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Propylthiouracil Pregnancy and Breastfeeding Warnings

Medically reviewed on Mar 14, 2018

Propylthiouracil Pregnancy Warnings

This drug should be used during pregnancy only if the benefit outweighs the risk.

AU TGA pregnancy category: C
US FDA pregnancy category: D

-The lowest effective dose should be used.

-In pregnant women with untreated or inadequately treated Graves' disease, there is an increased risk of maternal heart failure, spontaneous abortion, preterm birth, stillbirth, and fetal or neonatal hyperthyroidism.
-If this drug is used during pregnancy, or if the patient becomes pregnant while taking this drug, the patient should be warned of the rare potential hazard to the mother and fetus of liver damage.
-Because propylthiouracil crosses placental membranes and can induce goiter and cretinism in the developing fetus, it is important that a sufficient, but not excessive, dose be given during pregnancy.
-The thyroid dysfunction diminishes in many women as as the pregnancy proceeds; consequently a reduction of dosage may be possible.
-In some instances, antithyroid therapy can be discontinued several weeks or months prior to delivery.
-this drug may be the preferred agent during the first trimester of pregnancy because methimazole may be associated with the rare development of fetal abnormalities.
-Since this drug may cause maternal hepatotoxicity, it may be preferable to switch to methimazole for the second and third trimesters of pregnancy.
-This drug crosses the placenta and in high doses may cause fetal goiter and hypothyroidism; therefore, the lowest possible dose should be given and thyroid function monitored every 4 to 6 weeks to maintain optimum control.

AU TGA pregnancy category C: Drugs which, owing to their pharmacological effects, have caused or may be suspected of causing, harmful effects on the human fetus or neonate without causing malformations. These effects may be reversible. Accompanying texts should be consulted for further details.

US FDA pregnancy category D: There is positive evidence of human fetal risk based on adverse reaction data from investigational or marketing experience or studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks.

See references

Propylthiouracil Breastfeeding Warnings

-This drug had been considered the antithyroid drug of choice during lactation; however, recent findings that the rates of liver injury higher with propylthiouracil (PTU) than with methimazole may alter this judgement. Some experts now recommend that methimazole be considered the antithyroid drug of choice in nursing mothers.
-No cases of PTU-induced liver damage have been reported in breastfed infants and it is unknown if the small amounts of the drug in breastmilk can cause liver damage.
-The drug or breastfeeding should be discontinued if liver toxicity is suspected.
-Only small amounts of PTU pass into breastmilk and infant thyroid suppression does not occur with usual maternal dosages.
-Taking doses right after nursing and waiting for 3 to 4 hours before nursing again should minimize the infant dosage.
-Rarely, agranulocytosis or liver toxicity might occur, and the infant should be watched for signs of infection and liver disease (e.g., bruising, jaundice).
-Monitoring of infant complete blood count and differential is advisable if there is a suspicion of drug induced blood dyscrasias.
-Some experts recommend routine monitoring of the breastfed infant thyroxine (T4) and thyrotropin (TSH) during maternal use of this drug; however, no case of thyroid function alteration has been reported among infants exposed to PTU via breastmilk.

UK, US: Benefit should outweigh risk.
AU: Use should be avoided.

Excreted into human milk: Yes

See references

References for pregnancy information

  1. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0
  2. "Product Information. Propylthiouracil (propylthiouracil)." Lederle Laboratories, Wayne, NJ.
  3. Pharmaceutical Society of Australia "APPGuide online. Australian prescription products guide online. Available from: URL:" ([2006]):

References for breastfeeding information

  1. Pharmaceutical Society of Australia "APPGuide online. Australian prescription products guide online. Available from: URL:" ([2006]):
  2. "Product Information. Propylthiouracil (propylthiouracil)." Lederle Laboratories, Wayne, NJ.
  3. United States National Library of Medicine "Toxnet. Toxicology Data Network. Available from: URL:" ([cited 2013 -]):
  4. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.