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Levothyroxine Pregnancy and Breastfeeding Warnings

Levothyroxine is also known as: Eltroxin, Euthyrox, Eutroxsig, Evotrox, L Thyroxine Roche, Levo-T, Levotabs, Levotec, Levothroid, Levothyrox, Levoxyl, Novothyrox, Oroxine, Synthroid, Tirosint, Unithroid

Levothyroxine Pregnancy Warnings

Use is considered acceptable. AU TGA pregnancy category: A US FDA pregnancy category: A Comments: -Thyroid replacement therapy should be maintained during pregnancy. -Patients should be monitored closely.

-This drug has been in administered during pregnancy without apparent harmful effects. -Studies in women taking this drug during pregnancy have not shown an increased risk of congenital abnormalities. Therefore, the possibility of fetal harm appears remote. This drug should not be discontinued during pregnancy and hypothyroidism diagnosed during pregnancy should be promptly treated. -Hypothyroidism during pregnancy is associated with a higher rate of complications, including spontaneous abortion, pre-eclampsia, stillbirth and premature delivery. Maternal hypothyroidism may have an adverse effect on fetal and childhood growth and development. -During pregnancy, serum T4 levels may decrease and serum TSH levels increase to values outside the normal range. Since elevations in serum TSH may occur as early as 4 weeks gestation, pregnant women taking this drug should have their TSH measured during each trimester. An elevated serum TSH level should be corrected by an increase in the dose of this drug. -Since postpartum TSH levels are similar to preconception values, the dosage should return to the pre-pregnancy dose immediately after delivery. A serum TSH level should be obtained 6 to 8 weeks postpartum. -Thyroid hormones cross the placental barrier to some extent as evidenced by levels in cord blood of athyreotic fetuses being approximately one-third maternal levels. Transfer of thyroid hormone from the mother to the fetus, however, may 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: US FDA pregnancy category A: Adequate and well-controlled studies have failed to demonstrate a risk to the fetus in the first trimester of pregnancy (and there is no evidence of risk in later trimesters).

See references

Levothyroxine Breastfeeding Warnings

-In one study, levothyroxine (thyroxine) levels in 70 milk samples from 20 euthyroid women 17 to 39 days after delivery were determined by gas chromatography-mass spectrometry (GCMS). The drug was present in milk in concentrations less than 4 ng/mL. The authors suggested that, at most, a breast-fed infant would ingest approximately 10% of the recommended dose for hypothyroid infants. -The majority of other studies have used radio immunoassay (RIA), a less specific assay, to measure thyroid hormone concentrations in human milk. Such studies have yielded significantly variable results. Earlier studies concluded that levothyroxine (thyroxine) and triiodothyronine were present in sufficient quantities to treat a hypothyroid infant. However, most subsequent studies have concluded otherwise. -The presence of thyroid hormone in breast milk does not appear to interfere with neonatal thyroid screening.

Use is considered acceptable; caution is recommended. Excreted into human milk: Yes (minimumally) Comments: -This drug is a normal component of human milk. -Limited data on use of this drug during breastfeeding indicate no adverse effects in infants. -If this drug is required by the mother, it is not a reason to discontinue breastfeeding. -This drug is recommended treatment for postpartum thyroiditis and tapering of the dose should be avoided when a woman is breastfeeding. -The dosage requirement of this drug may be increased in the postpartum period compared to prepregnancy requirements patients with Hashimoto's thyroiditis.

See references

References for pregnancy information

  1. Pharmaceutical Society of Australia "APPGuide online. Australian prescription products guide online. Available from: URL:" ([2006]):
  2. "Product Information. Synthroid (levothyroxine)." Abbott Pharmaceutical, Abbott Park, IL.
  3. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0

References for breastfeeding information

  1. Moller B, Bjorkhem I, Falk O, Lantto O, Lafsson A "Identification of thyroxine in human breast milk by gas chromatography-mass spectrometry." J Clin Endocrinol Metab 56 (1983): 30-4
  2. Pharmaceutical Society of Australia "APPGuide online. Australian prescription products guide online. Available from: URL:" ([2006]):
  3. United States National Library of Medicine "Toxnet. Toxicology Data Network. Available from: URL:" ([cited 2013 -]):
  4. "Product Information. Synthroid (levothyroxine)." Abbott Pharmaceutical, Abbott Park, IL.
  5. Mizuta H, Amino N, Ichihara K, et al. "Thyroid hormones in human milk and their influence on thyroid function of breast-fed babies." Pediatr Res 17 (1983): 468-71
  6. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0
  7. Jansson L, Ivarsson S, Larsson I, Ekman R "Tri-iodothyronine and thyroxine in human milk." Acta Paediatr Scand 72 (1983): 703-5
  8. Hahn HB, Spiekerman AM, Otto R, Hossalla DE "Thyroid function tests in neonates fed human milk." Am J Dis Child 137 (1983): 220-2

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