Selected Anti-Aromatase Agents/Estrogens Interactions

This information is generalized and not intended as specific medical advice. Consult your healthcare professional before taking or discontinuing any drug or commencing any course of treatment.

Medical warning:

Severe. These medicines may interact and cause very harmful effects and are usually not taken together. Contact your healthcare professional (e.g. doctor or pharmacist) for more information.

How the interaction occurs:

Anti-aromatase fight breast cancer by lowering estrogen levels. Taking estrogen may decrease the effectiveness of these medicines.

What might happen:

Your anti-aromatase agent may not work against your breast cancer.

What you should do about this interaction:

Let your healthcare professionals (e.g. doctor or pharmacist) know right away that you are taking these medicines together. Your doctor may want to change your medicines.Your healthcare professionals may already be aware of this interaction and may be monitoring you for it. Do not start, stop, or change the dosage of any medicine before checking with them first.

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  • 2.Arimidex (anastrozole) UK summary of product characteristics. AstraZeneca UK Ltd July, 2011.
  • 3.Arimidex (anastrozole) US prescribing information. AstraZeneca Pharmaceuticals LP May, 2013.
  • 4.Femara (letrozole) Canadian prescribing information. Novartis Pharmaceuticals Canada Inc. April, 2014.
  • 5.Femara (letrozole) UK summary of product characteristics. Novartis Pharmaceuticals Corporation May, 2012.
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