Last update June 14, 2023


Low Risk

Possibly safe. Probably compatible. Mild risk possible. Follow up recommended. Read the Comment.

It is an inhibitor of cyclin-dependent kinases (CDK) 4 and 6. It is used to treat advanced or metastatic breast cancer, HR+ or HER2-. It is given alone or with an aromatase inhibitor or estrogen antagonist. fulvestrant. Oral administration twice a day.

At the date of the last update we did not find any published data on its excretion in breast milk.

Its pharmacokinetic data (very high percentage of protein binding, moderately high molecular weight and very wide volume of distribution) make it highly unlikely that significant quantities will pass into breast milk.

Diarrhea, loss of appetite, infections, leukopenia, neutropenia, anemia, and hepatotoxicity are common adverse reactions.

It is known via Pharmacokinetics 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%. Plasma drug concentrations in the body are negligible after 7 T½. In general, a period of al least five half-lives may be considered a safe waiting period before returning to breastfeeding. (Anderson 2016)

Taking the longest published T½, these 5 T½ would correspond to 5 days. Meanwhile, express and discard milk from the breast regularly to maintain production.  This does not allow breastfeeding during treatment.

If it is administered during lactation, a clinical and analytical control in the infant is necessary for the possible side effects described.


We do not have alternatives for Abemaciclib.

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.

Jose Maria Paricio, Founder & President of APILAM/e-Lactancia

Your contribution is essential for this service to continue to exist. We need the generosity of people like you who believe in the benefits of breastfeeding.

Thank you for helping to protect and promote breastfeeding.

José María Paricio, founder of e-lactancia.

Other names

Abemaciclib in other languages or writings:


Main tradenames from several countries containing Abemaciclib in its composition:


Variable Value Unit
Oral Bioavail. 45 %
Molecular weight 507 daltons
Protein Binding 96 - 98 %
VD 10.7 l/Kg
pKa 10.27 -
Tmax 6 - 8 hours
18 - 25 hours


  1. Eli Lilly. Abemaciclib. DrugSummary. 2022 Full text (in our servers)
  2. EMA. Abemaciclib. Fiche técnica. 2018 Full text (in our servers)

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