‘Useless’ skin test doesn’t catch amoxicillin allergy

"Skin tests are essentially useless as diagnostic tests," says lead author Moshe Ben-Shoshan. "This is a game changer in the way physicians assess amoxicillin allergy in children given the fact that skin tests are still the recommended screening method in hospitals." (Credit: Neil Christiansen/Flickr)

Skin tests are an ineffective way to predict if someone is allergic to amoxicillin, one of the most commonly prescribed antibiotics in children, a new study warns.

Oral provocation or challenge test, with appropriate follow up, is a more efficient and safer screening method for diagnosing non-life threatening reactions to amoxicillin in children, researchers say.

“Our study suggests that skin tests are essentially useless as diagnostic tests, and that we should go directly to the graded provocation test that is highly sensitive and specific,” says lead author Moshe Ben-Shoshan, assistant professor of pediatrics at McGill University and an allergist at the Montreal Children’s Hospital. “This is a game changer in the way physicians assess amoxicillin allergy in children given the fact that skin tests are still the recommended screening method in hospitals.”

Provocation or challenge (PC) tests are performed by gradually introducing the allergen (for example pollen, food, or drug) to the patient. They are performed in a hospital or clinic, where any serious reactions can be safely managed.

[What doctors aren’t telling parents about food allergies]

Up to 10 percent of children develop rashes while on antibiotics.

“The majority are diagnosed without further evaluation as allergic to the implicated antibiotic,” says Ben-Shoshan. “Most of the patients continue to avoid the suspect antibiotic in favor of alternatives, which may be less effective, more toxic, and more expensive.”

For the study, published in JAMA Pediatrics, researchers conducted the largest study of its kind to assess the use of a graded PC in children who presented with a rash due to a suspected amoxicillin allergy. They assessed 818 children who presented to the MCH-MUHC Allergy clinic from March 2012 to April 2015. Unlike previous studies all children had to undergo a graded PC.

Researchers observed that 94.1 percent were tolerant to the graded PC for amoxicillin. From all the study’s participants, only 17 had an immediate positive reaction to amoxicillin, and only one within this group had a positive skin test.

[8 ways to keep kids off unnecessary antibiotics]

For many antibiotics (including amoxicillin), skin tests can have a high false-negative rate. Thirty one had non-immediate reactions developing more than one hour after challenge. All non–immediate reactions were mild and manifested mainly as skin eruptions.

“Our study is the first to determine the percentage of immediate and non-immediate amoxicillin allergy in all children presenting with a suspected amoxicillin induced rash through a graded PC,” Ben-Shoshan says. “Further, we showed that in children with a negative PC, amoxicillin can be safely used in the future, although under 10 percent may develop mild cutaneous symptoms upon subsequent exposure.”

Future studies are required to assess factors associated with specific PC outcomes, and in particular researchers should investigate specific association with genetic markers to accurately determine future risk for antibiotic allergic reactions.

Source: McGill University