What is the starting dose of levothyroxine (T4) for a 150-pound female patient with a Thyroid-Stimulating Hormone (TSH) level of 35, indicating hypothyroidism?

Levothyroxine Dosing for Hypothyroidism with TSH of 35

For a 150-pound female patient with a TSH of 35, the appropriate starting dose of levothyroxine is 1.6 mcg/kg/day, which calculates to approximately 109 mcg/day. 1

Initial Dosing Considerations

The American Thyroid Association and American College of Clinical Endocrinologists recommend the following approach for patients with overt hypothyroidism:

• For adults under 70 years without cardiac disease: 1.6 mcg/kg/day 1
• For elderly patients or those with cardiac conditions: 25-50 mcg/day 1

Since the patient has a significantly elevated TSH of 35, this indicates overt hypothyroidism requiring full replacement therapy. For a 150-pound (68 kg) female without cardiac disease or advanced age, the calculation is:

• 1.6 mcg/kg/day × 68 kg = 109 mcg/day

In clinical practice, this would typically be rounded to 100 or 112 mcg daily, depending on available tablet strengths.

Monitoring and Dose Adjustment

• Check TSH and free T4 levels 6-8 weeks after initiating therapy 1, 2
• Adjust dose by 12.5-25 mcg if TSH remains outside the target range 1
• Target TSH range for patients under 70 without cardiac disease: 0.5-2.0 mIU/L 1
• Once stable, monitor every 6-12 months 1

Important Considerations

Administration Guidelines

• Take levothyroxine on an empty stomach, 30-60 minutes before breakfast 1
• Avoid taking within 4 hours of calcium supplements, iron, or antacids 1
• Maintain consistent brand of levothyroxine to avoid fluctuations in bioavailability 1

Cautions

• Avoid overtreatment: Overtreatment can lead to iatrogenic thyrotoxicosis with risks of osteoporosis, fractures, or cardiac issues 1, 2
• Special populations: If the patient is elderly or has cardiac disease, start with a lower dose (25-50 mcg/day) 1, 2
• Pregnancy considerations: If the patient becomes pregnant, increase weekly dosage by 30% (take one extra dose twice weekly) 2, 3

Common Pitfalls

1. Inadequate follow-up: Failure to check TSH levels 6-8 weeks after initiation or dose change 1
2. Medication interactions: Not accounting for drugs that affect levothyroxine absorption 1
3. Overtreatment: About 25% of patients on levothyroxine are inadvertently maintained on doses high enough to make TSH undetectable 1
4. Undertreatment: Inadequate dosing can lead to persistent hypothyroid symptoms 3

By following these guidelines, most patients achieve symptom relief and normalized thyroid function with appropriate levothyroxine replacement therapy.