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. Some patients require a lower starting dose.
The starting dose of levothyroxine is 1.6 mcg/kg/day for adults with primary, secondary, or tertiary hypothyroidism. However, some patients may require a lower starting dose, especially those at risk of atrial fibrillation or with underlying cardiac disease 1.
- The dosage may be titrated by 12.5 to 25 mcg increments every 4 to 6 weeks, as needed until the patient is euthyroid.
- For patients with underlying cardiac disease, the dosage should be titrated every 6 to 8 weeks.
- For geriatric patients, a lower starting dose (less than 1.6 mcg/kg/day) is recommended.
- For pediatric patients, the starting daily dosage is based on body weight and changes with age, as described in Table 2.
- The dosage should be adjusted based on clinical response and laboratory parameters.
From the Research
The starting dose of levothyroxine should be individualized, but typically ranges from 25 to 50 micrograms (mcg) daily for most adults with hypothyroidism, as seen in the most recent study 2. For elderly patients or those with heart disease, a lower starting dose of 12.5-25 mcg daily is recommended to avoid cardiac stress, as indicated by the study 3. Young, otherwise healthy patients might start at 50-100 mcg daily. Dosing is individualized based on several factors including age, weight, severity of hypothyroidism, and presence of other medical conditions. Some key points to consider when initiating levothyroxine therapy include:
- Starting with a lower dose and gradually increasing as needed to minimize the risk of cardiac arrhythmias, as discussed in the study 4
- Monitoring thyroid function tests (TSH and sometimes free T4) in 6-8 weeks to assess response, with dose adjustments made in 12.5-25 mcg increments until the patient reaches a euthyroid state, as recommended by the study 5
- Being consistent with timing of medication and avoiding taking it with calcium, iron supplements, or certain foods that can interfere with absorption, as suggested by the study 6
- Considering the potential impact of levothyroxine on cardiac function, particularly in older adults with mild subclinical hypothyroidism, as seen in the study 2. Levothyroxine works by replacing the thyroid hormone that the body cannot produce in sufficient quantities, helping restore normal metabolism. The most recent and highest quality study 2 provides the best guidance on the starting dose of levothyroxine, and its findings should be prioritized when making treatment decisions.