Medical Emergencies · patient case question
Which symptom would most likely confirm a diagnosis of penicillin allergy in Patient B?
Patient case: Adverse drug reactions in two patients
Patient: Two patients presenting the same day
Chief complaint: Patient A: “My front tooth chipped.” Patient B: “I have a really bad infection.”
History: Patient A: 52-year-old male with chronic migraines, taking amitriptyline. Patient B: 19-year-old male, asthma, smoker, documented penicillin allergy, taking albuterol.
Findings: Patient A: Ellis class I fracture of tooth #9. Patient B: acute apical abscess on tooth #3.
Show answer and explanation
Correct answer: A. Maculopapular rash
- A. CORRECT. A MACULOPAPULAR RASH is an immunologically mediated hypersensitivity reaction and is the most common true allergic manifestation of penicillin. Cutaneous findings — rash, urticaria, angioedema, pruritus — are what distinguish genuine allergy from intolerance, and they are what should be documented in the record.
- B. Vomiting is likewise an adverse gastrointestinal effect rather than hypersensitivity.
- C. Diarrhoea results from disruption of gut flora, and in its severe form indicates C. difficile colitis — a serious adverse effect, but not an allergic one.
- D. Nausea is a gastrointestinal INTOLERANCE, not an immune reaction. Recording it as an allergy is one of the commonest causes of unnecessary lifelong penicillin avoidance.
Note: This distinction has real consequences. Roughly 10 percent of people report a penicillin allergy but fewer than 1 percent have a genuine IgE-mediated one, and most who did as children lose it within a decade. Mislabelling drives patients to broader, costlier and more toxic alternatives — clindamycin among them, with its C. difficile risk. Take a proper history: what happened, how soon, and what treatment was needed.
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