Last update: Jan. 15, 2019
Very unsafe. Contraindicated.
Use of an alternative or cessation of breastfeeding.
Anastrozole is a selective aromatase inhibitor (estrogen synthetase), which inhibits the secretion of estrogen.
Indicated in the treatment of breast cancer in postmenopause.
Oral administration once a day for prolonged periods.
Since the last update we have not found published data on its excretion in breastmilk.
Its pharmacokinetic data (low molecular weight, low protein binding and prolonged half-life) enables transfer to breastmilk in amounts which could be significant.
Pharmacokinetics show that after 3 elimination half-lives (T½) 87.5% of the drug is eliminated from the body; after 4 T½ it is 94%, after 5 T½, 96.9%, after 6 T½, 98.4% and after 7 T½ it is 99%. From 7 T½ the plasma concentrations of the drug in the body are negligible. In general, a period of at least five half-lives can be considered a safe waiting period before breastfeeding again (Anderson 2016).
According to this data, the interruption would be for a period of between 10.4 days (5 T½) to 14.6 days (7 T½) after the administration of the last dose, which coincides with the estimates of various authors: 10 days (Schaefer 2007, p 741) to 15 days (Hale 2017, p 66).
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 Anastrozole.
Suggestions made at e-lactancia are done by APILAM´s pediatricians and pharmacists, and are based on updated scientific publications.
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