What are the considerations for mixing bupivacaine with lidocaine for local anesthesia?

Mixing Bupivacaine with Lidocaine for Local Anesthesia

Mixing bupivacaine with lidocaine for local anesthesia is safe and effective, but offers no proven clinical advantage over using either agent alone in terms of onset time or duration of anesthesia. 1

Safety and Efficacy

• Mixing local anesthetics such as bupivacaine and lidocaine is a common practice that has been studied in multiple randomized controlled trials in both ophthalmologic and dermatologic settings 1
• Evidence suggests that mixing these agents for local infiltration and nerve blocks is safe and effective 1
• The FDA drug label does not recommend mixing bupivacaine with other local anesthetics due to insufficient data on clinical use of such mixtures 2

Clinical Benefits and Limitations

• Theoretical Benefits:

  • The traditional rationale for mixing these agents is to combine lidocaine's rapid onset with bupivacaine's longer duration 3
  • However, research does not support this theoretical advantage 3, 4

• Onset Time:

  • No significant difference in onset times has been demonstrated between bupivacaine alone, lidocaine alone, or mixtures of the two 3, 4
  • In one study, mean onset times ranged from 12-29 seconds across all tested solutions without statistical significance 3

• Duration of Action:

  • Research shows that mixing lidocaine with bupivacaine actually reduces the duration of anesthesia compared to using bupivacaine alone 5, 6
  • One study found no significant difference between the duration of plain lidocaine and a 50/50 mixture, while bupivacaine alone had a prolonged duration compared to both 4

Important Considerations

• Sequential Administration:

  • Injecting bupivacaine into an area previously injected with lidocaine (even after a 1-hour interval) reduces the extended duration of bupivacaine 5
  • This suggests that using bupivacaine as a post-surgical block in the presence of residual lidocaine is not advantageous 5

• Buffering Considerations:

  • Sodium bicarbonate can be added to lidocaine to reduce injection pain, but should not be added to bupivacaine as it may cause precipitation of the anesthetic and decrease efficacy 7, 1

• Epinephrine Addition:

  • Adding epinephrine to either agent or their mixture is safe (including in digits) and can prolong anesthetic duration by approximately 200% 1, 8
  • Use the lowest effective concentration of epinephrine (typically 1:100,000 or 1:200,000) 1, 8

Pharmacokinetic Considerations

• Plasma concentrations of bupivacaine are higher and remain elevated longer when used alone compared to when mixed with lidocaine 6
• While this suggests a potential safety benefit of mixtures (lower peak plasma levels of each drug), this may be offset by the presence of significant plasma concentrations of both drugs 6

Clinical Decision Making

• The decision to use a mixture versus a single agent should be based on the clinician's experience and comfort level 1
• For procedures requiring rapid onset and extended duration, consider:
  • Using bupivacaine alone for both rapid onset (clinically acceptable) and extended duration 5, 9
  • Using lidocaine with epinephrine for rapid onset and moderate duration 8
  • Avoiding sequential administration of the two agents 5

Pitfalls to Avoid

• Do not buffer bupivacaine with sodium bicarbonate as it may precipitate and reduce efficacy 1, 7
• Do not expect faster onset or longer duration from mixing the two agents compared to using them individually 3, 4, 5
• Avoid using mixtures when maximum duration is the primary goal, as bupivacaine alone provides longer duration 4, 5