Local Anaesthetic Hypersensitivity

Local anaesthetic hypersensitivity is a reaction to local anaesthetic drugs. Most reported reactions are not allergic, and true allergy is rare, with fewer than 1% of cases confirmed.

Pathophysiology. Local anaesthetics are esters (procaine, benzocaine, tetracaine, chloroprocaine) or amides (lidocaine, bupivacaine, mepivacaine, ropivacaine, prilocaine, articaine). Esters are metabolised to para aminobenzoic acid and cause more allergy. Amides rarely cause true allergy.

Most symptoms come from anxiety, vasovagal reactions, adrenaline in the preparation (palpitations, tremor), systemic toxicity, or preservatives (methylparaben, sulphites). Delayed contact dermatitis (type IV) occurs with topical use.

Cross-reactivity occurs within the ester group and not between esters and amides. Cross-reactivity within amides is uncommon.

• Immediate IgE-mediated allergy: urticaria, angio oedema, wheeze, hypotension within minutes (rare)
• Delayed local eczematous reaction at the injection or application site (type IV)
• Anxiety and vasovagal reaction: pallor, sweating, dizziness, bradycardia, fainting
• Adrenaline effects: tachycardia, tremor, anxiety, headache
• Toxicity: perioral numbness, tinnitus, metallic taste, confusion, seizures, arrhythmia
• Reactions with preservatives or sulphite containing preparations

• History: drug, route, dose, time to onset, features, and whether adrenaline or a preservative was in the preparation.
• Skin prick and intradermal tests with preservative free local anaesthetics (lidocaine 1%, bupivacaine 0.25%, mepivacaine and an alternative), with a positive and negative control.
• Subcutaneous graded challenge if skin tests are negative: lidocaine 1% (10 mg/mL) subcutaneously, 0.1 mL, then 0.5 mL, 1 mL and 2 mL at 20 to 30 minute intervals up to the dose planned for the procedure, with observation for 1 hour afterwards.
• Patch testing for delayed reactions.
• Serum tryptase if an immediate reaction occurred.

Differential diagnosis.

• Vasovagal reaction and anxiety
• Adrenaline reaction
• Local anaesthetic systemic toxicity
• Reaction to latex, chlorhexidine, antibiotics or other perioperative agents
• Methylparaben or sulphite sensitivity
• Allergic contact dermatitis from topical anaesthetic or preservative

• Remove the label when tests and challenge are negative, and record the result in the notes.
• Confirmed allergy: avoid the drug and related agents of the same class. Use an agent from the other class after a negative test and challenge (for example an amide, if allergic to an ester).
• Maximum doses: lidocaine 4.5 mg/kg (maximum 300 mg) without adrenaline, and 7 mg/kg (maximum 500 mg) with adrenaline, and lower in hepatic impairment.
• Anaphylaxis: adrenaline 0.5 mg intramuscularly (children 0.01 mg/kg, maximum 0.5 mg) into the anterolateral thigh, repeated after 5 minutes if no improvement, plus oxygen and intravenous fluids, and observation for at least 6 hours.
• Local anaesthetic systemic toxicity: stop the injection, give airway support and benzodiazepines for seizures, and lipid emulsion 20%, 1.5 mL/kg intravenous bolus, followed by an infusion of 15 mL/kg/hour.
• Delayed contact dermatitis: avoid the topical agent and use an alternative class or preservative free form.
• Alternatives when no local anaesthetic is possible: diphenhydramine 1% infiltration (dental or minor surgery), general anaesthesia or sedation.

Special groups.

• Dental patients: most reactions are vasovagal, and a supervised test with the planned agent allows treatment.
• Patients with ester allergy: topical benzocaine and related products contain para aminobenzoic acid derivatives and are also avoided.

Monitoring. Observe for at least 1 hour after challenge. Update the allergy record.

Referral and escalation. Refer to allergy for any suspected local anaesthetic reaction when future procedures are needed. Emergency for anaphylaxis or seizures.