Last update March 30, 2023
Very High Risk
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.
During cancer treatment, breastfeeding must be interrupted due to potentially serious side effects for the infant.
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 of breastfeeding 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 other authors. (Hale)
Its long elimination half-life and its daily administration over many months make it impossible to continue breastfeeding.
Accidental intake of a single dose does not require an interruption of breastfeeding. However, treatment should not be continued. (Schaefer 2015)
We do not have alternatives for Anastrozole.
Suggestions made at e-lactancia are done by APILAM team of health professionals, and are based on updated scientific publications. It is not intended to replace the relationship you have with your doctor but to compound it. The pharmaceutical industry contraindicates breastfeeding, mistakenly and without scientific reasons, in most of the drug data sheets.
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e-lactancia is a resource recommended by Academy of Breastfeeding Medicine - 2012 of United States of America
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