Only 6.8% of children with "rash due to penicillin" have penicillin allergy

Although allergy to antibiotics is commonly claimed, true allergy to these drugs is often absent http://buff.ly/1tIbcTl

Delayed-onset urticarial or maculopapular rashes are frequently observed in children treated with beta-lactams. Many are labeled "allergic" without testing for penicillin allergy. The etiology of these rashes may be infectious rather than allergic.

This study population included 88 children presenting to the emergency department with delayed-onset urticarial or maculopapular rashes.

The tests included:

- acute and convalescent sera for viral screening
- throat swab
- intradermal and patch skin testing for β-lactams 2 months after presentation
- anti-β-lactam blood allergy tests (specific IgE)

All subjects underwent an oral challenge test (OCT) with the culprit antibiotic.

Results:

- 12.5% of children had positive intradermal and no positive patch tests
- 2.3% had positive blood allergy tests
- 6.8% had a positive OCT - a total of 6 children - 2 were intradermal-negative, and 4 were intradermal-positive
- most subjects had at least one positive viral study, 65.9% in the oral challenge test negative group

Beta-lactam allergy is clearly overdiagnosed because the skin rash is only rarely reproducible (6.8%) by a subsequent challenge. Viral infections may be an important factor in many of these rashes.

The oral challenge test was positive in a minority of intradermal skin test-positive subjects. Patch testing and blood testing provided no useful information.

Oral challenge tests should be considered in all children who develop a delayed-onset urticarial or maculopapular rash during treatment with a β-lactam.


Manifestations of beta-lactams hypersensitivity: MAUS (click to enlarge the image).

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

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

Mnemonics for penicillin allergy skin testing

Major penicillin determinant test detects
Majority of patients with penicillin allergy

Minor determinant test
Minorizes the risk

References:

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.
Penicillin and Cephalosporin allergy - Annals of Allergy, Asthma & Immunology, 2014 http://buff.ly/1ltZntr
Non IgE-mediated reaction to penicillin - AAAAI - Ask the Expert, 2011.
Diagnosis of Immediate Hypersensitivity to β-Lactam Antibiotics Can Be Made Safely with Current Approaches. Int Arch Allergy Immunol. 2011 Nov 1;157(3):311-317.
Testing for penicillin allergy can be done at any age. Consider testing with PrePen, Penicillin G and ampicillin. AAAAI Ask the Expert, 2012.
Image source: Penicillin nucleus, Wikipedia, GNU Free Documentation License.

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