What is the initial therapy for a pregnant woman with symptoms of hyperthyroidism, including tachycardia, diaphoresis, and a diffuse thyroid gland enlargement, with a serum Thyroid-Stimulating Hormone (TSH) level of less than 0.01, and taking no medications, presenting with fatigue and sweating?

From the Guidelines

Propylthiouracil (PTU) is the recommended initial therapy for this pregnant woman with hyperthyroidism. The patient's symptoms of fatigue, sweating, tachycardia, thyroid enlargement, and undetectable TSH level indicate hyperthyroidism, likely Graves' disease. Since she is pregnant, medication selection requires special consideration. PTU is preferred over methimazole during the first trimester of pregnancy because methimazole is associated with a rare embryopathy, as noted in the guidelines for managing thyroid disease in pregnancy 1. PTU blocks new thyroid hormone synthesis and inhibits peripheral conversion of T4 to T3. The typical starting dose is 100-150 mg three times daily, with dose adjustments based on thyroid function tests every 2-4 weeks, as recommended in the management of hyperthyroidism in pregnancy 1. The goal is to maintain free T4 in the upper normal range using the lowest possible dose to minimize fetal exposure.

Some key points to consider in the management of hyperthyroidism in pregnancy include:

• The importance of achieving euthyroidism before pregnancy to minimize maternal and neonatal morbidity 1
• The use of beta-blockers like propranolol for temporary symptom control, but not as a definitive treatment for hyperthyroidism 1
• The potential side effects of thioamides, such as agranulocytosis, hepatitis, vasculitis, and thrombocytopenia, which require monitoring 1
• The consideration of switching to methimazole after the first trimester due to its less frequent dosing and lower risk of hepatotoxicity 1

Overall, the management of hyperthyroidism in pregnancy requires careful consideration of the potential risks and benefits of different treatment options, with the goal of achieving euthyroidism and minimizing maternal and neonatal morbidity.

From the FDA Drug Label

In pregnant women with untreated or inadequately treated Graves’ disease, there is an increased risk of adverse events of maternal heart failure, spontaneous abortion, preterm birth, stillbirth and fetal or neonatal hyperthyroidism Because methimazole crosses placental membranes and can induce goiter and cretinism in the developing fetus, hyperthyroidism should be closely monitored in pregnant women and treatment adjusted such that a sufficient, but not excessive, dose be given during pregnancy Due to the rare occurrence of congenital malformations associated with methimazole use, it may be appropriate to use an alternative anti-thyroid medication in pregnant women requiring treatment for hyperthyroidism particularly in the first trimester of pregnancy during organogenesis.

The initial therapy for a pregnant woman with symptoms of hyperthyroidism is not explicitly stated in the provided drug labels. However, it can be inferred that methimazole may be used to treat hyperthyroidism in pregnant women, but with caution and close monitoring due to the potential risks to the fetus.

• The treatment should be adjusted to give a sufficient, but not excessive, dose during pregnancy.
• It may be appropriate to use an alternative anti-thyroid medication in pregnant women requiring treatment for hyperthyroidism, particularly in the first trimester of pregnancy during organogenesis 2 2.

From the Research

Initial Therapy for Hyperthyroidism in Pregnancy

The initial therapy for a pregnant woman with symptoms of hyperthyroidism, including tachycardia, diaphoresis, and a diffuse thyroid gland enlargement, with a serum Thyroid-Stimulating Hormone (TSH) level of less than 0.01, and taking no medications, presenting with fatigue and sweating, is typically antithyroid drugs.

• The antithyroid drugs mainly include thioimidazole (carbimazole, methimazole=thiamazole) and propylthiouracil 3.
• Propylthiouracil (PTU) is often preferred during the first trimester of pregnancy due to its lower teratogenic risk compared to methimazole (MMI) 4, 5, 6.
• However, PTU has been associated with a rare but serious form of hepatic failure, and its use should be limited to the first trimester of pregnancy 4, 5.
• Methimazole (MMI) causes a specific pattern of rare teratogenic effects after first trimester exposure, and it is often used after the first trimester 4, 5.

Treatment Considerations

• The choice between PTU and MMI should be based on individual patient factors and the specific circumstances of the pregnancy 4, 6.
• It is essential to monitor thyroid function regularly while the patient is on antithyroid drugs to avoid dose-dependent hypothyroidism 3.
• Patients should be advised to seek medical help immediately if they experience symptoms such as fever, sore throat, malaise, abdominal complaints, or jaundice, which could indicate serious side effects of antithyroid drugs 3.