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Frequently Asked Questions
(and Answers) About Penicillin Allergy
negative. The technique is the same as the one 1. Who should be tested for penicillin
used for testing allergies to pollens and foods. The tests for penicillin allergy take about an hour Anyone who has a history of an allergic reaction to and are relatively painless.
a penicillin antibiotic is a candidate for penicillin More information on penicillin allergy testing can allergy testing. Unless there is a past history of a be found on the The American College of Allergy, previous reaction, however, testing is unnecessary. Asthma, and Immunology (ACAAI) website, If you have never reacted to penicillin, or have never taken it, testing is not indicated. 4. How should I prepare for skin
2. Why should I be tested for penicillin
testing to penicillin?
now if I do not need to take the
No complicated preparation is needed. You should, however, discontinue antihistamines and Testing might be done even if you have no need other drugs prior to testing as they may affect the to use the antibiotic immediately. Penicillin test results. If you have any doubt about a drug is a commonly used antibiotic with a variety you are taking, contact your allergist as soon as of applications. Demonstrating the absence possible prior to testing to learn what drug(s) of allergy now could be very helpful to you should be stopped, and for how long. It is best to in the future, when the need might suddenly avoid all antihistamines for 7 days prior to testing. arise. Having tests done – even if there is no Your allergist may allow some antihistamines to be current need – would save you from having to taken up until 2-3 days prior to testing if you feel have "emergency testing" if there is a need for you cannot stop them for one week. The need penicillin or cephalosporins in the future. Testing to discontinue antihistamines applies not only to may also may help prevent the use of broad oral antihistamines but also to antihistamine nasal spectrum alternative antibiotics that may increase sprays (e.g., azelastine or olopatadine). If you take the possibility of antibiotic resistant organisms. medications for depression, anxiety, or migraines, please discuss with your allergist prior to testing, 3. How is penicillin allergy testing
as some of these may need to be discontinued. done?
Testing is done with allergy skin tests. These are
performed most commonly on either the forearm or back. Tests are done by pricking and injecting the skin. A standard puncture testing device is used for the initial testing, and a syringe and needle is employed if the test using this device is Continued next page 5. Is penicillin allergy testing safe?
9. If I have a negative test to
penicillin, can I automatically take a
Yes. Skin testing to penicillin is a safe procedure. cephalosporin, if I have never had a
The test, if positive, will cause local itching and redness with swelling at the site where the test reaction to a cephalosporin?
is performed. These reactions usually resolve The vast majority of people who have negative in an hour or so. Systemic reactions such as tests to penicillin will be able to tolerate a hives can occur, but are very rare and allergists- cephalosporin. Without a previous reaction to a immunologists are prepared to treat such cephalosporin, it is not necessary to be tested or reactions. So there is no definite contraindication challenged to a cephalosporin. to these tests and, as noted, they are considered safe and effective.
10. Should patients with a history of
cephalosporin allergy who have
6. Are there alternative tests that
not subsequently taken penicillin
can be done to diagnose penicillin
or cephalosporin be tested for
cephalosporin or penicillin?
There is a blood test for penicillin allergy, but in Cephalosporin allergy is not as well-studied as general, it is not as accurate or as sensitive as the penicillin allergy, and skin testing to standardized skin test. Skin tests are considered the tests of reagents is not available. This means that all allergists do not necessarily advise the same type of evaluation. Some allergists may recommend 7. How accurate and sensitive is
skin testing to non-standardized reagents for penicillin skin testing?
cephalosporin and/or standardized penicillin testing followed by an oral challenge. Others A number of studies have documented the may suggest an oral challenge only to one or accuracy and sensitivity of skin tests for penicillin both medications, depending upon your specific allergy. Almost all patients who have negative history of reaction and the drug to which you skin tests are able to take penicillin without reacted. You will need to discuss these issues experiencing a reaction. It is generally thought with your allergist. that no more than 1 to 2 percent of patients (and perhaps even less) with a negative test will experience a mild reaction to penicillin. 11. Are people with hay fever and/or
asthma more likely to be allergic to
8. If my penicillin allergy tests are
penicillin or cephalosporin?
negative, can I immediately start
Most studies have shown that patients who taking penicillin at home?
have allergies are not at any increased risk of developing penicillin or cephalosporin allergy. The answer to this question is, in the opinion of most allergists, "no." Because of the very small percentage of patients who do react, most 12. What are the signs and symptoms
allergists, after penicillin testing is done, perform of penicillin allergy?
what is called a "challenge" in their office. As People who are allergic to penicillin usually have soon as the tests are done, or shortly thereafter, symptoms consisting of the following: the patient takes penicillin in the physician's office while under observation. The full dose can be • Hives (red welts).
given, or small but gradually increasing doses are • Swelling of parts of the body, usually the lips, administered during this period. The test usually eyes, tongue, hands, or feet. Swelling usually takes one or two hours but may take as long as occur simultaneously with the hives. four hours depending on the protocol employed by the allergist performing the challenge. After a negative challenge, you should advise all of your doctors that you are not allergic to penicillin, and that it can be used to treat future infections. Continued next page • Shortness of breath or wheezing.
• In severe reactions, fainting can occur.
Fox SJ, Park MA. Penicillin skin testing is a safe and effective tool for evaluating penicillin These symptoms usually appear shortly after the allergy in the pediatric population. J Allergy Clin ingestion of the drug. It is important to note that Immunol Pract. 2014 Jul-Aug;2(4):439-44. doi: other reactions such as a measles like rash can occur. These reactions are usually delayed in onset (several days after the initial dose). Skin testing Macy E, Ngor EW. Safely diagnosing clinically does not predict whether these delayed reactions significant penicillin allergy using only penicilloyl- poly-lysine, penicillin, and oral amoxicillin. J Allergy Clin Immunol Pract. 2013 May- 13. How often are penicillin reactions
Jun;1(3):258-63. doi: 10.1016/j.jaip.2013.02.002. Epub 2013 Apr 6.
Solensky R. The time for penicillin skin testing is We have no definitive information on the exact here. J Allergy Clin Immunol Pract. 2013 May- percentage of fatal reactions, but fatalities have 14. If I had a delayed onset, measles-like
From the ACAAI 2015 Drug Allergy and rash from penicillin, should I take
penicillin again?
Delayed reactions are more difficult to assess
and they may or may not reoccur on subsequent courses of penicillin. At times the rash may have been caused by the infection (for which the antibiotic was prescribed) and not the antibiotic. It is unlikely that if you were to receive penicillin again that you would have a life-threatening reaction. But it is possible that you could have a delayed-onset rash. Before you take penicillin again, consult an allergist and review your history. Some allergists may suggest different types of testing, or a controlled challenge, but this will depend upon your history. For more information about allergy
treatment, and to locate a board-
certified allergist in your area, visit
Insert Dr. Name Here Insert Practice Name Here Insert Practice Contact Information Here Insert Additional Information Here Board-certified allergists are specialists in diagnosing and treating allergies and asthma.
Printed with permission 2015, American College of Allergy, Asthma and Immunology

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