A 19-year-old male with a history of asthma, 3 pack-year smoking history, and penicillin allergy presents with a severe infection. Current medications include albuterol (ProAir®). Current findings show an acute apical abscess on tooth #3. What symptom would most likely confirm the diagnosis of a penicillin allergy?

Correct answer: C. Maculopapular rash

• A. INCORRECT. Nausea is a nonspecific gastrointestinal symptom that can occur with many medications and conditions. It is not characteristic of a penicillin allergic reaction and does not confirm an IgE-mediated or immune-mediated allergy.
• B. INCORRECT. Vomiting, like nausea, is a nonspecific side effect seen with many antibiotics. It reflects GI irritation, not an allergic immune response, and does not confirm penicillin allergy.
• C. CORRECT. A maculopapular rash is the most common manifestation of penicillin allergy, representing a type IV (delayed hypersensitivity) or type I (IgE-mediated) reaction. It presents as flat-to-slightly raised, red, blotchy skin lesions and is the hallmark finding confirming a true penicillin allergic reaction. Over 80% of reported penicillin allergic reactions involve skin manifestations.
• D. INCORRECT. Diarrhea is a common side effect of antibiotics due to disruption of gut flora, particularly seen with broad-spectrum agents. It does not indicate an allergic reaction to penicillin and is not confirmatory of penicillin allergy.