Recommended Doses of Levothyroxine for Hypothyroidism
The standard full replacement dose of levothyroxine for hypothyroidism in adults is 1.6 mcg/kg/day, but dosing should be adjusted based on age, cardiac status, and severity of hypothyroidism. 1
Initial Dosing Recommendations
Adults
- For adults without cardiac risk factors or advanced age: 1.6 mcg/kg/day based on ideal body weight 1, 2
- For elderly patients (>70 years): Start with lower dose of 25-50 mcg/day and titrate slowly 2, 1
- For patients with cardiac disease or at risk for atrial fibrillation: Start with lower dose (less than 1.6 mcg/kg/day) and titrate more slowly every 6-8 weeks 1, 3
Pediatric Patients
- 0-3 months: 10-15 mcg/kg/day 1
- 3-6 months: 8-10 mcg/kg/day 1
- 6-12 months: 6-8 mcg/kg/day 1
- 1-5 years: 5-6 mcg/kg/day 1
- 6-12 years: 4-5 mcg/kg/day 1
12 years but growth incomplete: 2-3 mcg/kg/day 1
- Growth and puberty complete: 1.6 mcg/kg/day 1
Special Populations
Pregnancy
- Pre-existing hypothyroidism: May need to increase pre-pregnancy dose by 12.5-25 mcg/day 1
- New onset hypothyroidism (TSH ≥10 IU/L): 1.6 mcg/kg/day 1
- New onset hypothyroidism (TSH <10 IU/L): 1.0 mcg/kg/day 1
- Monitor TSH every 4-6 weeks during pregnancy and adjust dose accordingly 2, 1
Dosing Based on TSH Levels
Subclinical Hypothyroidism
- TSH 4.5-10 mIU/L and asymptomatic: Consider monitoring without treatment; repeat thyroid function tests at 6-12 month intervals 2
- TSH >10 mIU/L: Levothyroxine therapy is recommended 2
- TSH 4.5-10 mIU/L with symptoms: Consider a trial of levothyroxine with monitoring for symptomatic improvement 2
Overt Hypothyroidism
- Full replacement dose (1.6 mcg/kg/day) for most patients without risk factors 4
- A prospective randomized trial showed that starting with full replacement dose in cardiac asymptomatic patients is safe and more cost-effective than low-dose regimens 4
Dose Titration and Monitoring
- Monitor TSH 6-8 weeks after initiating therapy or changing dose 2, 1
- Adjust dose by 12.5-25 mcg increments every 4-6 weeks until euthyroidism is achieved 2, 1
- For elderly patients or those with cardiac disease: Adjust dose every 6-8 weeks in smaller increments 1
- Once stable, monitor TSH annually 5
- Target TSH within the reference range; some patients may benefit from TSH in the lower half of the reference range if symptoms persist 2
Pitfalls and Caveats
- Inadequate response to doses >300 mcg/day may indicate poor compliance, malabsorption, or drug interactions 1, 6
- Overtreatment (suppressed TSH) can increase risk for osteoporosis, fractures, and cardiac complications 2
- In central (secondary/tertiary) hypothyroidism, TSH is not reliable for monitoring; use free T4 levels in the upper half of normal range 1
- Patients with anemia or requiring doses >100 μg/day have higher risk of abnormal TSH levels 6
- Age-related decreases in levothyroxine requirements occur, particularly in men over 60 years 3
- Medication adherence is critical for treatment success; approximately 86% of patients show good adherence 6
Immune Checkpoint Inhibitor-Induced Hypothyroidism
- For mild/moderate symptoms: Standard thyroid replacement therapy with initial full dose (1.6 mcg/kg) in young, healthy patients 2
- For elderly patients or those with cardiovascular disease: Reduced initial dose of 25-50 mcg 2
- Repeat TSH and free T4 testing after 6-8 weeks and adjust dose accordingly 2
- If TSH remains elevated, increase dose by 12.5-25 mcg 2