Last update: Jan. 15, 2020
Very unsafe. Contraindicated.
Use of an alternative or cessation of breastfeeding.
Selective inhibitor of aromatase (estrogen-synthetase), similar to anastrozole, which inhibits the secretion of estrogens.
It is used during the preoperative phase in positive hormone-receptor breast cancer in order to try breast-conserving surgery.
It is used in infertility treatments due to ovulation problems, luteal phase defects including polycystic ovarian syndrome.
Oral administration once a day for prolonged periods.
Since the last update date we have not found published data on its excretion in breastmilk.
Its pharmacokinetic data (low molecular weight, low protein binding and prolonged half-life) make transfer to milk likely in quantities that could be significant.
From pharmacokinetics it is known that after 3 elimination half-lives (T½) 87.5% of the drug is eliminated from the body; after 4 T½, 94%, after 5 T½ 96.9%, after 6 T½ 98.4% and after 7 T½ 99%. From 7 T½ plasma drug concentrations in the body are negligible. In general, a period of five half-lives can be considered a safe waiting period before returning to breastfeeding (Anderson 2016).
Expert authors recommend waiting 10 days (5 T½) after the last dose to restart breastfeeding (Hale 2017 pp. 548), fewer than the manufacturer, which advises 21 days (Novartis 2017). In the meantime, express and discard breast milk regularly.
Its long elimination half-life and its administration every 24 hours over many months make it impossible to continue breastfeeding.
We do not have alternatives for Letrozole.
Suggestions made at e-lactancia are done by APILAM´s pediatricians and pharmacists, and are based on updated scientific publications.
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