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Isoniazid Pregnancy and Breastfeeding Warnings

Isoniazid is also known as: Nydrazid

Medically reviewed by Last updated on Oct 6, 2021.

Isoniazid Pregnancy Warnings

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

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

-Some experts recommend using this drug as a treatment for active tuberculosis during pregnancy because the benefit justifies the potential risk to the fetus.
-Preventative therapy should typically be started after delivery.
-Exposed neonates should be monitored for adverse events.

Animal studies have revealed evidence of embryocidal effects with oral administration during pregnancy. There were no teratogenic effects in animal models. There are no controlled data in human pregnancy.

AU TGA pregnancy category A: Drugs which have been taken by a large number of pregnant women and women of childbearing age without any proven increase in the frequency of malformations or other direct or indirect harmful effects on the fetus having been observed.

US FDA pregnancy category C: Animal reproduction studies have shown an adverse effect on the fetus and there are no adequate and well-controlled studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks.

See references

Isoniazid Breastfeeding Warnings

In mothers given single oral doses, average peak drug levels in breastmilk occurred at 2 to 3 hours after the dose: 2.1 mg/L (200 mg dose), 5.4 to 5.5 mg/L (300 mg dose), and 9 to 10.6 mg/L (600 mg dose).

The breastfed infants of mothers who took 300 mg once daily for at least 34 days received about 0.3% to 1.2% of the maternal-adjusted dosage of isoniazid.

This drug has been used without apparent harmful effects.

Excreted into human milk: Yes

-The US Centers for Disease Control and Prevention (US CDC) and other professional organizations state that breastfeeding should not be discouraged in patients taking this drug.
-The American Academy of Pediatrics considers this drug compatible with breastfeeding.
-The WHO classifies this drug as compatible with breastfeeding; the breastfed infant should be monitored for jaundice.
-Some experts recommend women taking this drug during breastfeeding should take pyridoxine 25 mg orally once a day, and breastfed infants treated with this drug should receive pyridoxine 1 mg/kg orally once a day.
-Drug levels should not be relied upon for prophylaxis or treatment of nursing infants.

See references

References for pregnancy information

  1. TGA. Therapeutic Goods Administration. Australian Drug Evaluation Committee "Prescribing medicines in pregnancy: an Australian categorisation of risk of drug use in pregnancy. Available from: URL:" ([1999]):
  2. "Product Information. INH (isoniazid)." Ciba Pharmaceuticals, Summit, NJ.
  3. Cerner Multum, Inc. "Australian Product Information." O 0
  4. "Product Information. Nydrazid (isoniazid)" Apothecon Inc, Princeton, NJ.
  5. "Product Information. Isoniazid (isoniazid)." Barr Laboratories Inc, Pomona, NY.

References for breastfeeding information

  1. "Product Information. Nydrazid (isoniazid)" Apothecon Inc, Princeton, NJ.
  2. Department of Adolescent and Child Health and Development. UNICEF. World Health Organization "Breastfeeding and maternal medication: recommendations for drugs in the eleventh Who model list of essential drugs. Available from: URL:" ([2003]):
  3. "Product Information. Isoniazid (isoniazid)." Barr Laboratories Inc, Pomona, NY.
  4. United States National Library of Medicine "Toxnet. Toxicology Data Network. Available from: URL:" ([cited 2013 -]):
  5. Briggs GG, Freeman RK. "Drugs in Pregnancy and Lactation. 10th ed." Philadelphia, PA: Wolters Kluwer Health (2015):
  6. "Product Information. INH (isoniazid)." Ciba Pharmaceuticals, Summit, NJ.

Further information

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