Propylthiouracil

PTU

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Pronunciation: proe-pil-thye-oe-YOOR-a-sil

Propylthiouracil ballicule: receptor binding, kinetics and half-life diagram — Mechanism of action: Propylthiouracil ballicule

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.

Propylthiouracil molecular structure (skeletal formula) — Molecular structure: Propylthiouracil

FDA-approved for

hyperthyroidism (~1947)

FDA label

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BOXED WARNING Severe liver injury and acute liver failure (some fatal, some requiring transplant) reported in adults and children; reserve for patients who cannot tolerate methimazole and in whom radioactive iodine or surgery are not appropriate.

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

Available strengths

tab 50 mg

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

Cost

Propylthiouracil (PTU)

What pharmacies pay · NADAC 9/30/26

Strength		#/mo	generic $/mo	CostPlus
50 mg	tab	90 TID	$24.19	offered

Generic entry2023

⚠ BOXED WARNING

Severe liver injury and acute liver failure

Classes and tags

Clinical profile

Therapeutic safety burden4 / 4

Overdose danger2 / 4

Weight-gain liability0 / 4

Sedation liability0 / 4

QT / Torsades0 / 4

Direct muscarinic antagonism0 / 4

Embryofetal risk3 / 4

Legacy pregnancy categoryUnknown / historical label unavailable

Defining liabilityPotentially fatal hepatic failure and agranulocytosis; generally reserved for selected situations.

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