What is the standard treatment for hypothyroidism?

Levothyroxine for Hypothyroidism

Yes, levothyroxine is the first-line standard treatment for hypothyroidism, used to normalize thyroid-stimulating hormone (TSH) levels and restore thyroid hormone deficiency. 1, 2

Primary Indication and Mechanism

• Levothyroxine is synthetic T4 (thyroxine), chemically identical to the hormone produced by the human thyroid gland, and serves as replacement therapy for thyroid hormone deficiency 3, 4
• It is one of the world's most widely prescribed medications, treating over 99% of patients with primary hypothyroidism 4, 5
• The medication addresses the metabolic slowing caused by hypothyroidism, which manifests as fatigue (68-83% of patients), weight gain (24-59%), cognitive issues (45-48%), and menstrual irregularities (approximately 23%) 2

When to Initiate Treatment

Levothyroxine should be started immediately for:

• Overt hypothyroidism (elevated TSH with low free T4) - treatment is mandatory regardless of symptoms 1, 2
• TSH persistently >10 mIU/L - even with normal free T4, due to approximately 5% annual risk of progression to overt hypothyroidism 1
• Symptomatic patients with any degree of TSH elevation, particularly those with fatigue, weight gain, cold intolerance, or cognitive symptoms 1

Initial Dosing Strategy

For patients <70 years without cardiac disease:

• Start with full replacement dose of approximately 1.6 mcg/kg/day 1, 6, 4
• This approach is safe and more cost-effective than gradual titration in cardiac asymptomatic patients 6

For patients >70 years OR with cardiac disease/atrial fibrillation:

• Start with lower dose of 25-50 mcg/day and titrate gradually 1, 3, 2
• This prevents exacerbation of cardiac symptoms and reduces risk of arrhythmias 3

Monitoring and Dose Adjustment

• Check TSH and free T4 every 6-8 weeks during dose titration until target TSH (0.4-4.5 mIU/L) is achieved 1, 4, 2
• Once stable, monitor TSH every 6-12 months or when symptoms change 1, 7
• Adjust dose in 12.5-25 mcg increments based on current dose and patient characteristics 1
• Larger adjustments risk overtreatment, particularly in elderly or cardiac patients 1

Critical Consequences of Untreated Hypothyroidism

• Cardiovascular complications: heart failure, increased risk of cardiac events, abnormal cardiac output 2
• Metabolic effects: insulin resistance, hyperglycemia in diabetic patients, elevated LDL cholesterol 1, 2
• Reproductive health: disrupted ovulation, infertility, increased miscarriage risk 2
• Severe decompensation: myxedema coma with hypothermia, hypotension, altered mental status, and up to 30% mortality 2

Risks of Overtreatment

• Approximately 25% of patients are inadvertently maintained on doses high enough to suppress TSH completely 8, 1
• Prolonged TSH suppression increases risk for:
  • Atrial fibrillation and cardiac arrhythmias, especially in elderly patients 8, 1
  • Osteoporosis and fractures, particularly in postmenopausal women 8, 1
  • Ventricular hypertrophy and abnormal cardiac output 8
  • Increased cardiovascular mortality 1

Special Populations

Pregnancy:

• Levothyroxine should never be discontinued during pregnancy 3
• TSH should be monitored and dose adjusted, as pregnancy typically increases levothyroxine requirements 3
• Untreated maternal hypothyroidism causes spontaneous abortion, gestational hypertension, pre-eclampsia, stillbirth, premature delivery, and adverse fetal neurocognitive development 3
• Return to pre-pregnancy dose immediately after delivery 3

Patients with positive TPO antibodies:

• Higher progression risk to overt hypothyroidism (4.3% per year vs 2.6% in antibody-negative patients) 1
• Treatment warranted for TSH >10 mIU/L to prevent progression 1

Common Pitfalls to Avoid

• Never start levothyroxine before ruling out adrenal insufficiency in patients with suspected central hypothyroidism - this can precipitate adrenal crisis 1
• Do not treat based on single elevated TSH - confirm with repeat testing after 3-6 weeks, as 30-60% normalize on repeat testing 1
• Avoid adjusting doses too frequently - wait 6-8 weeks between adjustments to reach steady state 1
• Do not ignore medication interactions - many drugs affect levothyroxine absorption and metabolism, requiring dose adjustments 7

Treatment Goals

• Normalize TSH to reference range (0.4-4.5 mIU/L) 1, 4
• Resolve clinical symptoms of hypothyroidism 2
• Prevent cardiovascular, metabolic, and reproductive complications 2
• Avoid both undertreatment (persistent symptoms, cardiovascular dysfunction) and overtreatment (cardiac arrhythmias, osteoporosis) 1