What is the amount of placenta passage of MMI and PTU?
All antithyroid drugs cross the placenta and may potentially affect fetal thyroid function (22).
Although PTU is more extensively bound to serum albumin than MMI and hypothetically less of it might be transferred through placenta than MMI, it has been shown that placental passage of PTU and MMI is similar. A study showed that transfer rates across the placenta were independent of the perfusate protein concentration, and this might be due to highly efficient placental extraction of the unbound drug (23). Cord PTU levels were higher than maternal concentrations in hyperthyroid pregnant patients treated with PTU until term (24). In addition, there were no differences in thyroid hormone and TSH concentrations in cord blood at birth between the MMI- and the PTU-treated newborn