Levothyroxine use while Breastfeeding
Drugs containing Levothyroxine: Synthroid, Levoxyl, Tirosint, Levothroid, Eltroxin, Euthyrox, Unithroid, L Thyroxine Roche, Oroxine, Novothyrox, Show all 16 »Levothyrox, Eutroxsig, Levotabs, Levo-T, Evotrox, Levotec
Levothyroxine Levels and Effects while Breastfeeding
Summary of Use during Lactation
Levothyroxine (T4) is a normal component of human milk. Limited data on exogenous replacement doses of levothyroxine during breastfeeding indicate no adverse effects in infants. If levothyroxine is required by the mother, it is not a reason to discontinue breastfeeding. Levothyroxine is recommended treatment for postpartum thyroiditis and tapering of the dose should be avoided when a woman is breastfeeding. Levothyroxine dosage requirement may be increased in the postpartum period compared to prepregnancy requirements patients with Hashimoto's thyroiditis.
Levothyroxine is a normal component of human milk. Although somewhat controversial, it appears that levothyroxine passes into milk poorly.
Maternal Levels. In a study of 56 mothers with thyroid disorders, 50 had hypothyroidism and were being treated with levothyroxine; 5 mothers had controlled hyperthyroidism with no medications and 1 had hyperthyroidism treated with a medication. Milk levels of thyroid hormones were free T4 4.5 ng/L, total T4 29.6 mcg/L, free T3 2.3 ng/L and total T3 0.35 mcg/L. The average milk to serum level ratios over the period were free T4 0.32 and total T4 0.3. Levels of free and total T3 and total T4 in milk were positively correlated with their respective plasma levels.
Infant Levels. Relevant published information was not found as of the revision date.
Effects in Breastfed Infants
Effects of exogenous thyroid hormone administration to mothers on their infant have not been reported. One case of apparent mitigation of cretinism in hypothyroid infants by breastfeeding has been reported, but the amounts of thyroid hormones in milk are not optimal, and this result has been disputed. The thyroid hormone content of human milk from the mothers of very preterm infants appears not to be sufficient to affect the infants' thyroid status. The amounts of thyroid hormones in milk are apparently not sufficient to interfere with diagnosis of hypothyroidism.
In a telephone follow-up study, 5 nursing mothers reported taking levothyroxine (dosage unspecified). The mothers reported no adverse reactions in their infants.
One mother with who had undergone a thyroidectomy was taking levothyroxine 100 mcg daily as well as calcium carbonate and calcitriol. Her breastfed infant was reportedly "thriving" at 3 months of age.
Effects on Lactation and Breastmilk
Adequate thyroid hormone serum levels are required for normal lactation. Replacing deficient thyroid levels should improve milk production caused by hypothyroidism. Supraphysiologic doses would not be expected to further improve lactation.
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