When to initiate levothyroxine (T4) therapy for hypothyroidism?

From the Guidelines

Treatment for hypothyroidism should begin when the TSH level is greater than 10.0 mIU/L, as this is the threshold for initiation of treatment based on expert opinion 1. When starting medication for hypothyroidism, the standard medication is levothyroxine, usually started at 1.6 mcg/kg body weight per day for otherwise healthy adults, though lower doses (25-50 mcg daily) are recommended for elderly patients or those with heart disease, as suggested by recent guidelines 1. Some key considerations when initiating treatment include:

• Starting with a lower dose in patients older than 70 years and/or frail patients with multiple comorbidities, including cardiac disease 1
• Monitoring asymptomatic patients with FT4 that remains in the reference range before treating to determine whether there is recovery to normal within 3-4 weeks 1
• Adjusting dosage based on TSH levels checked 6-8 weeks after starting treatment, with the goal of bringing TSH into the normal range (typically 0.4-4.0 mIU/L)
• Being aware that development of a low TSH on therapy suggests overtreatment or recovery of thyroid function and dose should be reduced or discontinued with close follow-up 1. Proper treatment is important because untreated hypothyroidism can lead to fatigue, weight gain, cold intolerance, and more serious complications like heart problems and infertility.

From the FDA Drug Label

Since TSH levels may increase during pregnancy, TSH should be monitored and levothyroxine sodium dosage adjusted during pregnancy Hypothyroidism diagnosed during pregnancy should be promptly treated Rapid restoration of normal serum T4 concentrations is essential for preventing the adverse effects of congenital hypothyroidism on cognitive development as well as on overall physical growth and maturation. Therefore, initiate levothyroxine sodium therapy immediately upon diagnosis.

Initiation of Medicine for Hypothyroidism:

• Hypothyroidism diagnosed during pregnancy should be promptly treated.
• For congenital hypothyroidism, initiate levothyroxine sodium therapy immediately upon diagnosis.
• In the geriatric population, initiate levothyroxine sodium at less than the full replacement dose 2.

From the Research

Starting Medicine for Hypothyroidism

When to start medicine for hypothyroidism depends on various factors, including the severity of the condition and the presence of symptoms.

• The treatment of hypothyroidism with levothyroxine is effective and simple, but recommendations for the starting dose vary considerably 3.
• A prospective, randomized, double-blind trial compared a full starting levothyroxine dose of 1.6 mug/kg with a low starting dose of 25 mug (increased every 4 weeks) in patients with newly diagnosed cardiac asymptomatic hypothyroidism, and found that a full starting dose of levothyroxine in cardiac asymptomatic patients with primary hypothyroidism is safe and may be more convenient and cost-effective than a low starting dose regimen 3.
• For patients who remain symptomatic on LT4 therapy, clinical guidelines recommend, on a trial basis, therapy with LT4+LT3, with a starting point of reducing the LT4 dose by 25 mcg/day and adding 2.5-7.5 mcg liothyronine (LT3) once or twice a day 4.

Factors to Consider

Several factors should be considered when deciding when to start medicine for hypothyroidism, including:

• The severity of hypothyroidism and age of the patient 3.
• The presence of cardiac symptoms or events 3.
• The patient's response to treatment, including the improvement of signs and symptoms and quality of life 3.
• The potential benefits and risks of combination therapy with LT4+LT3 4, 5, 6.

Treatment Guidelines

Treatment guidelines for hypothyroidism recommend:

• Starting with levothyroxine (LT4) as the initial treatment 4, 5, 6.
• Optimizing LT4 doses to achieve a TSH level in the 0.3-2.0 mU/L range for 3 to 6 months before assessing the therapeutic response 6.
• Considering a trial of liothyronine/levothyroxine combined therapy for patients with confirmed overt hypothyroidism and persistent symptoms who have had adequate treatment with levothyroxine and in whom other comorbidities have been excluded 6.