Relief Allergy & Sinus Institute

Penicillin Allergy

Penicillin is a common and extremely effective antibiotic for treating several types of bacterial infections. Allergies to penicillin and similar antibiotics are typically overreported by patients and physicians alike. This overreporting unfortunately limits the use of this first ever discovered antibiotic by Dr. Alexander Fleming.

Relatives of penicillin may also be excluded as treatment options for your infections if you report a penicillin allergy. Some of these relatives include amoxicillin and the cephalosporins, such as cephalexin (Keflex). Our allergy specialists can determine if you have a true penicillin allergy.

Symptoms of Penicillin Allergy:
  • Common penicillin allergy symptoms:
    • Rash
    • Hives
    • Itching
    • Swelling
    • Fever
    • Runny nose
    • Itchy and watery eyes
    • Wheezing
    • Shortness of breath
  • Anaphylaxis:
    • Difficulty breathing
    • Difficulty swallowing
    • Wheezing
    • Nausea, vomiting, diarrhea or abdominal cramps
    • Anxiety
    • Fainting
    • Decreased blood pressure and shock
  • Delayed reactions (may occur days or weeks after taking penicillin):
    • Fever, joint pain, rash, swelling or nausea
    • Anemia or a reduction in red blood cells, which can cause fatigue and irregular heartbeats
    • Severe blistering and peeling of the skin
    • Kidney inflammation
Causes of Penicillin Allergy:

Penicillin allergy occurs when your immune system overreacts and becomes hypersensitive to the drug. Your body mistakenly reacts to the drug as a harmful substance, like bacteria or viruses. When you are exposed to penicillin, your body makes antibodies to it. The next time you take the drug, these penicillin-specific antibodies flag it, and your immune system attacks the substance. Chemicals like histamine released by your immune cells cause the symptoms associated with an allergic penicillin reaction.


Skin testing can be done to determine if you have a penicillin allergy. Testing oral penicillin at low doses (called a graded penicillin challenge) can also be performed in low-risk patients.

Treatment Options for Penicillin Allergy:
  • Avoidance – following up on your penicillin allergy testing results, we can help you avoid exposure to drugs that trigger your penicillin allergy
  • Medications – we can treat your penicillin allergy symptoms with antihistamines and corticosteroids, and anaphylaxis with an epinephrine (adrenaline) auto-injector prescription
  • Penicillin desensitization – in many cases, under lose medical supervision, allergic sensitivity can be reduced by starting with a very small penicillin dose and gradually increasing dosage over time

If you would like to learn more about how Relief Allergy & Sinus Institute can help you get your penicillin allergy under control, request an appointment today online or call (630) 513-1691.