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Penicillin Allergy Testing

Testing for Penicillin Allergy

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Updated May 16, 2014

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Penicillin Allergy Testing

Intradermal skin testing involves the injection of an allergen extract under the skin to raise a "bubble" under the skin, which is then "read" after 15-20 minutes, with a positive reaction resulting in a raised, red, itchy bump.

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Penicillin Allergy: A Common Problem

Penicillin and related antibiotics are some of the oldest and most commonly used antibiotics available. They are active against a wide variety of infections, are inexpensive, and are generally well tolerated. Unfortunately, penicillin allergy is very common, with 10% of the population reporting an allergy to this medication. Studies show, however, that when people who report being allergic to penicillin are tested for the allergy, nearly 90% are not allergic, and are able to take the medicine just fine. That's often because this allergy is often temporary.

Testing for penicillin allergy is available, is a relatively simple procedure, and most often leads to a person who thought they were allergic to penicillin to find out that they are not actually allergic to the antibiotic, or are no longer allergic.. Most allergists have the ability to perform penicillin allergy testing.

Avoiding Penicillin Can Lead to Other Problems

Most people with a penicillin allergy simply avoid taking penicillin and related antibiotics, as there are a wide variety of other antibiotics to take should an infection occur. But is this the right approach to take? Various studies show that when a person is labeled as penicillin allergic, numerous complications may arise as a result of being given other antibiotics.

First, the cost of taking non-penicillin antibiotics goes up dramatically. Studies show that the average cost of antibiotics in a person with a penicillin allergy is 63% higher than in those without a penicillin allergy. Second, the use of non-penicillin antibiotics, especially in a hospital setting, places a person at risk for the development of infections by antibiotic-resistant bacteria, such as vancomycin resistant enterococcus (VRE). Lastly, the use of non-penicillin antibiotics may also put a person at higher risk of developing Clostridium difficile colitis, a dangerous infection of the intestines caused by the use of strong antibiotics.

The use of penicillin allergy testing in people reporting a history of penicillin allergy has been shown in numerous studies to cut the use of stronger, more expensive antibiotics by more than half. Other studies have shown that through the use of penicillin allergy testing, the cost of antibiotics to treat infections drops by more than 30%.

Penicillin Is Good at Causing Allergic Reactions

Penicillin is able to easily trigger allergic reactions in people due to its ability to bind to proteins in the blood and on cells in the body in order to stimulate the immune system. This process, called haptenization, leads to the body’s immune system being better at recognizing the penicillin as an allergen. Sensitization, or the development of allergic antibodies, to penicillin then occurs, which can lead to allergic reactions when a person is exposed to penicillin in the future.

Components of the Penicillin Allergy Test

Penicillin allergy testing involves the use of various skin testing techniques, including prick skin testing and intradermal skin testing, to penicillin and penicillin metabolites. Most allergy physicians perform skin testing with penicillin G (an injectable form of penicillin that is in liquid form), Pre-Pen (benzylpenicilloyl polylysine) - the major metabolite of penicillin after the body breaks down the drug, and a minor determinant mixture (MDM) containing other "minor" metabolites.

MDM is not available commercially available at this time, although some allergists -- such as those working in university settings -- will make a "homemade" version. Penicillin testing that includes the use of MDM adds to the accuracy of the testing.

Allergy blood tests are also available for penicillin allergy testing, but they are not very accurate, and generally should not be used as a substitute for penicillin allergy skin testing.

How Penicillin Allergy Testing Is Performed

Generally, prick skin testing is performed first, which is able to identify the most sensitive penicillin-allergic people. If prick skin testing is positive, then the person is considered to be allergic to penicillin, and no additional testing is done. If prick testing is negative, then intradermal skin testing is performed with the same materials. Intradermal skin testing identifies many more people with penicillin allergy, but is potentially dangerous in the most sensitive people. This is the reason why prick skin testing is performed first.

If skin testing to penicillin and related metabolites is negative using both prick and intradermal techniques, then the chance of the person being allergic to penicillin is less than 5%. Most physicians then feel comfortable prescribing penicillin and penicillin-related antibiotics to that person, although some physicians (including myself) still recommend giving the first dose of penicillin under medical supervision, and monitoring for an hour or two. I even go a step further, and perform an oral challenge to a penicillin antibiotic (typically amoxicillin) under medical supervision to ensure that the person can tolerate the antibiotic.

If any of the above mentioned tests are positive, then a person should consider himself or herself allergic to penicillin. In this situation, penicillin and related antibiotics should be avoided, unless there is a special need for penicillin – and the use of other antibiotics won’t be sufficient. Desensitization to penicillin can be performed, sometimes in a medical office setting, but usually in a hospital setting, so that a person can tolerate a course of penicillin. It is important to realize, however, that desensitization only lasts for a few days, so desensitization does not lead to an allergy cure, but only a short-term tolerance of the medication.

Read more about what antibiotics should be avoided with penicillin allergy.

Sources:

Fox S, Park M. Penicillin Skin Testing in the Evaluation and Management of Penicillin Allergy. Ann Allergy Asthma Immunol. 2011;106:1-7.

Nugent JS, Quinn JM, McGrath CM, et al. Determination of the Incidence of Sensitization After Penicillin Skin Testing. Ann Allergy Asthma Immunol. 2003;90:398-403.

Pre-Pen Package Insert. ALK-Abello. Website Accessed June 27, 2013.

DISCLAIMER: The information contained in this site is for educational purposes only, and should not be used as a substitute for personal care by a licensed physician. Please see your physician for diagnosis and treatment of any concerning symptoms or medical condition.

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