Propylthiouracil
PTU
What it isThionamide inhibiting thyroid peroxidase and peripheral thyroid-hormone activation; hyperthyroidism.
Why this oneIts peripheral conversion block makes it useful in thyroid storm, and it is preferred early in pregnancy.
What limits itSevere liver failure keeps it second-line otherwise; agranulocytosis demands urgent evaluation of fever or sore throat.
FDA-approved for
- hyperthyroidism (~1947)
FDA label
Read the full label on DailyMed ↗
| FDA dosing | Population | Start | Target | Max |
|---|---|---|---|---|
| Hyperthyroidism | Adults | 300 mg/day divided q8h (TID) | maintenance 100–150 mg/day | 400 mg/day usual; occasionally 600–900 mg/day initially (severe) |
| Hyperthyroidism | Pediatric ≥6y (rare; only when alternatives inappropriate) | 50 mg/day, titrate upward |
Renal Undefined
Hepatic Undefined
Instructions
- Give total daily dose in 3 equal doses at ~8-hour intervals
- Reserve for patients intolerant of methimazole or when RAI/surgery inappropriate
Cautions
- Severe hepatotoxicity / acute liver failure — monitor, warn patient
- Myelosuppression (agranulocytosis, granulopenia, aplastic anemia, thrombocytopenia) — report fever/infection
- ANCA-positive vasculitis with severe complications/death
- Lupus-like syndrome
- Serious hypersensitivity reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis)
- Hypoprothrombinemia and bleeding
Adverse reactions
- Liver injury (hepatitis, liver failure)
- Agranulocytosis/granulopenia/aplastic anemia
- Thrombocytopenia
- Drug fever
- Lupus-like syndrome
- ANCA-associated vasculitis
- Skin rash/urticaria
- Nausea/vomiting/epigastric distress
- Arthralgia
- Paresthesias
- Loss/perversion of taste
Pregnancy May be the preferred antithyroid agent during or just before the first trimester (methimazole teratogenicity); crosses placenta and can cause fetal goiter/cretinism — use lowest effective dose; given maternal hepatotoxicity risk, consider switching to methimazole for 2nd/3rd trimesters.
Lactation Undefined
⚠ BOXED WARNING
- Severe liver injury and acute liver failure
Cost, est. cash$10–$300/month
Generic entry2023
Classes and tags
Clinical profile
Legacy pregnancy categoryUnknown / historical label unavailable
Defining liabilityPotentially fatal hepatic failure and agranulocytosis; generally reserved for selected situations.
Mechanism of action: Propylthiouracil ballicule
