It might be resulting from something else.
Any individual hive shouldn’t last more than 24 hours.
Other symptoms of erythema multiforme can includefever, joint aches,mouth sores, and red eyes.
Verywell / JR Bee
Is It a Penicillin Allergy?
Unfortunately, penicillin allergies can be harder to diagnose than most parents can imagine.
There are also some drug reactions that can cause rashes that are not antibody-mediated.
More severe reactions may need to be treated with steroids and/orepinephrine injection.
A pediatric allergist can help to figure out if your child is really allergic to penicillin.
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Is this patient allergic to penicillin?
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