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.
Many people who report having a penicillin allergy don't have a true allergy. They may have had a reaction to penicillin, such as certain types of rash, but not all reactions are allergies. Penicillin allergy symptoms include:
When to see a doctor
If you have less severe reactions after taking penicillin, talk to your doctor. If possible, see your doctor when the allergic reaction is occurring. This will aid in making a diagnosis.
A drug rash usually starts within two weeks of taking a new medication and begins as discrete red spots that spread, covering large areas of the body. ...
Penicillin allergy occurs when your immune system responds to the drug as if it were a harmful substance instead of a helpful remedy. Your immune system triggers certain cells to produce immunoglobulin E (IgE) antibodies to fight the component of penicillin to which you're allergic (allergen). Chemicals released by your immune cells can cause the signs and symptoms associated with an allergic reaction.
Penicillin belongs to a family of drugs called beta-lactam antibiotics. These drugs include penicillin and amoxicillin, which are relatively inexpensive and effective at treating many common bacterial infections. Such infections include skin, ear, sinus and upper respiratory infections.
Taken orally or injected, penicillin works by stopping the growth of bacteria in your body. Several varieties of penicillin exist, and each targets a different infection in a different part of your body. You may have heard of some of the other drugs in the penicillin family, including:
If you're allergic to one type of penicillin, you're at risk of being allergic to all penicillin-related antibiotics. Some people allergic to penicillin may also be allergic to cephalosporins, a class of antibiotics closely related to penicillin.
You aren't born allergic to penicillin, but you can develop penicillin allergy once you've been exposed to the drug. After that, re-exposure to penicillin or related antibiotics can trigger an allergic reaction, sometimes more severe than the reaction to the first exposure.
It isn't clear why some people develop penicillin allergies while others don't. However, certain people seem to be at greater risk of developing a penicillin allergy than others are.
You may be at higher risk if:
Preparing for your appointment
You're likely to start by seeing your family doctor or a general practitioner. However, in some cases when you call to set up an appointment, you may be referred immediately to an allergist, a doctor who specializes in allergies.
To be sure you get the information you need, it's good to be prepared for your appointment. Here's some information to help you get ready for your appointment, and what to expect from your doctor.
What you can do
Preparing a list of questions before your appointment will help you make the most of your time with your doctor. List your questions from most important to least important. For penicillin allergy, some basic questions to ask your doctor include:
In addition to the questions that you've prepared, don't hesitate to ask for clarification of anything you don't understand.
What to expect from your doctor
What you can do in the meantime
Tests and diagnosis
Your doctor will want to know about your past reactions to penicillin and may examine you to identify or exclude other medical problems. Unless you require penicillin — either because it's the only effective antibiotic for a life-threatening condition or because you're allergic to other antibiotics and have few treatment options — your doctor may prescribe another antibiotic.
Your doctor may recommend you be tested for penicillin allergy if:
Because of the risk of anaphylaxis, testing for penicillin allergy should only be done by an allergist in a hospital or doctor's office.
If the skin tests to penicillin are negative, your doctor may recommend penicillin or a related antibiotic. If the skin test to penicillin is positive, most likely your doctor will recommend that you continue to avoid penicillin and related antibiotics.
Treatments and drugs
If you have an allergic reaction after taking an antibiotic in the penicillin family, you should:
Treatment for signs and symptoms you develop during an allergic reaction to penicillin depends on what kind of reaction you have.
Lifestyle and home remedies
If you think you've had reactions to penicillin in the past, be sure to tell your doctor and other medical professionals, including your dentist. Let your doctor know about any new reactions you notice when taking your medication.
If your doctor determines that you're allergic to penicillin, it's a good idea to wear a medical alert bracelet that describes your allergy. You might also want to carry an alert card in your wallet or purse. These items are available over-the-counter at most drugstores or can be purchased on the Internet.
The best way to avoid an allergic reaction to penicillin is to avoid penicillin and similar antibiotics altogether. If you require an antibiotic, your doctor will work with you to find one you can tolerate. When a doctor or other medical professional prescribes an antibiotic, be sure to double-check that it's not in the penicillin family.
During the desensitization process, you receive small but gradually increasing doses of penicillin orally or intravenously. Because desensitization can trigger an allergic reaction, it's attempted only in a controlled setting, usually a hospital, by a doctor trained in the technique, and only when penicillin is absolutely necessary. Your desensitization lasts only as long as you continue taking penicillin. If you stop and then need to take penicillin again later, you'll need to go through the desensitization process again.
The process of desensitization generally takes one to two days. However, it doesn't work in all cases.
Last Updated: 2009-12-18
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