How can a 1g dose of EMLA (lidocaine and prilocaine) cream be appropriate for a 5kg, 3-month-old patient when the recommended dose is 4.5mg/kg of lidocaine?

Understanding EMLA Dosing in Infants Under 3 Months

The apparent discrepancy is resolved by understanding that EMLA contains both lidocaine AND prilocaine in equal concentrations (2.5% each), so 1 gram of EMLA cream contains only 25mg of lidocaine (not 1000mg), which equals 5mg/kg for a 5kg infant—well within the safe 4.5mg/kg guideline. 1

Breaking Down the Math

The confusion stems from misunderstanding what "1 gram" refers to:

• 1 gram of EMLA cream contains 25mg lidocaine + 25mg prilocaine (2.5% concentration of each) 1
• For a 5kg infant: 25mg ÷ 5kg = 5mg/kg of lidocaine
• This is actually very close to the recommended maximum of 4.5mg/kg for systemic lidocaine dosing

The FDA-approved maximum dose for infants 0-3 months or <5kg is specifically 1 gram of EMLA cream applied to 10cm² for 1 hour maximum. 1

Critical Age-Based Dosing Guidelines

For Infants Under 3 Months (<5kg):

• Maximum total dose: 1 gram of EMLA cream 1
• Maximum application area: 10 cm² 1
• Maximum application time: 1 hour 1
• This translates to approximately 0.5g per application site if using two sites 2

For Infants 3-12 Months (>5kg):

• Maximum total dose: 2 grams of EMLA cream 1
• Maximum application area: 20 cm² 1
• Maximum application time: 4 hours 1

Why the Strict Limitations in Young Infants

The primary concern is methemoglobinemia from prilocaine, not lidocaine toxicity. 2, 3

Key Risk Factors for Toxicity:

• Age <3 months (immature enzyme systems for metabolizing prilocaine) 1, 4
• Concomitant methemoglobin-inducing agents (sulfonamide antibiotics like trimethoprim-sulfamethoxazole) 2, 3
• Excessive application amounts (>1g in infants <3 months) 4, 5
• Prolonged application time (>1 hour in young infants) 4
• Diseased or inflamed skin (eczema, abraded skin increases absorption) 4, 5

Evidence on Safety When Properly Dosed

Clinical trials demonstrate that 1g EMLA applied for 60 minutes in term neonates produces methemoglobin levels of 1.17% (range 0.50-2.53%), well below the 5% threshold requiring intervention. 6

• Meta-analysis of 11 studies showed no significant difference in methemoglobin concentrations between EMLA-treated and placebo-treated neonates when proper dosing was followed 7
• All 12 clinical trials following manufacturer guidelines reported clinically insignificant plasma levels of lidocaine, prilocaine, and metabolites 4

Critical Contraindications

EMLA is absolutely contraindicated in: 2, 3, 1

• Infants <12 months receiving methemoglobin-inducing agents (sulfonamides)
• Congenital or idiopathic methemoglobinemia
• Allergy to amide anesthetics
• Non-intact skin (wounds, mucous membranes require different formulations)
• Premature infants with gestational age <37 weeks 1

Common Pitfalls to Avoid

The most dangerous error is applying adult or older pediatric dosing to young infants. 4, 5

• One case report documented seizures and 20.1% methemoglobin after 30g EMLA application in a child with eczema 5
• Never exceed 1g total dose in infants <3 months, regardless of the number of application sites 1
• Do not apply for longer than 1 hour in this age group, even if anesthesia seems inadequate 1
• Caregivers must be explicitly instructed on proper amounts to prevent accidental overdose 1

Practical Application Protocol

For a 5kg, 3-month-old infant requiring IV access: 2, 1

1. Apply 0.5g EMLA to each of two potential IV sites (total 1g maximum)
2. Cover with occlusive dressing
3. Wait exactly 60 minutes (EMLA requires full hour for effectiveness)
4. Remove cream and proceed with procedure
5. Monitor for pallor, edema at application sites (transient and expected) 6

If the procedure cannot wait 60 minutes, consider liposomal 4% lidocaine (LMX4) which provides anesthesia in 30 minutes, though this has less safety data in neonates. 2