BSN Tracker

propylthiouracil

Brand: PTU

⚠ BBW Prototype: methimazole
Drug Class: thionamide
Drug Family: antithyroid
Subclass: antithyroid agent
Organ Systems: endocrine

Mechanism of Action

Inhibits thyroid peroxidase, blocking oxidation of iodide and coupling of iodotyrosines to form T3 and T4. Uniquely also inhibits peripheral 5'-deiodinase, reducing conversion of T4 to the more active T3 — this additional mechanism makes PTU the preferred agent in thyroid storm for rapid hormone reduction.

thyroid peroxidase (TPO)5'-deiodinase

Indications

  • hyperthyroidism (Graves' disease)
  • thyroid storm (drug of choice)
  • pregnancy hyperthyroidism (first trimester preferred over methimazole)

Contraindications

  • PTU-induced hepatotoxicity history

Adverse Effects

Common

  • rash
  • pruritus
  • arthralgia
  • nausea
  • headache

Serious

  • agranulocytosis (0.5%)
  • hepatotoxicity (including fatal fulminant hepatic failure)
  • ANCA-positive vasculitis
  • lupus-like syndrome

Pharmacokinetics (ADME)

Absorption oral; rapidly absorbed; bioavailability ~80–90%
Distribution concentrated in thyroid gland; minimal protein binding
Metabolism hepatic glucuronidation; does NOT cross placenta as readily as methimazole
Excretion renal
Half-life 1–2 hours
Onset days to weeks (thyroid stores must deplete)
Peak hours
Duration continuous dosing required
Protein Binding ~75–80%
Vd 0.4 L/kg

Drug Interactions

Drug / Agent Mechanism Severity
warfarin PTU reduces vitamin K clotting factor synthesis via hyperthyroidism control; monitor INR major
digoxin as hyperthyroidism resolves, digoxin levels rise; dose adjustment may be needed moderate

Nursing Considerations

  1. Monitor CBC with differential weekly for the first 3 months; instruct patient to report fever, sore throat, or mouth sores immediately — these may indicate agranulocytosis.
  2. Monitor LFTs closely; serious and fatal hepatic failure has occurred; discontinue at first signs of hepatic injury (jaundice, abdominal pain, dark urine).
  3. PTU is preferred in the first trimester of pregnancy over methimazole (which is associated with aplasia cutis in early pregnancy).
  4. Administer in 3 divided doses every 8 hours; use consistently with respect to meals.

Clinical Pearls

  • PTU is the drug of choice in thyroid storm because its inhibition of 5'-deiodinase prevents peripheral T4→T3 conversion, rapidly reducing thyroid hormone bioactivity — methimazole lacks this effect.
  • The FDA issued a black box warning for hepatotoxicity in 2010; PTU should now be reserved for specific indications (thyroid storm, first-trimester pregnancy, methimazole allergy) rather than as a routine first-line agent.

Safety Profile

Pregnancy use-with-caution
Lactation use-with-caution
Renal Adjustment Not required
Hepatic Adjustment Required
TDM Not required

Concordance Terms

Cross-referenced clinical concepts — click any term to see all content where it appears.

Hyperthyroidism (Graves' Disease) Pregnancy Hyperthyroidism (first Trimester Preferred Over Methimazole) Thionamide Thyroid Storm (drug Of Choice)
← Back to Medications