From the FDA Drug Label
The recommended starting daily dosage of levothyroxine sodium tablets in adults with primary, secondary, or tertiary hypothyroidism is based on age and comorbid cardiac conditions, as described in Table 1 For patients at risk of atrial fibrillation or patients with underlying cardiac disease, start with a lower dosage and titrate the dosage more slowly to avoid exacerbation of cardiac symptoms. Full replacement dose is 1.6 mcg/kg/day. The recommended starting daily dosage of levothyroxine sodium tablets in pediatric patients with primary, secondary, or tertiary hypothyroidism is based on body weight and changes with age as described in Table 2 Age Starting Daily Dosage Per Kg Body Weight* 0 to 3 months 10 to 15 mcg/kg/day
The levothyroxine treatment per lb is as follows:
- For adults, the full replacement dose is 1.6 mcg/kg/day.
- For pediatric patients, the dosage varies by age:
- 0 to 3 months: 10 to 15 mcg/kg/day
- 3 to 6 months: 8 to 10 mcg/kg/day
- 6 to 12 months: 6 to 8 mcg/kg/day
- 1 to 5 years: 5 to 6 mcg/kg/day
- 6 to 12 years: 4 to 5 mcg/kg/day
- Greater than 12 years but growth and puberty incomplete: 2 to 3 mcg/kg/day
- Growth and puberty complete: 1.6 mcg/kg/day 1
From the Research
Levothyroxine treatment should be initiated at a dose of approximately 1.6 micrograms per kilogram of body weight daily, which translates to about 0.7 micrograms per pound, with adjustments based on thyroid function tests, particularly TSH levels, as indicated by 2. When considering levothyroxine treatment per pound, it's essential to recognize that dosing should be individualized. The standard starting dose for adults is about 1.6 micrograms per kilogram of body weight daily, which is roughly 0.7 micrograms per pound. For example, a 150-pound adult would typically start with around 100-112 micrograms daily. However, this can vary, especially in pediatric populations, where the dose may need to be adjusted based on age, weight, and the underlying condition causing hypothyroidism, as noted in 3 and 4.
Key considerations in levothyroxine dosing include:
- Starting dose: Typically around 1.6 micrograms/kg/day or 0.7 micrograms/pound/day for adults, but this can vary, especially in children, where the dose might be higher per kilogram of body weight, as seen in 5 and 6.
- Adjustments: Dose adjustments should be made based on thyroid function tests, particularly TSH levels, to ensure the patient is euthyroid, as emphasized in 2.
- Special populations: Elderly patients or those with heart disease may require lower starting doses, with gradual increases, while certain conditions like congenital hypothyroidism may require different initial dosing strategies, as discussed in 3, 4, and 6.
- Administration: Levothyroxine should be taken on an empty stomach, 30-60 minutes before breakfast, with a full glass of water, and separated from substances that can interfere with its absorption, such as calcium, iron, and certain foods, as generally recommended.
Regular monitoring of thyroid function is crucial to ensure the dose is appropriate and to avoid adverse effects from too much or too little levothyroxine, as highlighted across the studies 3, 4, 5, 6, 2. The goal of treatment is to replace the thyroid hormone the body cannot produce in sufficient quantities, thereby regulating metabolism and other vital bodily functions.