Thyroid & Adrenal
Treatment of choice of thyrotoxicosis in pregnancy is:
a. Antithyroid medications are generally administered in preparation for radioactive iodine ablation or surgery.
b. The medications commonly used are propylthiouracil (PTU, 100 to 300 mg three times daily) and methimazole (10 to 30 mg three times daily).
c. Methimazole has a longer half-life and can be dosed once daily. Both drugs reduce thyroid hormone production by inhibiting the organic binding of iodine and the coupling of iodotyrosines (mediated by thyroid peroxidase).
d. In addition, PTU also inhibits the peripheral conversion of T4 to T3, making it useful for the treatment of thyroid storm.
e. Both drugs can cross the placenta, inhibiting fetal thyroid function, and are excreted in breast milk, although PTU has a lower risk of transplacental transfer.
f. Methimazole is also associated with congenital aplasia, therefore PTU is more preferred in pregnant and breast-feeding women.
g. Side effects of treatment include reversible granulocytopenia, skin rashes, fever, peripheral neuritis, polyarteritis, vasculitis, and, rarely, agranulocytosis and aplastic anemia.
h. Surgery should be postponed until the granulocyte count reaches 1000 cells/m3.
i. The dose of antithyroid medication is titrated as needed in accordance with TSH and T4 levels.
j. Most patients have improved symptoms in 2 weeks and become euthyroid in about 6 weeks..
k. Treatment with antithyroid medications is associated with a high relapse rate when these drugs are discontinued, with 40 to 80% of patients developing recurrent disease after a 1- to 2-year course.
l. Patients with small glands are less likely to recur so that treatment for curative intent is reserved for patients with small, nontoxic goiters (<40 g), mildly elevated thyroid hormone levels, and rapid decrease in gland size with antithyroid medications.
m. Propranolol is the most commonly prescribed medication in doses of about 20 to 40 mg four times daily.