What is the recommended method for calculating the maximum dose of lidocaine (local anesthetic) and Marcaine (bupivacaine) when used together in the same case?

Calculating Maximum Dose of Lidocaine and Bupivacaine (Marcaine) When Used Together

When using lidocaine and bupivacaine (Marcaine) together in the same case, calculate the fraction of maximum dose used for each drug separately and ensure their sum does not exceed 1 (or 100%).

Understanding Maximum Doses

The maximum safe doses for each agent when used alone are:

Agent	Without Epinephrine	With Epinephrine
Lidocaine	4.5 mg/kg	7.0 mg/kg
Bupivacaine (Marcaine)	2.5 mg/kg	3.0 mg/kg

These limits are established in multiple guidelines, including those from the American Academy of Dermatology 1 and FDA drug labeling 2, 3.

Calculation Method

When using both agents together, follow this approach:

1. Calculate the fraction of maximum dose for each drug:

   • Lidocaine fraction = (actual dose used ÷ maximum dose)
   • Bupivacaine fraction = (actual dose used ÷ maximum dose)

2. Add these fractions together:

   • Total fraction = Lidocaine fraction + Bupivacaine fraction

3. Ensure the total fraction does not exceed 1 (100%)

Example Calculation

For a 70 kg adult using both drugs with epinephrine:

• Maximum lidocaine dose: 7.0 mg/kg × 70 kg = 490 mg
• Maximum bupivacaine dose: 3.0 mg/kg × 70 kg = 210 mg

If you use 245 mg lidocaine (50% of max) and 105 mg bupivacaine (50% of max):

• Lidocaine fraction: 245 ÷ 490 = 0.5 (50%)
• Bupivacaine fraction: 105 ÷ 210 = 0.5 (50%)
• Total: 0.5 + 0.5 = 1.0 (100% of combined maximum)

Important Considerations

• Special Populations: Reduce doses by 30% in infants younger than 6 months 4
• Anatomical Location: Use lower doses in highly vascular areas 1, 4
• Safety Precautions:
  • Calculate maximum doses before administration 4
  • Monitor for early signs of toxicity (circumoral numbness, facial tingling, slurred speech) 4
  • Have resuscitation equipment and 20% lipid emulsion available 4
  • Aspirate before injection to avoid intravascular administration 4

Practical Tips

• Use the lowest effective concentration and dose to minimize toxicity risk 2
• Consider the specific procedure and anatomical location when determining doses
• Remember that epinephrine increases the maximum allowable dose but doesn't eliminate toxicity risk
• For multistage procedures like Mohs surgery, a maximum of 500 mg lidocaine delivered over several hours is recommended 1

This fractional approach ensures you stay within safe limits while allowing you to benefit from the different onset times and durations of action of these two local anesthetics.