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).
A healthcare professional should be consulted before taking any drug, changing any diet or commencing or discontinuing any course of treatment.
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.
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.
"Thyroid hormones in human milk and their influence on thyroid function of breast-fed babies." Pediatr Res 17 (1983 468-71 "Product Information. Synthroid (levothyroxine)." Abbott Pharmaceutical, Abbott Park, IL. Jansson L, Ivarsson S, Larsson I, Ekman R "Tri-iodothyronine and thyroxine in human milk." Acta Paediatr Scand 72 (1983 703-5 Hahn HB, Spiekerman AM, Otto R, Hossalla.
Australian prescription products guide online. Available from: URL: p." (2006 United States National Library of Medicine "Toxnet. Toxicology Data Network. Available from: URL: h.gov/cgi-bin/sis/htmlgen? LACT." (cited 2013 - Mizuta H, Amino N, Ichihara K, et al.
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.
-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.
Australian prescription products guide online. Available from: URL: p." (2006 "Product Information. Synthroid (levothyroxine)." Abbott Pharmaceutical, Abbott Park, IL. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0. References for breastfeeding information Moller B, Bjorkhem I, Falk O, Lantto O, Lafsson A "Identification of thyroxine in human breast milk by gas chromatography-mass spectrometry." J.
-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.
-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 Pharmaceutical Society of Australia "APPG uide online.
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.
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.
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.
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 ).
-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.
CONDITIONS OF USE: The information in this database is intended to supplement, not substitute for, the expertise and judgment of healthcare professionals. The information is not intended to cover all possible uses, directions, precautions, drug interactions or adverse effects, nor should it be construed to indicate that use of a particular drug is safe, appropriate.