In a 74‑year‑old woman who developed a new facial rash on the cheeks one day after her hernia surgery, what is the most likely cause and how should it be managed?

Postoperative Drug Reaction (Most Likely Perioperative Antibiotic Allergy)

This is most likely a drug-induced cutaneous reaction from perioperative antibiotics (typically cefazolin), and you should immediately discontinue the suspected culprit drug, document the reaction with serum tryptase if available, and refer for formal allergy testing before any future surgeries.

Most Probable Diagnosis

The timing (day 1 post-surgery) and distribution (facial/cheeks) strongly suggest a drug-induced cutaneous reaction from perioperative medications, most commonly:

• Antibiotics (cefazolin, cephalosporins) - leading cause of perioperative allergic reactions 1
• Other perioperative drugs administered during anesthesia
• Less likely but possible: acute localized exanthematous pustulosis (ALEP) confined to surgical areas 2

The isolated skin manifestation without systemic symptoms (hypotension, bronchospasm, angioedema) suggests a Grade I reaction on the Ring and Messmer scale 1.

Immediate Management

Clinical Assessment Priority

Determine reaction severity by checking for:

• Systemic involvement: Blood pressure, heart rate, respiratory status
• Extent of rash: Localized vs. generalized, presence of pustules, blistering, or mucosal involvement
• Associated symptoms: Pruritus, angioedema, gastrointestinal symptoms, fever

If Grade I (Isolated Skin Findings)

• No epinephrine required 1
• Antihistamines (H1-blockers) for symptomatic relief
• Document all drugs administered perioperatively
• Photograph the rash for documentation

If Progression or Systemic Signs

• Follow ABCD approach, call for help, 100% oxygen 1
• Epinephrine if hypotension or multi-organ involvement develops 1

Critical Diagnostic Steps

1. Obtain serum tryptase if still within 1-4 hours of reaction onset (compare to baseline sample obtained 24+ hours later) 1
2. Document complete drug list: All antibiotics, anesthetics, neuromuscular blockers, antiseptics (chlorhexidine), dyes used during surgery
3. Rule out differential diagnoses:
   • Non-specific histamine release from opioids (usually immediate, not day 1) 1
   • Exacerbation of underlying chronic urticaria 1
   • DRESS syndrome (typically 2-6 weeks post-exposure, not 1 day) 3

Post-Acute Management

Mandatory allergy investigation before future surgeries 1:

• Refer to allergist/immunologist for skin testing and specific IgE testing
• Testing should occur 4-6 weeks after reaction (allows for refractory period) 1
• Identify specific culprit and cross-reactive drugs

Document in medical record:

• "Suspected perioperative drug allergy - avoid [suspected drug] pending formal allergy testing"
• Alert all healthcare providers to prevent re-exposure 1

Key Pitfalls to Avoid

• Do not dismiss isolated skin reactions - they indicate sensitization and risk more severe reactions with re-exposure
• Do not assume "just a rash" - one-third of patients with documented chlorhexidine allergy were accidentally re-exposed in healthcare settings 1
• Do not proceed with elective surgery without allergy investigation if severe reaction occurred 1
• Elderly patients (74 years) have increased risk of adverse drug reactions and altered pharmacokinetics 4

If Future Surgery Needed

Emergency Surgery

• Use regional/inhalational techniques to minimize IV drug exposure
• Avoid: latex, chlorhexidine, NMBAs, penicillins/cephalosporins if possible 1
• Risk-benefit assessment for each drug choice

Elective Surgery

• Complete allergy investigation first before proceeding 1
• Avoid all exposures given before the reaction occurred
• No evidence that prophylactic antihistamines or corticosteroids prevent true anaphylaxis 1

The facial distribution in this case is notable - while ALEP can localize to surgical sites (locus minoris resistentiae) 2, a hernia surgery would not directly involve the face, making systemic drug distribution more likely than localized phenomenon.