There are no official guidelines to assist in answering this question. I will search for relevant research papers instead.
From the FDA Drug Label
The average full replacement dose of levothyroxine sodium is approximately 1.7 mcg/kg/day (e.g., 100-125 mcg/day for a 70 kg adult). For most patients older than 50 years or for patients under 50 years of age with underlying cardiac disease, an initial starting dose of 25-50 mcg/day of levothyroxine sodium is recommended, with gradual increments in dose at 6-8 week intervals, as needed. The recommended starting dose of levothyroxine sodium in elderly patients with cardiac disease is 12.5-25 mcg/day, with gradual dose increments at 4-6 week intervals. In patients with severe hypothyroidism, the recommended initial levothyroxine sodium dose is 12.5-25 mcg/day with increases of 25 mcg/day every 2-4 weeks, accompanied by clinical and laboratory assessment, until the TSH level is normalized.
The starting dose for levothyroxine (T4) replacement therapy is:
- 25-50 mcg/day for most patients older than 50 years or for patients under 50 years of age with underlying cardiac disease
- 12.5-25 mcg/day for elderly patients with cardiac disease
- 12.5-25 mcg/day for patients with severe hypothyroidism
- 10-15 mcg/kg/day for newborn infants
- 25 mcg/day for infants at risk for cardiac failure 1
From the Research
Starting Dose for Levothyroxine (T4) Replacement Therapy
The starting dose for levothyroxine (T4) replacement therapy varies based on the patient's age, weight, and medical condition.
- For young adults, the starting dose is usually around 1.5 microg/kg per day, taken on an empty stomach 2, 3.
- For elderly patients and those with coronary artery disease, the starting dose should be lower, typically ranging from 12.5 to 50 microg per day 2, 3.
- Patients with significant comorbidities, low body weight, or residual thyroid function may also require a lower starting dose, such as 25-50 µg per day 4.
Factors Influencing the Starting Dose
Several factors can influence the starting dose of levothyroxine, including:
- Body weight: The dose is often calculated based on the patient's body weight, with a typical dose range of 1.5-1.8 mcg/kg per day 3.
- Age: Elderly patients may require lower doses due to decreased thyroid hormone production and increased sensitivity to thyroxine 2, 3.
- Medical condition: Patients with certain medical conditions, such as coronary artery disease or thyroid cancer, may require adjusted doses 2, 5.
- Thyroid function: Patients with residual thyroid function or those who have undergone total thyroidectomy may require different starting doses 6, 5.