From the Guidelines
For overt hypothyroidism, treatment should begin with levothyroxine (T4) at a dose of 1.6 mcg/kg/day for most adults, typically starting at 50-100 mcg daily, while for subclinical hypothyroidism, treatment is recommended when TSH exceeds 10 mIU/L or if TSH is between 4.5-10 mIU/L with symptoms or positive thyroid antibodies, starting at a lower dose of 25-50 mcg daily. The primary goal in treating both conditions is to achieve a TSH level within the normal range (0.4-4.0 mIU/L) to minimize morbidity, mortality, and improve quality of life 1.
Key Considerations for Overt Hypothyroidism
- Elderly patients or those with cardiovascular disease should start at a lower dose of 25-50 mcg daily to avoid adverse cardiac effects.
- Dose adjustments should be made every 6-8 weeks based on TSH levels.
- Liothyronine (T3) is not routinely recommended as first-line therapy but may be considered in patients who remain symptomatic despite normalized TSH on levothyroxine alone, typically added at 5-10 mcg daily, often split into two doses 1.
Key Considerations for Subclinical Hypothyroidism
- Treatment is not universally recommended for TSH levels between 4.5 and 10 mIU/L without symptoms or positive thyroid antibodies, as the benefits of early therapy are not clearly established 1.
- For patients with TSH levels between 4.5 and 10 mIU/L and symptoms suggestive of hypothyroidism, a trial of levothyroxine may be considered, with continuation of therapy based on clear symptomatic benefit.
- Regular monitoring of TSH levels is essential, with checks 6-8 weeks after any dose change and annually once stable, to ensure that the treatment is effective and to minimize the risk of overtreatment or undertreatment.
General Recommendations
- Medication should be taken on an empty stomach, 30-60 minutes before breakfast, and separated from medications or supplements containing calcium, iron, or aluminum by at least 4 hours to ensure optimal absorption.
- The physiological basis for preferring T4 is that it serves as a prohormone that converts to T3 in peripheral tissues, providing more stable hormone levels than direct T3 supplementation 1.
From the FDA Drug Label
INDICATIONS AND USAGE Levothyroxine sodium tablets are a L-thyroxine (T4) indicated in adult and pediatric patients, including neonates, for: • Hypothyroidism: As replacement therapy in primary (thyroidal), secondary (pituitary), and tertiary (hypothalamic) congenital or acquired hypothyroidism.
DOSAGE AND ADMINISTRATION • Administer once daily, preferably on an empty stomach, one-half to one hour before breakfast with a full glass of water.
The dosage of thyroid hormones is determined by the indication and must in every case be individualized according to patient response and laboratory findings.
Treatment Guidelines:
- Overt Hypothyroidism: Levothyroxine (T4) is indicated for replacement therapy in primary, secondary, and tertiary congenital or acquired hypothyroidism.
- Subclinical Hypothyroidism: There is no direct information in the provided drug labels regarding the treatment of subclinical hypothyroidism.
- Levothyroxine (T4) Dosage: The starting dose depends on various factors, including age, body weight, cardiovascular status, and concomitant medications. The dosage should be individualized according to patient response and laboratory findings.
- Liothyronine (T3) Indications: Liothyronine (T3) may be used in preference to levothyroxine (T4) during radioisotope scanning procedures, when impairment of peripheral conversion of T4 to T3 is suspected, or in cases of myxedema coma.
- Key Considerations:
- Titrate the dose of levothyroxine sodium carefully and monitor response to titration.
- Initiate levothyroxine sodium at less than the full replacement dose in the elderly and in patients with underlying cardiovascular disease.
- Give the lowest effective dose to avoid over-replacement and decreased bone mineral density. 2, 3, 2
From the Research
Overt Hypothyroidism vs Subclinical Hypothyroidism
- Overt hypothyroidism is characterized by high TSH levels and low free T4 levels, and is often symptomatic 4, 5.
- Subclinical hypothyroidism is characterized by high TSH levels and normal free T4 levels, and is usually asymptomatic 4, 6, 7.
Treatment Guidelines
- Levothyroxine therapy is recommended for patients with overt hypothyroidism and a blood TSH concentration above 10 mIU/L 4, 5.
- For subclinical hypothyroidism, treatment is not necessary unless the TSH exceeds 7.0-10 mIU/L 6, 7.
- The dosage of levothyroxine should be started at 1.5 to 1.8 mcg per kg per day for young adults, and 12.5 to 50 mcg per day for elderly patients or those with coronary artery disease 4, 5, 8.
Indications for Liothyronine (T3)
- Combined treatment with levothyroxine and liothyronine may be preferred for some hypothyroid patients who are dissatisfied with treatment, especially those with a polymorphism in type 2 deiodinase 6.
- However, there is no evidence that adding triiodothyronine is beneficial for patients with persistent symptoms and normal levels of thyroid-stimulating hormone 5.
Special Considerations
- TSH goals are age-dependent, with a 97.5 percentile (upper limit of normal) of 3.6 mIU/L for patients under age 40, and 7.5 mIU/L for patients over age 80 6.
- Women with hypothyroidism who become pregnant should increase their weekly dosage of levothyroxine by 30% up to nine doses per week 5.
- Patients with subclinical hypothyroidism and serum thyrotropin levels of 10 mU/L or higher, or young and middle-aged individuals with subclinical hypothyroidism and symptoms consistent with mild hypothyroidism, may benefit from treatment 7.