Pharmacology · patient case question
A patient reports 'an allergy to penicillin.' Which reported symptom best supports a TRUE allergy?
Patient case: An Extraction, a Block, and a Drooping Eyelid
Patient: 45-year-old female
Chief Complaint: Extraction of tooth #19.
Background: No medical history of note. No known drug allergies, though she reports her mother 'reacts to penicillin.'
Medications: None
Vital Signs: BP 120/76 mmHg · HR 74 bpm · RR 16 · T 98.4°F
Findings: An inferior alveolar nerve block is administered. Within minutes she is unable to close her right eye and the right corner of her mouth droops. Lip and tongue numbness on that side is profound.
Show answer and explanation
Correct answer: D. A rash or urticaria
- A. Diarrhoea is an extremely common adverse effect of amoxicillin and reflects disruption of the gut flora, not allergy. Antibiotic-associated diarrhoea, including Clostridioides difficile colitis, is a toxicity issue.
- B. Vomiting is likewise an adverse effect rather than an allergic phenomenon.
- C. Nausea is a common ADVERSE EFFECT, a direct gastrointestinal irritation, not an immune reaction.
- D. CORRECT. A RASH — particularly urticaria, and especially with pruritus, angioedema, wheeze or hypotension — is an IMMUNE-MEDIATED response and supports a true allergy. IgE-mediated reactions typically appear within an hour of the dose. Roughly 90% of patients who report a penicillin allergy are found on testing NOT to be allergic, so a careful history matters enormously.
Note: The distinction is clinically consequential: labelling a patient penicillin-allergic on the basis of childhood nausea pushes them toward clindamycin and broad-spectrum alternatives, which carry higher rates of C. difficile and resistance. Ask specifically: what happened, how soon after the dose, and did it need treatment?