Allergic Reactions

Allergic reactions happen when your body is sensitive to a specific substance. The reaction can happen when you swallow or inhale the substance or when it is applied to your skin or injected or transfused through an IV into your body.

Allergic reactions can take many forms.

Mild allergic reactions include:

• rashes
• hives
• itching
• runny or stuffy nose
• watery, itchy, red eyes

Moderate or severe allergic reactions include:

• swelling of the face, eyes, or tongue
• difficulty swallowing
• wheezing or difficulty breathing
• feeling anxious
• cramps
• nausea and/or vomiting
• dizziness
• passing out/becoming unconsciousness

Severe allergic reactions are known as anaphylaxis.

Any breast cancer medication can cause an allergic reaction:

• chemotherapy
• hormonal therapy:
  • Arimidex (chemical name: anastrozole) 
  • Aromasin (chemical name: exemestane)
  • Femara (chemical name: letrozole)
  • tamoxifen
  • Evista (chemical name: raloxifene)
  • Fareston (chemical name: toremifene)
  • Faslodex (chemical name: fulvestrant)
• targeted therapies:
  • Herceptin (chemical name: trastuzumab)
  • Tykerb (chemical name: lapatanib)
  • Avastin (chemical name: bevacizumab)
• pain medications

Antibiotics given after surgery also can cause allergic reactions.

Managing allergic reactions

If you've had allergic reactions to medicines, foods, or bee stings in the past, make sure you tell your doctor before you start treatment. Together you can discuss your risk of allergic reaction to any new medicines you're taking.

If you have an allergic reaction to a medicine, call your doctor immediately. The reaction may be mild to start, but may get worse quickly. It's important that your doctor knows right away.

If your throat starts to swell or you have difficulty breathing, CALL 911 IMMEDIATELY. If you have other allergies and have allergy medication or an EpiPen available, use it.

If you have a mild allergic reaction, you may be able to take an antihistamine such as Benadryl (chemical name: diphenhydramine). It's important to check with your doctor before you take any additional medicine. For itchy skin or rashes, calamine lotion or cold compresses can help.

Benadryl is known to reduce the effectiveness of tamoxifen. If you are taking tamoxifen, talk to your doctor about alternatives to Benadryl. For more information, please visit the Breastcancer.org Tamoxifen page.