Skin test for acyclovir drug allergy

Adverse drug reactions affect up to 10% of people. When drug reactions resembling allergy happen, they are called drug hypersensitivity reactions (DHRs). Drug hypersensitivity reactions may be allergic or nonallergic. Drug allergies are drug hypersensitivity reactions caused by the immune system.

Case scenario:

A 50-year-old male reported generalized pruritus and maculopapular rash after the second dose of acyclovir taken around 2014 for suspected shingles (no shingles developed). No LOC or SCARs.

He takes amlodipine and metoprolol XL for BP control.

SPT/ID test with acyclovir can be done using the following protocol:

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Acyclovir Skin Test Immediate Reaction

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Prick Test

Substance / Concentration / W/F (mm)

Saline
Histamine
Acyclovir 0.5 mg/ml

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Intradermal Test

Substance / Concentration / W/F (mm)

Saline
Histamine
Acyclovir 0.005 mg/ml
Acyclovir 0.05 mg/ml
Acyclovir 0.5 mg/ml
Acyclovir 5 mg/ml

Stock concentration: Acyclovir IV 50 mg/ml

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As a general precaution: Beta-blockers and ACE inhibitors should be stopped several days before any skin test or challenge with medications. The number of days depends of the half-life of each medication (5 half lives is the recommended period). The temporary stop in taking the medications has to be approved by the prescribing physician.

Drug allergy management in 5 steps (click to enlarge the image).

Classification of adverse drug reactions (ADR) (click to enlarge the image).

References:

Immediate allergy from valacyclovir. D. G. Ebo C. H. Bridts L. S. De Clerck W. J. Stevens. https://onlinelibrary.wiley.com/doi/full/10.1111/j.1398-9995.2008.01700.x

Delayed allergy to acyclovir revealed by lymphocyte proliferation test. Marcello Albanesi et al. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6232537

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