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Penicillin Allergy


Disease: Penicillin Allergy Penicillin Allergy
Category: Allergies
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Disease Definition:

Penicillin allergy is an overreaction by your immune system to penicillin and related antibiotics. If you have a penicillin allergy, your reaction to taking the antibiotic may range from a rash to anaphylaxis, a potentially life-threatening condition.

Penicillin allergy is the most common drug allergy. Penicillin antibiotics are widely prescribed for bacterial infections such as strep throat. However, not all unfavorable reactions to penicillin are a true penicillin allergy.

It isn't clear why some people develop penicillin allergy. Once you've had an allergic reaction to penicillin, the simplest way to prevent penicillin allergy is to avoid penicillin and related antibiotics. Penicillin allergy is the most common drug allergy; it is an overreaction of the immune system to penicillin and associated antibiotics. When having a penicillin allergy and taking the antibiotics, the allergic person may have reactions that range from a rash to anaphylaxis, which is a life-threatening condition. These antibiotics are widely prescribed for bacterial infections like strep throat. However, not all unfavorable reactions to penicillin are necessarily true penicillin allergy.

The exact cause of developing penicillin allergy is still not known. The easiest way to prevent penicillin allergy once someone’s discovered having it might be avoiding the penicillin and all sorts of related antibiotics.

Work Group:

Prepared by: Scientific Section

Symptoms, Causes


Not all reported penicillin allergy cases mean having a true allergy. A person might have had a reaction to penicillin, like some sorts of rash, but not necessarily all reactions are allergies. Symptoms for penicillin allergy include the following:


  • Itchy skin
  • Wheezing
  • Hives
  • Swollen lips, tongue or face (angioedema)
  • Rash


A life-endangering analphylactic reaction is the most serious of all allergic reactions to penicillin. In highly sensitive people, anaphylactic reactions begin right after being exposed to penicillin. Signs and symptoms include:


  • Wheezing
  • Dizziness
  • Rapid or weak pulse
  • Drop in blood pressure
  • Difficulty breathing
  • Swelling of the throat or tongue
  • Loss of consciousness

When someone is having an anaphylactic reaction, medical care should be sought immediately. When having less severe reactions after taking penicillin however, talking to the doctor would be sufficient. To make the diagnosis easier, the patient could try to see the doctor while still having the allergic reaction.


When the immune system takes the medication to be a harmful substance rather than a helpful remedy, penicillin allergy occurs. To fight the element of penicillin to which the person is allergic (allergen), his/her immune system triggers certain cells to produce immunoglobulin E (IgE) antibodies. Immune cells release chemicals that lead to signs and symptoms related to an allergic reaction.
Penicillin is categorized in a family of medications known as beta-lactam antibiotics. These medications include penicillin and amoxicillin and are relatively inexpensive and effective at treating numerous common bacterial infections. Ear, sinus, skin and upper respiratory infections are all included in these bacterial infections. Penicillin, either taken orally or injected, is most effective at preventing the bacteria from growing in the body. Many different sorts of penicillin are available, and each one targets a different infection in a different part of the body. The following medications are popular in the penicillin family:


  • Penicillin G
  • Penicillin V
  • Piperacillin and tazobactam
  • Amoxicillin
  • Dicloxacillin
  • Ampicillin

When someone is allergic to one kind of penicillin, they might be at risk of being allergic to all penicillin-related antibiotics. Certain people who are allergic to penicillin might also be allergic to cephalosporins, a category of antibiotics closely related to penicillin. Penicillin allergy isn’t congenital (present at birth); rather, it develops when a person is exposed to the medication. After that, re-exposure to penicillin or related antibiotics could trigger an allergic reaction, occasionally more severe than the first reaction.
Penicillin allergies do not have a certain cause of occurrence. Yet, some people appear to be at a higher risk of developing a penicillin allergy than others. Some of the factors that increase this risk include:


  • Having HIV/AIDS
  • Having cystic fibrosis
  • Being between the ages of 20 and 49
  • Having had allergic reactions to penicillin or another medication in the past
  • Having taken penicillin frequently





When having an allergic reaction after taking a penicillin-related antibiotic, one should:


  • Stop taking the medication and ask for other antibiotics
  • Avoid using penicillin in the future


Depending on what kind of reaction a person develops, signs and symptoms appearing throughout an allergic response could determine which treatment is more suitable.

Rashes or hives:
When treated with antihistamine like diphenhydramine, rashes or hives may improve. Oral or injected corticosteroids could be needed for more severe cases.

This is a life-endangering, as well as the most rare and serious allergic reaction to a medication. When it occurs, an injection of epinephrine (adrenaline) is needed in addition to emergency care to support breathing and keep blood pressure at level.


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