In severe hypothyroidism with bradycardia and fatigue, which medication is standard therapy to replace deficient thyroid hormone?

• A. Methimazole
• B. Propylthiouracil
• C. Levothyroxine
• D. Liothyronine

Answer: (C)

When hypothyroidism is present, the goal is to replace the missing thyroid hormone. Levothyroxine, a synthetic form of T4, is the standard choice because it provides a stable, long-acting dose that the body can convert to the active T3 in tissues as needed. This conversion gives steady TSH levels and gradual symptom improvement, which is especially important in a patient with fatigue and bradycardia.

The other options aren’t used for replacement in hypothyroidism. Methimazole and propylthiouracil inhibit thyroid hormone synthesis and are used to treat hyperthyroidism, not to replace hormones. Liothyronine supplies only T3 and can cause more fluctuation in hormone levels and potential cardiac side effects, so it’s not preferred as routine replacement. In most adults, starting with levothyroxine and titrating based on TSH and clinical response provides the safest, most effective recovery of energy and heart rate. In severe cases or when oral dosing isn’t possible, intravenous levothyroxine is used.