Skip to content
ClinCalc Pro
Menu
Calculators Drugs Pathways AI Dx Donate Get the App
Thionamide Antithyroid Agent

Propylthiouracil (PTU)

Brand names: Propylthiouracil (generic)

Used in: Thyroid Disorders

Propylthiouracil is an antithyroid drug used for hyperthyroidism, particularly in the first trimester of pregnancy and in thyroid storm, where it is preferred over carbimazole.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.

US labelling (FDA)

Reference — US labelling, may differ from UK

DOSAGE AND ADMINISTRATION Propylthiouracil is administered orally. The total daily dosage is usually given in 3 equal doses at approximately 8-hour intervals. Adults The initial dose is 300 mg daily. In patients with severe hyperthyroidism, very large goiters, or both, the initial dose may be increased to 400 mg daily; an occasional patient will require 600 to 900 mg daily initially. The usual maintenance dose is 100 to 150 mg daily. Pediatric Patients Propylthiouracil is generally not recommended for use in the pediatric patient population except in rare instances in which other alternative therapies are not appropriate options. Studies evaluating appropriate dosing regimen have not been …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2023-12-26. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Clinical monograph

How it works

It inhibits thyroid peroxidase (reducing thyroid hormone synthesis) and, at higher doses, the peripheral conversion of T4 to active T3.

Prescribing in practice

  • It carries a higher risk of severe hepatotoxicity than carbimazole, so it is reserved for specific situations.
  • Agranulocytosis is a key risk — advise stopping and seeking an urgent full blood count for sore throat, fever or mouth ulcers.
  • ANCA-associated vasculitis is a recognised rare effect.

Monitoring

Monitor thyroid function to titrate the dose, and liver function; check FBC urgently with infection symptoms.

Counselling the patient

  • Stop it and get an urgent blood test if you develop a sore throat, fever or mouth ulcers.
  • Report yellowing of the skin or eyes, or dark urine.

Evidence & guidelines

An antithyroid drug reserved for first-trimester pregnancy and thyroid storm, balanced against its hepatotoxicity.

Reference: MHRA Drug Safety Update 2010; British Thyroid Association Guidelines; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

Pathways