Tamoxifen Pregnancy and Breastfeeding Warnings
Tamoxifen Pregnancy Warnings
Tamoxifen has been assigned to pregnancy category D. Animal studies of doses at or below human doses have revealed evidence of fetotoxicity, lower incidence of implantation, and an increased incidence of low birth weight. There are no controlled data in human pregnancy. However, the manufacturer reports spontaneous abortions, birth defects, fetal deaths, and vaginal bleeding associated with tamoxifen use during pregnancy. Tamoxifen should only be given during pregnancy when benefit outweighs risk. Tamoxifen has been studied in the treatment of male infertility. While some degree of improvement in sperm concentration has been reported, there is generally no change in the sperm's motility. No convincing evidence of efficacy for the use of tamoxifen in treating male infertility has been reported. This is primarily because tamoxifen has not been shown to be effective in increasing the rate of contraception.
A single case of Goldenhar's syndrome (oculoauriculovertebral dysplasia) in an infant exposed to tamoxifen during the first 26 weeks of gestation has been reported; causality is unknown. A case of ambiguous genitalia in an infant exposed to tamoxifen in utero has also been reported.
Tamoxifen Breastfeeding Warnings
One study (n=150) has reported that tamoxifen was very effective in preventing milk secretion and breast engorgement when administered within two hours after delivery. In this study, no side effects were reported.
There are no data on the excretion of tamoxifen and its metabolites into human milk. However, tamoxifen administration reduces serum prolactin levels following multiple doses and suppresses prolactin release in response to breast stimulation. The manufacturer has stated that because of the potential for serious adverse reactions in nursing infants from tamoxifen, women taking tamoxifen should not breast-feed.
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