説明
Long-term metformin use has been associated with modest reductions in TSH levels independent of levothyroxine dose, potentially complicating thyroid function monitoring in diabetic patients.
機序
Metformin may lower TSH via AMPK-mediated effects on hypothalamic-pituitary axis signalling; this pharmacodynamic effect can mimic adequately treated hypothyroidism on biochemical testing.
臨床的意義
Population-level studies show lower TSH values in metformin-treated patients on levothyroxine; the clinical significance for thyroid function is low, but it can lead to unnecessary levothyroxine dose reductions.
対処法
Be aware of metformin's TSH-lowering effect when interpreting thyroid function tests; do not reduce levothyroxine dose solely based on low-normal TSH in patients on metformin without clinical symptoms of hyperthyroidism.