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Propylthiouracil and carbimazole – use in pregnancy

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Health professionals are advised that the pregnancy category for both propylthiouracil and carbimazole is being changed from category C to category D. A Therapeutic Goods Administration (TGA) safety assessment found that the Product Information (PI) documents for these medicines adequately described known risks relating to congenital abnormalities in neonates and therefore no changes or additions were required. However, it was determined that category D was the appropriate category for these products.

Propylthiouracil is an antithyroid drug indicated for the total treatment of hyperthyroidism or in the treatment of the thyrotoxic patient prior to surgery or radioactive iodine therapy. It is marketed in Australia under the brand name PTU.

Carbimazole is also an antithyroid drug indicated for hyperthyroidism. It is used as a definitive therapy in induction of a permanent remission in either primary or secondary thyrotoxicosis. It is also used in preparation for thyroidectomy before and after radioactive iodine treatment. Carbimazole is marketed in Australia under the brand name Neo-Mercazole.

Reviewing a safety signal relating to congenital abnormalities for propylthiouracil and carbimazole, the TGA found that the current Australian PI documents for both medicines contained sufficient safety information under 'Section 4.6 Fertility, Pregnancy and Lactation'. Additionally, the carbimazole PI contains additional information on women of childbearing potential and pregnancy in 'Section 4.4 Special Warnings and Precautions for Use'.

However, the products were previously categorised under pregnancy category C, which is defined as 'Drugs which, owing to their pharmacological effects, have caused or may be suspected of causing, harmful effects on the human foetus or neonate without causing malformations. These effects may be reversible.'

As cases of congenital abnormalities have been reported in the post-market setting following use of these medicines, this category is no longer considered the correct pregnancy categorisation.

Category D is defined as 'Drugs which have caused, are suspected to have caused or may be expected to cause, an increased incidence of human foetal malformations or irreversible damage' and reflects the post-market experience with these medicines.

Information for health professionals

Propylthiouracil and carbimazole should not be prescribed for women of childbearing age unless, in the opinion of the physician, the potential benefits outweigh the possible risks.

What to report? You don't need to be certain, just suspicious!

The TGA encourages the reporting of all suspected adverse reactions to medicines, including vaccines, over-the-counter medicines, herbal, traditional or alternative remedies.

We particularly request reports of:

  • all suspected reactions to new medicines (look for the Black Triangle in PI and CMI documents - this symbol identifies medicines that are new or being used differently)
  • all suspected medicines interactions
  • suspected reactions causing death, admission to hospital or prolongation of hospitalisation, increased investigations or treatment, or birth defects.

Reports may be submitted:

For more information about reporting, visit www.tga.gov.au or contact the TGA's Pharmacovigilance and Special Access Branch ADR.Reports@tga.gov.au.

Disclaimer

Medicines Safety Update is aimed at health professionals. It is intended to provide practical information to health professionals on medicine safety, including emerging safety issues. The information in Medicines Safety Update is necessarily general and is not intended to be a substitute for a health professional's judgment in each case, taking into account the individual circumstances of their patients. Reasonable care has been taken to ensure that the information is accurate and complete at the time of publication. The Australian Government gives no warranty that the information in this document is accurate or complete, and shall not be liable for any loss whatsoever due to negligence or otherwise arising from the use of or reliance on this document.

© Commonwealth of Australia 2021

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Medicines Safety Update is written by staff from the Pharmacovigilance and Special Access Branch.

Editor: Dr Catherine Brogan

Deputy Editor: Mr Michael Pittman

Contributor: Mr Gilbert Yeap

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