What is topical LET (Lidocaine, Epinephrine, Tetracaine)?

Topical LET: A Combination Anesthetic for Wound Management

Topical LET (Lidocaine, Epinephrine, and Tetracaine) is a compounded liquid or gel preparation that provides excellent wound anesthesia in 10-20 minutes when applied to open wounds, particularly for laceration repair. 1

Composition and Mechanism

• Components:

  • Lidocaine: Amide local anesthetic that blocks sodium channels
  • Epinephrine: Vasoconstrictor that prolongs anesthetic effect
  • Tetracaine: Potent local anesthetic

• Formulation: Can be prepared by in-hospital pharmacies as either:

  • Liquid solution
  • Gel preparation (often preferred for better wound adherence)

Clinical Applications

LET is primarily used for:

• Simple lacerations requiring repair
• Complex or deeper lacerations that may need supplemental anesthesia
• Particularly effective for facial and scalp lacerations in children

Advantages

• Provides excellent wound anesthesia without needle injection
• Onset of action in 10-20 minutes
• Produces visible blanching of wound edges when effective
• More cost-effective than older TAC (Tetracaine, Adrenaline, Cocaine) formulations 2
• Lower systemic absorption compared to other topical anesthetics 3
• Can reduce the pain of subsequent infiltrative anesthesia if needed

Administration Guidelines

1. Dosing:

   • Children >17 kg: 3 mL maximum
   • Children <17 kg: 0.175 mL/kg (based on maximum lidocaine dose of 5 mg/kg) 1

2. Application methods:

   • Place directly on open wound and cover with occlusive dressing, OR
   • Apply using cotton ball soaked with LET solution placed into wound

3. Duration:

   • Allow 10-20 minutes of contact time
   • Effective anesthesia is indicated when wound edges appear blanched

Contraindications

• Allergy to amide anesthetics
• Grossly contaminated wounds 1
• Mucous membrane application (should be avoided)

Comparative Efficacy

• LET has been shown to be more effective than EMLA cream for producing anesthesia to needlestick in lacerations (73% vs 40%) 4
• LET has lower systemic absorption of lidocaine (0.13 μg/mL) compared to other topical anesthetics like Topicaine (0.438 μg/mL) and EMLA (0.72 μg/mL) 3
• LET has replaced older TAC formulations due to better safety profile, lower cost, and comparable efficacy 2

Safety Considerations

• Avoid application to mucous membranes
• Avoid ingestion
• Use appropriate dosing based on patient weight
• Monitor for signs of lidocaine toxicity (though systemic absorption is minimal)

Clinical Pearls

• Protocols for topical anesthetic placement should be developed at triage for laceration repair 1
• LET can be used before subsequent infiltrative anesthesia to reduce injection pain
• The visible blanching effect helps clinicians determine when adequate anesthesia has been achieved
• LET is part of a comprehensive approach to minimizing pain and anxiety during laceration repair

LET represents an important advance in topical anesthesia for wound management, particularly for pediatric patients, by providing effective anesthesia without the pain and anxiety associated with needle injections.