Local Anaesthetic Properties vs. Neurotoxicity for (+)- and (−)-Carvone: An Ex Vivo Electrophysiological Study

Abstract

! The two carvone enantiomers were tested for local anaesthetic activity at concentrations of 10 and 20 mM using a nerve preparation based on the isolated sciatic nerve of the frog and were found to induce similar responses. They eliminated the evoked compound action potential within 6-7 min, while there was an instant 83 to 87% recovery when they were washed out from the nerve preparation and replaced with normal saline. Both car-vones have the same pattern of action as 10 mM lidocaine, the standard local anaesthetic, but they are 3-4 times less active with respect to the time of response. When the nerves were exposed to the carvones for a period of time longer than 6-7 min, for example 1 h, there was no recovery at all of the evoked compound action potential, indicating a neurotoxic action. In contrast, when nerves were exposed under the same conditions to lidocaine and another natural compound with local anaesthetic properties, 2-heptanone, there was an 80-100% recovery. This unusual neuro-toxic effect of (+)-and (−)-carvone can be a disadvantage for their use in clinical practice.