Initial Treatment for Hypothyroidism
The initial treatment for hypothyroidism is oral levothyroxine sodium (T4), with dosing based on patient characteristics and risk factors. 1, 2
Diagnosis and Evaluation
Before initiating treatment, proper diagnosis should be confirmed:
- TSH and free T4 levels should be used for diagnosis in symptomatic patients 1
- Low TSH with low free T4 indicates central hypothyroidism (evaluate for hypophysitis) 1
- Persistently elevated TSH >10 mIU/L or symptomatic patients with any TSH elevation require treatment 1
Initial Dosing Algorithm
For Adults Without Risk Factors:
- Standard starting dose: 1.6 mcg/kg/day based on ideal body weight for patients <70 years old without frailty, cardiac disease, or multiple comorbidities 1, 3
- Full replacement can be started immediately in otherwise healthy adults 4
For High-Risk Patients:
- Lower starting dose: 25-50 mcg/day for patients who are 1, 4:
70 years old
- Frail
- Have cardiac disease (especially atrial fibrillation or coronary artery disease)
- Have multiple comorbidities
- Elderly patients require lower doses due to increased risk of cardiovascular complications 2
Special Populations:
- Pregnant women: Increase weekly dosage by 30% (take one extra dose twice weekly) with monthly monitoring 4
- Myxedema coma: Requires inpatient management with IV levothyroxine, steroids, and supportive care 1
Monitoring and Dose Adjustment
- Check TSH every 6-8 weeks while titrating dose 1, 3
- Target TSH within normal reference range 1
- Free T4 can help interpret ongoing abnormal TSH levels during therapy 1
- Once stable, monitor every 6-12 months or with symptom changes 1
- Low TSH on therapy suggests overtreatment or recovery of thyroid function 1
Common Pitfalls to Avoid
- Undertreatment: Persistent hypothyroid symptoms, increased cardiovascular risk 3
- Overtreatment: Can cause iatrogenic thyrotoxicosis with risk of atrial fibrillation, especially in elderly 2
- Medication interactions: Many drugs affect levothyroxine absorption and metabolism 2:
- Administer levothyroxine at least 4 hours apart from calcium, iron, antacids, and bile acid sequestrants
- Monitor patients on anticoagulants as levothyroxine increases response to these medications
- Adjust antidiabetic medications as needed, as levothyroxine may worsen glycemic control
Treatment Considerations
- Nearly one-third of treated patients still exhibit symptoms despite normalized TSH 5
- Availability of intermediate tablet strengths (between 25-75 mcg) may facilitate more precise dosing 6
- Combined levothyroxine plus liothyronine (T3) therapy is not recommended as first-line treatment, even in patients with persistent symptoms and normal TSH 4, 7
Clinical Outcomes
Proper treatment of hypothyroidism with levothyroxine improves: