• Alimorad G Djalali, Jeffrey Chi-Fei Wang, Jose Ramon Perez-Valdivieso, Thomas Danninger, Gerhard Fritsch, David Zurakowski, and Peter Gerner.
• Department of Anesthesia, Stanford University School of Medicine, 300 Pasteur Dr., Room H3687, MC 5640, Stanford, CA 94305, USA. adjalali@stanford.ed
• Anesth. Analg.. 2013 Apr 1;116(4):944-8.

BackgroundEphedrine is a direct/indirect vasoactive drug. In addition, it also possesses intrinsic local anesthetic properties, mainly due to its sodium-channel blockage. We investigated whether ephedrine demonstrates a synergistic effect with bupivacaine and lidocaine when injected via a spinal catheter into the spinal space of rats.MethodsSpinal catheters were surgically placed in 47 rats (n = 8 per group; 7 rats were excluded.) Bupivacaine, lidocaine, and ephedrine in various concentrations and constant volumes (60 μL) were injected into the spinal catheters to determine the equipotency of each drug. Ephedrine in combination with either bupivacaine or lidocaine was then injected into the spinal catheters.ResultsEphedrine demonstrated statistically significant synergistic effects with bupivacaine as well as with lidocaine in fixed combinations. The combination index reflecting a synergistic effect was 0.792 (95% confidence interval: 0.665-0.919) for ephedrine + bupivacaine and 0.663 (95% confidence interval: 0.532-0.794) for ephedrine + lidocaine.ConclusionEphedrine combined with either bupivacaine or lidocaine acted synergistically to block motor function and has the potential to reduce the amount of local anesthetic needed for spinal block. The synergistic effect of ephedrine in combination with local anesthetics is an interesting pharmacological phenomenon that warrants further clinical evaluation.

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