Initial Treatment for Hypothyroidism
The initial treatment for hypothyroidism is oral levothyroxine sodium (T4) monotherapy, with dosing tailored to patient-specific factors including age and comorbidities. 1, 2, 3
Diagnosis Confirmation
- Diagnosis of hypothyroidism is confirmed with elevated TSH and low free T4 levels, indicating primary hypothyroidism 2, 3
- Distinguish between primary hypothyroidism (elevated TSH, low free T4) and central hypothyroidism (low/normal TSH, low free T4) as management approaches differ 2
- Multiple tests should be done over a 3-6 month interval to confirm abnormal findings before initiating treatment 1
Initial Dosing Algorithm
Standard Dosing
- For patients <70 years without cardiovascular disease: start levothyroxine at 1.6 mcg/kg/day based on ideal body weight 2, 4
- Full calculated dose can be started for most young patients without significant comorbidities 5
Modified Dosing for Special Populations
- For patients >70 years OR with cardiovascular disease OR multiple comorbidities: start with lower dose of 25-50 mcg/day and gradually titrate upward 2, 6
- For elderly patients, patients with coronary artery disease, and those with long-standing severe hypothyroidism: initiate at a lower dose to avoid cardiac complications 5, 7
- For patients with adrenal insufficiency AND hypothyroidism: ALWAYS start corticosteroid replacement BEFORE thyroid hormone to prevent precipitating adrenal crisis 2
Monitoring and Dose Adjustment
- Check TSH and free T4 levels 6-8 weeks after starting treatment or changing dose 2, 3
- Target TSH within reference range (0.4-4.0 mIU/L) for primary hypothyroidism 4
- For central hypothyroidism, target free T4 in upper half of reference range 2
- Once stabilized, monitor TSH annually to avoid overtreatment or undertreatment 3
Special Considerations
Pregnancy
- Pregnant women or women planning pregnancy who have elevated TSH should receive levothyroxine to restore TSH to reference range 1
- TSH levels may increase during pregnancy, requiring dose adjustments 7
- Maternal hypothyroidism during pregnancy is associated with higher rates of complications including spontaneous abortion, gestational hypertension, pre-eclampsia, stillbirth, and premature delivery 7
Subclinical Hypothyroidism
- All patients with subclinical hypothyroidism and TSH >10 mIU/L should be treated with levothyroxine 5
- For subclinical hypothyroidism with TSH between 4.5-10 mIU/L, treatment is not routinely recommended unless the patient is symptomatic, has infertility, goiter, or positive anti-thyroid peroxidase antibodies 1, 5
- Treatment should be considered in pregnant women with any degree of subclinical hypothyroidism 1, 5
Common Pitfalls to Avoid
- Starting thyroid replacement before corticosteroids in patients with adrenal insufficiency can precipitate adrenal crisis 2
- Over-replacement is common in clinical practice and increases risk of atrial fibrillation and osteoporosis 5
- Inadequate dose adjustment in elderly or cardiac patients can lead to adverse cardiovascular outcomes 2, 5
- Failing to educate patients about lifelong treatment requirements can lead to non-adherence 2
- Not considering drug interactions or malabsorption in patients with persistently elevated TSH despite adequate replacement dose 5
Alternative Treatment Options
- While combination therapy with levothyroxine plus liothyronine (T3) has been evaluated in multiple clinical trials, levothyroxine monotherapy remains the standard of care until clear advantages of combination therapy are demonstrated 8
- Some patients may prefer combination therapy, but this should be balanced against potential adverse events from adding liothyronine 8