Recommended Dosage of Levothyroxine (T4)
The recommended initial dose of levothyroxine for patients with hypothyroidism is approximately 1.6 mcg/kg/day for patients under 70 years without cardiac disease or multiple comorbidities, while patients over 70 years or with cardiac disease should start with a lower dose of 25-50 mcg/day and titrate gradually. 1
Initial Dosing Based on Patient Characteristics
- For adults under 70 years without cardiac disease or multiple comorbidities, start with full replacement dose of approximately 1.6 mcg/kg/day 1, 2
- For patients over 70 years or with cardiac disease/multiple comorbidities, start with a lower dose of 25-50 mcg/day 1, 3
- For pregnant women with hypothyroidism, increase weekly dosage by 30% (take one extra dose twice per week), followed by monthly evaluation 4
Dose Adjustment and Titration
- Monitor TSH every 6-8 weeks while titrating hormone replacement 1
- Adjust dose in increments of 12.5-25 mcg based on TSH levels 5
- For patients under 70 years without cardiac disease, more aggressive titration may be appropriate (using 25 mcg increments) 1
- For patients over 70 years or with cardiac disease, use smaller increments (12.5 mcg) to avoid potential cardiac complications 1
Special Considerations
- For patients with TSH >10 mIU/L, treatment is recommended regardless of symptoms due to higher risk of progression to overt hypothyroidism (approximately 5% per year) 1
- For patients with subclinical hypothyroidism (TSH 4.5-10 mIU/L with normal free T4), treatment decisions should be individualized based on symptoms, presence of TPO antibodies, and other risk factors 1
- For women planning pregnancy, more aggressive normalization of TSH is warranted due to increased risk of adverse pregnancy outcomes 1
- For proper absorption, levothyroxine should be taken on an empty stomach, at least 30 minutes before breakfast 6
Monitoring Protocol
- Once adequately treated, repeat testing every 6-12 months or if symptoms change 1
- Free T4 can help interpret ongoing abnormal TSH levels during therapy, as TSH may take longer to normalize 1
- Target TSH should be within the reference range (0.5-4.5 mIU/L) with normal free T4 levels 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
- Avoid excessive dose increases that could lead to iatrogenic hyperthyroidism 1
- Adjusting doses too frequently before reaching steady state (should wait 6-8 weeks between adjustments) 1