What is the recommended treatment plan for a patient with hypothyroidism starting Tirosint (levothyroxine)?

Tirosint (Levothyroxine) Treatment Plan for Hypothyroidism

Initial Dosing Strategy

For most adults under 70 years without cardiac disease, start levothyroxine at the full replacement dose of approximately 1.6 mcg/kg/day to rapidly normalize thyroid function. 1

• For patients over 70 years or with cardiac disease/atrial fibrillation, start with 25-50 mcg/day and titrate gradually to avoid precipitating cardiac complications such as angina, arrhythmias, or myocardial infarction 1, 2, 3
• Elderly patients with coronary disease are at increased risk of cardiac decompensation even with therapeutic doses 1
• Levothyroxine should be taken on an empty stomach, 30-60 minutes before breakfast, for optimal absorption 3

Monitoring Protocol

Check TSH and free T4 every 6-8 weeks while titrating the dose, as this represents the time needed to reach steady state. 1, 2

• Adjust dose by 12.5-25 mcg increments based on TSH results and patient characteristics 1, 2
• Use smaller increments (12.5 mcg) for elderly patients or those with cardiac disease 1
• Target TSH should be 0.5-4.5 mIU/L with normal free T4 levels 1, 4
• Once stable, monitor TSH annually or sooner if symptoms change 1, 2

Critical Safety Considerations

Before initiating levothyroxine, rule out concurrent adrenal insufficiency, as starting thyroid hormone before corticosteroids can precipitate life-threatening adrenal crisis. 1

• This is particularly important in patients with suspected central hypothyroidism or autoimmune conditions 1
• If adrenal insufficiency is present, start physiologic dose steroids 1 week prior to thyroid hormone replacement 1

Special Populations

Pregnancy

• Pregnancy increases levothyroxine requirements by 25-50% 5, 3
• Women with pre-existing hypothyroidism should increase their weekly dosage by 30% immediately upon pregnancy confirmation (take one extra dose twice per week) 5, 3
• Monitor TSH every 4 weeks during pregnancy, targeting TSH <2.5 mIU/L in the first trimester 1
• Return to pre-pregnancy dose immediately after delivery 5

Cardiac Patients

• Start at 12.5-25 mcg/day in patients with known or suspected ischemic heart disease 3, 6
• Assess for new or worsening angina, palpitations, or arrhythmias at each follow-up 1
• Titrate slowly with smaller dose increments to avoid unmasking cardiac ischemia 6

Common Pitfalls to Avoid

Approximately 25% of patients on levothyroxine are unintentionally maintained on doses sufficient to fully suppress TSH, increasing risks for atrial fibrillation, osteoporosis, and cardiac complications. 1, 7

• Avoid adjusting doses too frequently before reaching steady state—wait 6-8 weeks between adjustments 1
• Do not treat based on a single elevated TSH value, as 30-60% normalize on repeat testing 1, 8
• Never assume hypothyroidism is permanent without reassessment—consider transient thyroiditis 1
• Avoid excessive dose increases that could lead to iatrogenic hyperthyroidism 1

Risks of Overtreatment

Even slight overdose carries significant risks, particularly in elderly and postmenopausal women. 1, 6

• TSH suppression (<0.1 mIU/L) increases risk for atrial fibrillation 5-fold in patients ≥45 years 1
• Prolonged TSH suppression increases risk for osteoporosis and fractures, especially in postmenopausal women 1, 6
• Overtreatment is associated with increased cardiovascular mortality 1
• If TSH <0.1 mIU/L, reduce dose by 25-50 mcg immediately 1

Drug Interactions

• Iron and calcium supplements reduce gastrointestinal absorption—take levothyroxine at least 4 hours apart 1
• Enzyme inducers reduce levothyroxine efficacy 8
• Recent iodine exposure (e.g., CT contrast) can transiently affect thyroid function tests 1