Micro & Immunology · patient case with 1 question
Two reactions to the same drug
Patient: Female, 34 years old
Chief Complaint: “I reacted to that antibiotic again, but differently this time.”
Background: Prescribed an antibiotic for an odontogenic infection. On the second day she developed diarrhoea, nausea, vomiting and a rash, and the drug was stopped. Some weeks later she was inadvertently given the same drug.
Vital Signs: BP 122/76 mmHg · HR 82 bpm · RR 16 · SpO₂ 98% on air
Findings: Two to three days after the second exposure she developed erythema and swelling of the face and lips. No urticaria, no wheeze, no stridor, no hypotension. The airway is patent and she is speaking normally.
Question 1
How should the SECOND reaction be managed?
Show answer and explanation
Correct answer: D. A topical corticosteroid
- A. Intubation is reserved for actual or threatened airway obstruction. The airway is patent and she is speaking normally.
- B. Epinephrine is the treatment for ANAPHYLAXIS, a TYPE I IgE-mediated reaction that begins within MINUTES of exposure with urticaria, angio-oedema, bronchospasm and hypotension. The TIMING here excludes it — a reaction developing over two to three days is not IgE-mediated, and there is no airway or cardiovascular involvement.
- C. Doing nothing is inappropriate on two counts: the reaction is uncomfortable and treatable, and more importantly the drug must be formally documented as an allergy so that it is never prescribed again — which is the failure that produced this second exposure.
- D. CORRECT. A reaction appearing two to three days after exposure, with erythema and swelling and no airway involvement, is a TYPE IV DELAYED (CELL-MEDIATED) HYPERSENSITIVITY — mediated by sensitised T lymphocytes and macrophages rather than by antibody, and peaking at 48 to 72 hours. Management is withdrawal of the allergen plus a TOPICAL CORTICOSTEROID for localised cutaneous or mucosal involvement, escalating to a systemic corticosteroid if the reaction is extensive. Antihistamines are of limited value because histamine is not the principal mediator.
Note: The four types, with TIMING as the usual exam discriminator. TYPE I: immediate, IgE, mast cell degranulation — anaphylaxis, urticaria, allergic rhinitis; minutes. TYPE II: antibody-mediated cytotoxic — transfusion reactions, pemphigus vulgaris, mucous membrane pemphigoid. TYPE III: immune complex — SLE, serum sickness, Arthus reaction; hours. TYPE IV: delayed cell-mediated — contact dermatitis, the tuberculin test, graft rejection, and the oral lichenoid contact reactions to amalgam and to latex gloves; days.