Article Text

Download PDFPDF
Relative Contribution of Adjuvants to Local Anesthetic for Prolonging the Duration of Peripheral Nerve Blocks in Rats
  1. Asokumar Buvanendran, MD,
  2. Jeffrey S. Kroin, PhD,
  3. Jinyuan Li, MD, PhD,
  4. Mario Moric, MS and
  5. Kenneth J. Tuman, MD
  1. From the Department of Anesthesiology, Rush University Medical Center, Chicago, IL
  1. Address correspondence to: Asokumar Buvanendran, MD, Department of Anesthesiology, Rush University Medical Center, 600 South Paulina, Chicago, IL 60612 (e-mail:


Background and Objectives A chemically compatible, safe 4-drug multimodal formulation of bupivacaine combined with 3 adjuvants (clonidine, buprenorphine, and dexamethasone) has been proposed for long-lasting single-injection peripheral nerve blocks in patients. However, the relative importance of each of the adjuvants of the 4-drug formulation in producing long-lasting nerve blocks has not been determined. The aim of this study in rats was to determine which adjuvants (clonidine, buprenorphine, or dexamethasone) are essential for producing a long-lasting nerve block.

Methods After baseline sensory and motor responses were recorded, 0.1 mL of drug solution was injected into the sciatic notch of rats. Animals were reevaluated at 10-minute intervals after injection for the absence or presence of sensory and motor response in the sciatic nerve. The 4-drug formulation of 0.25% bupivacaine plus all 3 adjuvants (clonidine, buprenorphine, and dexamethasone), 0.25% bupivacaine with 1 or 2 of the adjuvants added separately, and 0.25% bupivacaine alone were compared for duration of nerve block.

Results The 4-drug multimodal solution produced a longer duration of sensory and motor nerve block than 0.25% bupivacaine alone (P < 0.0001). Bupivacaine plus clonidine also produced a longer duration of nerve block than 0.25% bupivacaine alone (P = 0.0157), but bupivacaine plus buprenorphine or bupivacaine plus dexamethasone did not prolong nerve block compared to bupivacaine alone. There was no difference (P = 0.1414) in the duration of nerve block between the 4-drug multimodal solution versus bupivacaine plus clonidine.

Conclusions This animal study confirmed that the 4-drug multimodal formulation proposed for clinical nerve block produces superior duration of action compared to local anesthetic alone. This rat sciatic nerve model also indicated that one of the 3 adjuvants, clonidine, could by itself account for the extended duration of nerve block of bupivacaine.

Statistics from

Request Permissions

If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.


  • The authors declare no conflict of interest.

    This work was supported by University Anesthesiologists, S.C., Chicago, IL.