How Accurate Is Penicillin Skin Testing?

The immunogenic components of PCN include:

1. major determinant is benzylpenicilloyl
2. minor determinants are penicillin G (benzylpenicillin), penicilloate, and penilloate

The major determinant, conjugated to a polylysine carrier molecule, has been available as a commercial product (Pre-Pen®) since 2009.

Minor determinants, other than PCN G, are not commercially available. Some allergists synthesize their own minor determinates. AllerQuest, LLC plans to develop a minor determinant mixture.

The predictive value of a negative skin test has been reported to be 97-99%.

Testing with benzylpenicilloyl polylysine (Pre-Pen®) alone identifies up to 90% of patients likely to have IgE-mediated reactions to PCN. The addition of PCN G to the testing regimen raises the predictive value to 97%.

However, some studies have suggested that 3-30% of patients with IgE-mediated allergy to PCN may be missed by routine skin testing.

A positive PCN skin test result should rule out the use of PCN agents and other beta-lactams.

However, a negative PCN skin test does not definitively rule out the risk for an IgE-mediated reaction upon administration of the offending agent.

All patients should receive a graded challenge of the drug in settings with emergency medical support.

Hypersensitivity reactions to beta-lactam antibiotics: MAUS mnemonic 20-20-40-20%. Click here to enlarge the image.

Mnemonic for diagnosis of drug allergy: HASTA la vista (Spanish, See you later)

Assemble a list of drugs and rank them
Stop all drug candidates
Administer - dose escalation or desensitization


How Effective Is Penicillin Skin Testing? Medscape, 2010.
How Prepen Made it Back to Market: Another Twist in the Storied History of Penicillin. Gary Stadtmauer, MD.
Penicillin and Cephalosporin allergy - Annals of Allergy, Asthma & Immunology, 2014
The role of penicillin in benign skin rashes in childhood: A prospective study based on drug rechallenge. Caubet JC, Kaiser L, Lemaître B, Fellay B, Gervaix A, Eigenmann PA. J Allergy Clin Immunol. 2010 Oct 27.
Image source: Penicillin nucleus, Wikipedia, GNU Free Documentation License.

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