The first-line pharmacologic treatment for primary hypothyroidism is which medication?

The first-line pharmacologic treatment for primary hypothyroidism is which medication?

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

Answer: (B)

Levodothyroxine is the go-to treatment because replacing with a stable, long-acting thyroid hormone that the body can convert as needed provides reliable normalization of thyroid function. Levothyroxine is synthetic T4, and the body converts T4 to the active T3 in tissues, giving steady effects with predictable dosing. Its long half-life allows once-daily dosing, consistent absorption, wide availability, and a strong track record of safety and efficacy in correcting the low thyroid hormone state seen in primary hypothyroidism. Start around 1.6 mcg/kg/day in a healthy adult, but lower initial doses are used for older patients or those with heart disease, with gradual titration every 4–6 weeks guided by TSH (aiming to bring TSH within the reference range). Monitor long-term with periodic TSH and free T4 to ensure stability. The other medications listed are antithyroid drugs or, in the case of a T3-only preparation, have more fluctuating effects and are not preferred as first-line replacement therapy.

Levodothyroxine is the go-to treatment because replacing with a stable, long-acting thyroid hormone that the body can convert as needed provides reliable normalization of thyroid function. Levothyroxine is synthetic T4, and the body converts T4 to the active T3 in tissues, giving steady effects with predictable dosing. Its long half-life allows once-daily dosing, consistent absorption, wide availability, and a strong track record of safety and efficacy in correcting the low thyroid hormone state seen in primary hypothyroidism. Start around 1.6 mcg/kg/day in a healthy adult, but lower initial doses are used for older patients or those with heart disease, with gradual titration every 4–6 weeks guided by TSH (aiming to bring TSH within the reference range). Monitor long-term with periodic TSH and free T4 to ensure stability. The other medications listed are antithyroid drugs or, in the case of a T3-only preparation, have more fluctuating effects and are not preferred as first-line replacement therapy.