly atrial fibrillation which is the most common arrhythmia with levothyroxine overtreatment in elderly patients 2
• Gradual titration is essential in these populations to avoid cardiovascular complications 4

Critical Timing Considerations

Pregnancy

• Levothyroxine must not be discontinued during pregnancy and hypothyroidism diagnosed during pregnancy requires prompt treatment 2
• Pregnancy increases levothyroxine requirements, necessitating dose adjustments 2
• TSH monitoring should occur throughout pregnancy with dosage adjustments as needed 2
• Untreated maternal hypothyroidism increases risks of spontaneous abortion, gestational hypertension, pre-eclampsia, stillbirth, premature delivery, and adverse effects on fetal neurocognitive development 2

Congenital Hypothyroidism

• Initiate levothyroxine immediately upon diagnosis in newborns and children 2
• Rapid restoration of normal T4 is essential to prevent adverse effects on cognitive development and physical growth 2
• Monitor infants closely during the first 2 weeks for cardiac overload and arrhythmias 2

Special Consideration: Central Hypothyroidism

In patients with central (secondary/tertiary) hypothyroidism, corticosteroid replacement must be initiated BEFORE thyroid hormone replacement if central adrenal insufficiency is present 1

• Start physiologic steroid replacement (hydrocortisone ~10 mg/m², typically 15 mg AM and 5 mg at 3 PM) first 1
• Only after corticosteroids are initiated, begin levothyroxine at 1 mcg/kg 1
• This sequence prevents precipitating adrenal crisis 1

Monitoring and Dose Adjustment

• Repeat TSH and free T4 testing 6-8 weeks after initiating therapy or after any dose change 1, 3
• Target TSH range: 0.5-2.0 mIU/L for primary hypothyroidism 4
• If TSH remains above reference range, increase levothyroxine by 12.5-25 mcg 1
• Once stable, monitor annually or sooner if patient status changes 1
• In central hypothyroidism, monitor free T4 levels (not TSH) and maintain in upper half of normal range 4

Common Pitfalls to Avoid

• Do not use combination T4 + T3 therapy as initial treatment - levothyroxine monotherapy remains standard, with combination therapy only considered experimentally in select cases of persistent symptoms despite adequate T4 replacement 6
• Avoid overtreatment - associated with increased risk of atrial fibrillation and osteoporosis, particularly in elderly patients 2, 4
• Check for malabsorption and drug interactions if TSH remains elevated despite apparently adequate dosing 4
• Do not start thyroid hormone before corticosteroids in central hypothyroidism with adrenal insufficiency 1