Initial Treatment for Hypothyroidism
The initial treatment for hypothyroidism is oral levothyroxine (T4) monotherapy, which remains the standard of care for managing primary hypothyroidism. 1, 2
Dosing Recommendations
- For patients under 70 years without cardiovascular disease, start levothyroxine at 1.6 mcg/kg/day based on ideal body weight 3
- For patients over 70 years OR with cardiovascular disease OR multiple comorbidities, start with a lower dose of 25-50 mcg/day and gradually titrate upward to avoid exacerbating cardiac conditions 3, 4
- For patients with overt hypothyroidism, the typical starting dose for adults is 1.5 to 1.8 mcg per kg per day 5
- When treating subclinical hypothyroidism with TSH >10 mIU/L, full replacement doses are generally recommended 2
Special Populations Requiring Treatment
- All patients with overt hypothyroidism (elevated TSH with low free T4) should receive treatment 2
- Patients with subclinical hypothyroidism with TSH >10 mIU/L should be treated 2, 5
- Pregnant women or women planning pregnancy with elevated TSH should be treated with levothyroxine to restore TSH to the reference range 6, 4
- For patients with both adrenal insufficiency AND hypothyroidism, ALWAYS start corticosteroid replacement BEFORE thyroid hormone to prevent precipitating adrenal crisis 3, 7
Monitoring and Dose Adjustment
- Check TSH and free T4 levels 6-8 weeks after starting treatment or changing dose 3, 5
- Target TSH within reference range (0.4-4.0 mIU/L) for primary hypothyroidism 8
- For central hypothyroidism, target free T4 in upper half of reference range 3
- Once stable, annual monitoring of TSH is recommended to avoid overtreatment or undertreatment 1
Common Pitfalls to Avoid
- Starting with full doses in elderly patients or those with cardiovascular disease can lead to cardiac complications; use lower starting doses (25-50 mcg/day) in these populations 3, 4
- Initiating thyroid replacement before corticosteroids in patients with adrenal insufficiency can precipitate adrenal crisis 3, 7
- Over-replacement is common in clinical practice and is associated with increased risk of atrial fibrillation and osteoporosis 2
- Failing to adjust dosage during pregnancy can lead to inadequate treatment; pregnancy may increase levothyroxine requirements 4
Treatment Controversies
- For subclinical hypothyroidism with TSH between 4.5 and 10 mIU/L, routine treatment is not recommended by some guidelines, but thyroid function tests should be repeated at 6-12 month intervals 6
- Combined levothyroxine plus liothyronine (T3) therapy has been evaluated in multiple clinical trials, but until clear advantages are demonstrated, levothyroxine alone should remain the treatment of choice 9
- Treatment of subclinical hypothyroidism in patients with serum TSH up to 10 mIU/L should probably be avoided in those aged >85 years 2