What is the skin test for an allergy to penicillin (antibiotic)?

From the Guidelines

Skin testing for penicillin allergy is recommended for patients with a history of penicillin allergy before administering penicillin antibiotics, and the test involves applying small amounts of penicillin metabolites to the skin and observing for allergic reactions, with a positive reaction typically showing a wheal of at least 3mm with surrounding erythema within 15-20 minutes 1.

Key Points

• The standard protocol includes major and minor determinant mixtures, with Pre-Pen (benzylpenicilloyl polylysine) being the only FDA-approved major determinant.
• The test begins with a skin prick test, and if negative, proceeds to intradermal testing.
• Negative skin tests indicate that the patient can safely receive penicillin with a low risk (less than 1%) of an immediate allergic reaction.
• The negative predictive value of penicillin skin testing is >95% 1.

Testing Procedure

• Full-strength reagents are applied by the prick/puncture technique, and if these results are negative, intradermal testing should be performed.
• Antibiotic intradermal skin testing is most reproducible when fluid is drawn up by first filling the syringe with a larger volume (0.05-0.07 mL) and expelling the excess fluid and air bubbles to obtain 0.02 mL, then injecting to produce a baseline 3-5 mm bleb.
• A positive test is defined by the size of the wheal, which should be 3 mm or greater than that of the negative control for either prick/puncture or intradermal tests and be accompanied by a 5 mm or greater flare 1.

Importance of Testing

• Approximately 90% of patients reporting penicillin allergy are not truly allergic, and avoiding penicillin unnecessarily can lead to the use of broader-spectrum antibiotics, increased healthcare costs, and potentially worse clinical outcomes.
• Skin testing is valuable in identifying patients who can safely receive penicillin, and elective challenge with the offending penicillin is recommended after negative skin test results to reassure the patient and clinicians of the safety of using penicillins and other beta-lactam antibiotics 1.

From the FDA Drug Label

Prior to treatment, a hypersensitivity test should be performed if possible

The skin test for an allergy to penicillin (antibiotic) is a hypersensitivity test that should be performed prior to treatment if possible.

• This test is used to assess the patient's sensitivity to penicillin and to minimize the risk of an allergic reaction.
• The test is particularly important for patients with a history of penicillin hypersensitivity or atopic individuals 2.
• It is recommended to exercise caution when administering penicillin to patients with a history of allergy, asthma, or urticaria 2.

From the Research

Skin Test for Penicillin Allergy

The skin test for an allergy to penicillin, an antibiotic, involves several steps and reagents.

• The test typically includes skin testing with penicilloyl-poly-lysine and native penicillin G, as well as an oral amoxicillin challenge if the skin test is negative 3, 4.
• Skin testing with major and minor determinants of benzylpenicillin, such as benzylpenicilloyl polylysine (PPL) and minor determinant mixture (MDM), is also recommended 5, 6.
• The use of alternative reagents, such as those synthesized in a laboratory or the radioallergosorbent test (RAST), may be considered in certain situations 6, 7.
• It is essential to note that a negative skin test result does not entirely exclude the possibility of hypersensitivity, and further testing, such as RAST, may be necessary 7.

Reagents and Testing Procedures

• Penicilloyl-poly-lysine and native penicillin G are commonly used reagents for skin testing 3, 4.
• Benzylpenicilloyl polylysine (PPL) and minor determinant mixture (MDM) are also used for skin testing 5.
• The radioallergosorbent test (RAST) can be used as a complementary test for individuals with a negative skin test result 7.
• Oral amoxicillin challenge is used to confirm or refute clinically significant IgE-mediated penicillin allergy if the skin test is negative 3, 4.

Interpretation of Results

• A positive skin test result indicates a potential allergy to penicillin 3, 5.
• A negative skin test result does not entirely exclude the possibility of hypersensitivity, and further testing may be necessary 7.
• The results of the skin test and oral amoxicillin challenge should be interpreted together to determine the presence or absence of a clinically significant IgE-mediated penicillin allergy 3, 4.