What is the initial treatment for hypothyroidism?

Initial Treatment for Hypothyroidism

The initial treatment for hypothyroidism is levothyroxine (T4) therapy, which should be started for all patients with TSH persistently >10 mIU/L or for symptomatic patients with any degree of TSH elevation. 1

Diagnosis and Assessment

• Hypothyroidism is diagnosed biochemically with elevated TSH and low free T4 levels indicating overt primary hypothyroidism 2
• Before initiating treatment, confirm elevated TSH with repeat testing after 3-6 weeks, as 30-60% of high TSH levels normalize on repeat testing 1
• Measure both TSH and free T4 to distinguish between subclinical hypothyroidism (normal free T4) and overt hypothyroidism (low free T4) 1

Treatment Algorithm Based on TSH Levels

Overt Hypothyroidism

• Initiate levothyroxine therapy for all patients with low free T4 and elevated TSH, as this represents overt hypothyroidism requiring treatment 1, 2
• Untreated overt hypothyroidism can lead to serious complications including heart failure, myxedema coma, and decreased quality of life 2

Subclinical Hypothyroidism

• For patients with TSH >10 mIU/L and normal free T4, initiate levothyroxine therapy regardless of symptoms 1
• For patients with TSH between 4.5-10 mIU/L and normal free T4, treatment decisions should be individualized based on symptoms, presence of TPO antibodies, and risk factors 1

Levothyroxine Dosing Guidelines

• For patients <70 years without cardiac disease or multiple comorbidities, start with full replacement dose of approximately 1.6 mcg/kg/day 1, 3
• For patients >70 years or with cardiac disease/multiple comorbidities, start with a lower dose of 25-50 mcg/day and titrate gradually 1, 4
• Young adults typically start at about 1.5 mcg/kg per day, taken on an empty stomach 5
• Elderly patients and those with coronary artery disease should start at a lower dose: 12.5 to 50 mcg per day 5

Dose Adjustments and Monitoring

• Monitor TSH every 6-8 weeks while titrating hormone replacement until TSH normalizes 1, 2
• Once adequately treated, repeat testing every 6-12 months or if symptoms change 1
• Dose adjustment should only be considered after 6-12 weeks, given the long half-life of levothyroxine 5
• The recommended increment for dose adjustment is 12.5-25 µg based on the patient's current dose 1

Special Considerations

Pregnancy

• Women with hypothyroidism who become pregnant should increase their weekly dosage by 30% (take one extra dose twice per week), followed by monthly monitoring 3
• Untreated maternal hypothyroidism during pregnancy is associated with higher rates of complications, including spontaneous abortion, gestational hypertension, pre-eclampsia, stillbirth, and premature delivery 6

Elderly Patients

• For elderly patients, the risk of overtreatment is significant and can lead to atrial fibrillation and other cardiac arrhythmias 6, 7
• Start with lower doses (25-50 mcg/day) and titrate more slowly in elderly patients 1, 5

Common Pitfalls and Considerations

• Undertreatment risks include persistent hypothyroid symptoms, adverse effects on cardiovascular function, lipid metabolism, and quality of life 1
• Overtreatment with levothyroxine can lead to iatrogenic hyperthyroidism, increasing risk for osteoporosis, fractures, abnormal cardiac output, and ventricular hypertrophy 4, 1
• About 25% of patients on levothyroxine are unintentionally maintained on doses sufficient to fully suppress TSH, highlighting the importance of regular monitoring 1
• Certain drugs, such as iron and calcium supplements, reduce the gastrointestinal absorption of levothyroxine and should be taken at least 4 hours apart 5, 8
• Development of low TSH on therapy suggests overtreatment or recovery of thyroid function; dose should be reduced or discontinued with close follow-up 1
• Hashimoto's thyroiditis (chronic autoimmune thyroiditis) is the most common cause of primary hypothyroidism in iodine-sufficient areas, affecting up to 85% of patients with hypothyroidism 2