When to use Propylthiouracil (PTU) vs methimazole for hyperthyroidism treatment?

From the Guidelines

Propylthiouracil (PTU) should be used instead of methimazole during the first trimester of pregnancy due to the lower risk of birth defects, while methimazole is preferred in the second and third trimesters due to the risk of hepatotoxicity associated with PTU. When deciding between PTU and methimazole for hyperthyroidism treatment, it's crucial to consider the patient's pregnancy status and trimester, as this significantly influences the choice of medication 1.

Key Considerations

• PTU is preferred in the first trimester because methimazole may have teratogenic effects 1.
• Methimazole is generally preferred over PTU in non-pregnant patients or in the second and third trimesters due to its better safety profile and once-daily dosing 1.
• Typical starting doses for methimazole range from 10-30 mg daily, while PTU is dosed at 100-300 mg divided three times daily.
• Both medications inhibit thyroid hormone synthesis, but PTU also blocks peripheral conversion of T4 to T3, making it useful in thyroid storm.
• Patients should be monitored for potential side effects, including hepatotoxicity with PTU and agranulocytosis with methimazole, with regular liver function and complete blood count checks 1.

Monitoring and Safety

• Regular monitoring of liver function and complete blood counts is essential, especially during the first months of therapy.
• The risk of hepatotoxicity with PTU and agranulocytosis with methimazole necessitates careful patient selection and monitoring.
• Achieving euthyroidism before pregnancy is recommended to minimize maternal and neonatal morbidity 1.

From the FDA Drug Label

INDICATIONS AND USAGE Methimazole tablets, USP are indicated: In patients with Graves’ disease with hyperthyroidism or toxic multinodular goiter for whom surgery or radioactive iodine therapy is not an appropriate treatment option. To ameliorate symptoms of hyperthyroidism in preparation for thyroidectomy or radioactive iodine therapy. CLINICAL PHARMACOLOGY Methimazole inhibits the synthesis of thyroid hormones and thus is effective in the treatment of hyperthyroidism.

The decision to use PTU vs methimazole for hyperthyroidism treatment depends on several factors, including:

• Graves’ disease: Methimazole is indicated for patients with Graves’ disease with hyperthyroidism or toxic multinodular goiter.
• Pregnancy: PTU is often preferred in the first trimester of pregnancy due to the potential risk of methimazole-induced birth defects 2.
• Liver function: Methimazole is metabolized in the liver, so PTU may be preferred in patients with liver dysfunction.
• Side effect profile: Methimazole has a higher risk of agranulocytosis and hepatotoxicity, while PTU has a higher risk of liver damage.

However, the provided drug labels do not directly compare PTU and methimazole, and the choice between the two ultimately depends on individual patient factors and clinical judgment 2.

From the Research

Choosing Between PTU and Methimazole for Hyperthyroidism Treatment

The decision to use Propylthiouracil (PTU) versus methimazole for hyperthyroidism treatment depends on several factors, including the patient's condition, potential side effects, and specific circumstances such as pregnancy.

• Pregnancy Considerations: In the case of pregnancy-related hyperthyroidism, PTU is often recommended during the first trimester due to its lower risk of birth defects compared to methimazole 3, 4. Methimazole may be associated with a higher risk of congenital anomalies such as aplasia cutis, esophageal atresia, and choanal atresia.
• Side Effects: PTU has a higher risk of liver function injury and elevated transaminase levels compared to methimazole 3. However, both drugs can cause agranulocytosis, a potentially life-threatening decrease in white blood cells, although the incidence is relatively low 5.
• Efficacy and Dosage: Methimazole can be effective in a single daily dose regimen for treating hyperthyroidism, with most patients achieving a euthyroid state within a few months 6. PTU may achieve euthyroidism more rapidly than methimazole in some cases.
• General Treatment Guidelines: Methimazole is often considered the drug of choice for hyperthyroidism treatment due to its longer half-life and lower incidence of severe side effects 7. However, PTU is a viable alternative, especially in situations where methimazole is contraindicated or not tolerated.