Levothyroxine Dosing for Hypothyroidism
The recommended starting dose of levothyroxine for hypothyroidism should be 1.6 mcg/kg/day for most adults without cardiac disease, while patients >70 years or with cardiac disease should start with a lower dose of 25-50 mcg/day, with dose adjustments every 4-6 weeks based on TSH levels. 1, 2
Initial Dosing Based on Patient Characteristics
Standard Adult Dosing
- For adults <70 years without cardiac disease or multiple comorbidities, the full replacement dose of approximately 1.6 mcg/kg/day is recommended 1, 2
- This full starting dose approach in cardiac asymptomatic patients has been shown to be safe and may be more convenient and cost-effective than a low starting dose regimen 3
Special Populations Requiring Lower Initial Doses
- For patients >70 years or with cardiac disease/multiple comorbidities, start with a lower dose of 25-50 mcg/day 1, 2
- For patients at risk of atrial fibrillation or with underlying cardiac disease, a lower starting dose is essential to avoid exacerbation of cardiac symptoms 2
- Elderly patients have decreased requirements for thyroid hormone, with some patients over 60 years needing as little as 50 mcg/day or less 4
Pediatric Dosing
- Pediatric dosing is weight-based and age-dependent, ranging from 10-15 mcg/kg/day for infants 0-3 months to 1.6 mcg/kg/day for adolescents with complete growth and puberty 2
- For pediatric patients at risk for hyperactivity, start at one-fourth the recommended full replacement dosage and increase weekly by one-fourth until reaching full dose 2
Titration Schedule
Standard Titration
- Adjust dosage by 12.5-25 mcg increments every 4-6 weeks until the patient is euthyroid 1, 2
- Monitor TSH every 6-8 weeks while titrating hormone replacement 1
- Once adequately treated, repeat testing every 6-12 months or if symptoms change 1
Modified Titration for Special Populations
- For patients >70 years or with cardiac disease, use smaller increments (12.5 mcg) and titrate more slowly every 6-8 weeks 1, 2
- For pregnant patients with pre-existing hypothyroidism, increase levothyroxine dosage by 12.5-25 mcg per day and monitor TSH every 4 weeks until stable 2
Monitoring and Dose Adjustment
- The peak therapeutic effect of a given dose may not be attained for 4-6 weeks 2
- TSH is the most sensitive test for monitoring thyroid function with sensitivity >98% and specificity >92% 1
- Free T4 can help interpret ongoing abnormal TSH levels during therapy, as TSH may take longer to normalize 1
- For patients with persistent symptoms despite normalized TSH, avoid excessive dose increases that could lead to iatrogenic hyperthyroidism 1
Common Pitfalls to Avoid
- 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 1
- About 25% of patients on levothyroxine are unintentionally maintained on doses sufficient to fully suppress TSH, highlighting the importance of regular monitoring 1
- Failure to recognize transient hypothyroidism may lead to unnecessary lifelong treatment 1, 5
Special Considerations for Subclinical Hypothyroidism
- For patients with TSH >10 mIU/L, levothyroxine therapy is recommended regardless of symptoms 1, 6
- For patients with TSH between 4.5-10 mIU/L and normal free T4, routine levothyroxine treatment is not generally recommended unless the patient is symptomatic 1, 7
- For women planning pregnancy, more aggressive normalization of TSH is warranted, as subclinical hypothyroidism during pregnancy is associated with adverse outcomes 1, 6