Medication Allergies

Overview:

• Allergic reactions to medications involve the immune system and differ from non-allergic (idiosyncratic or toxic) adverse effects.

• Commonly involved drugs in orthopaedics include antibiotics (especially beta-lactams), NSAIDs, and anaesthetic agents.

Classification of Drug Reactions:

• Type I (Immediate): IgE-mediated (e.g., anaphylaxis, urticaria)

• Type II: Cytotoxic (e.g., hemolytic anaemia)

• Type III: Immune complex (e.g., serum sickness)

• Type IV (Delayed): T-cell mediated (e.g., contact dermatitis, Stevens-Johnson Syndrome)

Common Culprit Medications in Orthopaedics:

• Penicillins/Cephalosporins → rash, anaphylaxis

• NSAIDs → urticaria, bronchospasm, angioedema

• Local anaesthetics → contact dermatitis (rarely true allergy)

• Opioids → pseudoallergic histamine release (not true IgE)

Clinical Features:

• Rash, pruritus, urticaria

• Facial swelling, wheezing, hypotension

• Joint symptoms (serum sickness-like reaction)

• Fever, eosinophilia (DRESS syndrome)

Diagnosis:

• Detailed drug history

• Skin prick and intradermal testing (limited to certain drugs)

• Serum tryptase (in anaphylaxis)

• Drug challenge in specialist settings

Management:

• Avoidance of suspected drug

• Use alternatives (e.g., clindamycin or vancomycin for penicillin allergy)

• Premedication for mild allergy history (e.g., antihistamines, steroids)

• Intraoperative alert and documentation essential

• Desensitisation in selected cases

Orthopaedic Considerations:

• Preoperative assessment is critical

• Use of allergen-free cement components, prophylactic antibiotics, or analgesics

• Always update electronic health records and warn the surgical team