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PEBC: What You Need to Know: Antithyroid Agents

Examples: Methimazole (MMI) and Propylthiouracil (PTU)

Choice: Methimazole is preferred over propylthiouracil due to a slightly better safety profile and potency

Pregnancy: In first trimester, propylthiouracil is preferred, whereas second and third trimester, methimazole is preferred

Dosing: divided doses 2 to 3 doses, with food

Adverse Effects:


-joint pain, upset stomach

-increased liver function tests and hepatotoxicity (higher risk with PTU)

-agranulocytosis (rare): monitor for signs of infection (sore throat, fever)

-nephrotoxicity (rare)


-warfarin: may lead to a decrease in INR

-theophylline: may lead to increased theophylline levels

-digoxin: may increase digoxin levels

-avoid other medications that cause agranulocytosis: clozapine

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