What is the initial treatment for hypothyroidism?

Initial Treatment for Hypothyroidism

Levothyroxine monotherapy is the first-line treatment for hypothyroidism, with dosing tailored to age, cardiac status, and comorbidities. 1, 2, 3, 4

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 immediate treatment 1, 2, 3
• Measure anti-TPO antibodies to identify autoimmune etiology (Hashimoto's thyroiditis), which predicts higher progression risk and justifies treatment 1, 4
• Critical safety step: Rule out concurrent adrenal insufficiency before starting levothyroxine, as initiating thyroid hormone before corticosteroids can precipitate life-threatening adrenal crisis 1, 2

Initial Levothyroxine Dosing Strategy

For Younger Patients Without Cardiac Disease

• Start with full replacement dose of 1.6 mcg/kg/day based on ideal body weight for patients under 70 years without cardiovascular disease or multiple comorbidities 1, 2, 3, 5
• This approach rapidly normalizes thyroid function and prevents complications from prolonged hypothyroidism 1, 6

For Elderly or Cardiac Patients

• Start with a lower dose of 25-50 mcg/day for patients over 70 years, those with coronary artery disease, atrial fibrillation, or multiple comorbidities 1, 2, 7, 4, 6
• Elderly patients with underlying coronary disease are at increased risk of cardiac decompensation, angina, or arrhythmias even with therapeutic levothyroxine doses 1
• Titrate gradually upward to avoid exacerbating cardiac symptoms 2, 7

For Patients with Adrenal Insufficiency

• Always start corticosteroid replacement BEFORE thyroid hormone in patients with suspected central hypothyroidism or concurrent adrenal insufficiency 1, 2
• Initiate physiologic dose steroids at least 1 week prior to levothyroxine to prevent adrenal crisis 1

Monitoring and Dose Adjustment

• Recheck TSH and free T4 levels 6-8 weeks after starting treatment or changing dose, as this represents the time needed to reach steady state 1, 3, 4, 6
• Target TSH within the reference range of 0.5-4.5 mIU/L with normal free T4 levels 1, 4
• Adjust dose in 12.5-25 mcg increments based on patient characteristics—use smaller increments (12.5 mcg) for elderly or cardiac patients 1
• Once stable, monitor TSH annually or sooner if symptoms change 1, 3

Special Population Considerations

Pregnancy

• Pregnancy increases levothyroxine requirements by 25-50% above pre-pregnancy doses 7
• Women with hypothyroidism who become pregnant should immediately increase their weekly dosage by 30% (take one extra dose twice per week), followed by monthly TSH monitoring 7, 6
• Untreated maternal hypothyroidism is associated with spontaneous abortion, gestational hypertension, pre-eclampsia, stillbirth, premature delivery, and impaired fetal neurocognitive development 7, 4
• Return to pre-pregnancy dose immediately after delivery 7

Subclinical Hypothyroidism

• Treat with levothyroxine if TSH is persistently >10 mIU/L, regardless of symptoms, as this carries approximately 5% annual risk of progression to overt hypothyroidism 1, 4
• For TSH 4.5-10 mIU/L, treatment is reasonable if the patient is symptomatic, pregnant or planning pregnancy, or has positive anti-TPO antibodies 1, 4, 6
• Confirm elevated TSH with repeat testing after 3-6 weeks, as 30-60% of elevated TSH levels normalize spontaneously 1

Critical Pitfalls to Avoid

• Never start thyroid hormone before ruling out adrenal insufficiency in patients with suspected central hypothyroidism—this can precipitate adrenal crisis 1, 2
• Avoid using full replacement doses in elderly or cardiac patients, as this increases risk of angina, arrhythmias, and cardiac decompensation 1, 7, 4
• Do not treat based on a single elevated TSH value without confirmation, as transient elevations are common 1
• Approximately 25% of patients on levothyroxine are unintentionally maintained on doses sufficient to fully suppress TSH, increasing risks for atrial fibrillation, osteoporosis, fractures, and cardiac complications 1, 3
• Avoid overtreatment (TSH <0.1 mIU/L), which occurs in 14-21% of treated patients and significantly increases cardiovascular and bone health risks, especially in elderly patients 1, 4

Drug Interactions Requiring Dose Adjustment

• Administer levothyroxine at least 4 hours apart from calcium carbonate, iron supplements, phosphate binders, bile acid sequestrants, and ion exchange resins, as these agents bind levothyroxine and reduce absorption 7
• Proton pump inhibitors, sucralfate, and antacids may reduce levothyroxine absorption by affecting gastric acidity—monitor TSH levels appropriately 7
• Addition of levothyroxine in patients with diabetes may worsen glycemic control—carefully monitor blood glucose and adjust antidiabetic medications 7
• Levothyroxine increases response to oral anticoagulants—closely monitor coagulation tests and consider decreasing anticoagulant dose 7

Long-Term Management

• Levothyroxine is generally continued for life in patients with primary hypothyroidism 1, 3, 5
• When properly dosed, levothyroxine is safe for lifelong use—the primary risks result from overtreatment, not from the medication itself at replacement doses 1
• Ensure adequate calcium (1200 mg/day) and vitamin D (1000 units/day) intake, especially if TSH is chronically suppressed, to prevent bone demineralization 1