levothyroxine + methimazole

Levothyroxine + methimazole is a combination therapy used primarily in the management of hyperthyroidism, particularly Graves' disease. This regimen, often referred to as "block-and-replace," involves administering methimazole at a dose sufficient to completely suppress endogenous thyroid hormone production, while simultaneously providing levothyroxine to maintain normal thyroid hormone levels. Methimazole acts by inhibiting thyroid peroxidase, thereby blocking the synthesis of thyroid hormones (T3 and T4). Levothyroxine is a synthetic form of thyroxine (T4) that replaces or supplements endogenous hormone. The combination aims to stabilize thyroid function more effectively than methimazole alone in certain patients—especially those with fluctuating or poorly controlled disease—and may reduce recurrence rates and adverse effects associated with overtreatment or undertreatment. However, evidence suggests it does not improve long-term remission rates compared to titration therapy with antithyroid drugs alone[1][2][3][4][6].

Other names

block-and-replace therapymethimazole + thyroxine