From the Guidelines
Thyroxine dosing should be titrated based on TSH levels with a goal of maintaining TSH within the normal reference range, starting with an initial dose of approximately 1.6 mcg/kg/d for patients without risk factors, and 25-50 mcg for those older than 70 years or with multiple comorbidities, including cardiac disease. When titrating thyroxine dosing, it is essential to consider the patient's age, weight, and comorbidities. For patients without risk factors, such as those under 70 years old, not frail, and without cardiac disease or multiple comorbidities, the initial dose can be estimated using ideal body weight for a dose of approximately 1.6 mcg/kg/d, as suggested by 1. For those older than age 70 years and/or frail patients with multiple comorbidities, including cardiac disease, it is recommended to start with a lower dose of 25-50 mcg and titrate up gradually, as indicated by 1. Key considerations when titrating thyroxine dosing include:
- Monitoring TSH levels 6-8 weeks after initiation or any dose change
- Adjusting the dose by 12.5-25 mcg increments based on TSH levels
- Maintaining TSH within the normal reference range to avoid symptoms of over-replacement or under-replacement
- Regular monitoring of TSH levels every 6-12 months once the patient is stable on an appropriate dose, as well as after any changes in dose or clinical status. It is also crucial to consider the potential for elevated TSH in the recovery phase of thyroiditis, and to monitor asymptomatic patients with FT4 within the reference range before treating, as noted by 1. Additionally, the development of a low TSH on therapy suggests overtreatment or recovery of thyroid function, and the dose should be reduced or discontinued with close follow-up, as recommended by 1.
From the FDA Drug Label
Titrate the dosage (every 2 weeks) as needed based on serum TSH or free-T4 until the patient is euthyroid In adult patients with primary hypothyroidism, monitor serum TSH levels after an interval of 6 to 8 weeks after any change in dosage. The general aim of therapy is to normalize the serum TSH level Failure of the serum T4 to increase into the upper half of the normal range within 2 weeks of initiation of levothyroxine sodium therapy and/or of the serum TSH to decrease below 20 IU per litre within 4 weeks may indicate the patient is not receiving adequate therapy
To titrate thyroxine dosing based on TSH, monitor serum TSH levels after an interval of 6 to 8 weeks after any change in dosage. The goal is to normalize the serum TSH level. If the serum TSH does not decrease below 20 IU per litre within 4 weeks, it may indicate that the patient is not receiving adequate therapy. Adjust the dosage every 2 weeks as needed based on serum TSH or free-T4 until the patient is euthyroid 2.
- Key points:
- Monitor serum TSH levels every 6 to 8 weeks after any change in dosage
- Normalize the serum TSH level
- Adjust the dosage every 2 weeks as needed based on serum TSH or free-T4
- Assess compliance, dose of medication administered, and method of administration prior to increasing the dose of levothyroxine sodium
From the Research
Thyroxine Dosing Based on TSH
To titrate thyroxine dosing based on TSH, the following steps can be considered:
- Synthetic LT4 is titrated to bring the level of TSH within a predefined "normal" reference range, which is now established as the mainstay of treatment for hypothyroidism 3
- The treatment goal is to restore thyroid hormone function, and LT4 monotherapy is adequate for most people with hypothyroidism 4, 3
- However, a small subset of patients may not feel well on monotherapy, and a trial of combination therapy with T4 and T3 may be appropriate 5
Patient Selection and Monitoring
When considering combination therapy, it is essential to:
- Select the correct patient for a trial to avoid delaying diagnosis or worsening an undiagnosed condition 5
- Determine an appropriate starting dose, although accuracy may be limited by available formulations and cost 5
- Monitor thyroid function, benefits, and adverse effects closely, given the lack of evidence on safe long-term use 5
- Ensure patients understand the trial setup, potential risks, and provide consent 5
Clinical Considerations
- The level of TSH influences the rate of secretion of thyroid hormones, and treatment should aim to bring TSH within a normal reference range 3
- Combination therapy may be preferred by some patients, with a higher proportion of patients choosing combined therapy over monotherapy 4
- Adverse events and reactions appear to be similar across both monotherapy and combination therapy groups, although more research is needed to confirm this observation 4