How long does EMLA (Eutectic Mixture of Local Anesthetics) cream take to work?

How Long Does EMLA Cream Take to Work

EMLA cream (Eutectic Mixture of Local Anesthetics) requires 60 minutes to reach full effectiveness on intact skin. 1

Timing of EMLA Effectiveness

• EMLA cream requires a longer application time compared to newer topical anesthetics, with full effectiveness achieved after 60 minutes of application under occlusion 1
• The depth of anesthesia increases with application time:
  • After 60 minutes: Anesthesia to depths of 1-2 mm 2
  • After 120 minutes: Anesthesia to depths of 2-3 mm 2
  • After 3-4 hours: Anesthesia to depths of up to 6 mm 2

Alternative Topical Anesthetics with Faster Onset

• Liposomal 4% lidocaine cream (LMX4) provides anesthesia in approximately 30 minutes 1
• Heat-activated anesthetic systems can work in as little as 10-20 minutes 1
• Lidocaine-epinephrine-tetracaine (LET) combinations for open wounds provide anesthesia in 10-20 minutes 1

Regional Variations in EMLA Effectiveness

• The effectiveness of EMLA varies by anatomical location due to differences in skin thickness and blood flow 3:
  • Face: Faster onset but shorter duration due to higher blood flow
  • Back: Rapid onset but shorter duration after cream removal
  • Extremities (hands, arms): Slower onset but longer duration after removal
  • Thicker skin areas require longer application times 3

Clinical Applications and Considerations

• EMLA is commonly used for:

  • Venipuncture and IV line placement 1
  • Lumbar puncture preparation 1
  • Laceration repair (although not FDA-approved for this purpose) 1
  • Intrauterine device placement 1

• Contraindications include:

  • Allergy to amide anesthetics 1
  • Non-intact skin 1
  • Recent sulfonamide antibiotic use 1
  • Congenital or idiopathic methemoglobinemia 1

• For patients under 12 months or weighing less than 10 kg, the dose should be reduced 1

Practical Application Tips

• Apply EMLA cream to at least two potential venipuncture sites when preparing for IV placement 1
• Cover the application with an occlusive dressing to enhance penetration 2
• For procedures that cannot be delayed, consider alternative methods such as intradermal lidocaine injection 1
• For needle insertion procedures (like totally implantable venous access devices), even 30 minutes of application provides significant pain reduction compared to no anesthetic, though 60 minutes is more effective 4

Common Pitfalls

• Inadequate application time is the most common reason for ineffective anesthesia with EMLA 2
• Failure to apply occlusion can reduce effectiveness 2
• Topical anesthetics like EMLA do not provide complete pain relief for all procedures 1
• Standard topical anesthetics like EMLA may not be effective for pain reduction during photodynamic therapy 1