Differential Effects of Low Dose Lidocaine on C-Fiber Classes in Humans

• Published in: The journal of pain Vol. 13; no. 12; pp. 1232 - 1241
• Main Authors: Kankel, Jennifer, Obreja, Otilia, Kleggetveit, Inge Petter, Schmidt, Roland, Jørum, Ellen, Schmelz, Martin, Namer, Barbara
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.12.2012
• Subjects: activity dependent; Adult; Anesthesia & Perioperative Care; Anesthetics, Local - administration & dosage; Clinical Neurophysiology; Female; Human nociceptor; Humans; Klinisk neurofysiologi; lidocaine; Lidocaine - administration & dosage; local anesthetic; Male; microneurography; Nerve Fibers, Unmyelinated - classification; Nerve Fibers, Unmyelinated - drug effects; Nerve Fibers, Unmyelinated - physiology; Pain Medicine; Reaction Time - drug effects; Reaction Time - physiology; Treatment Outcome; Young Adult; activity dependent; local anesthetic; Human nociceptor; microneurography; lidocaine
• ISSN: 1526-5900; 1528-8447; 1528-8447
• DOI: 10.1016/j.jpain.2012.09.008

Abstract The nonselective sodium channel blocker lidocaine is widely used as a local anesthetic but also systemically for treatment of postoperative and neuropathic pain. Voltage-gated sodium channels are crucial for action potential generation and conduction, and their availability controls the amount of activity-dependent conduction velocity slowing. This important axonal property, as assessed by microneurography, is used to differentiate human mechanoinsensitive (silent) nociceptors from the classical polymodal nociceptors. In the current study, microneurography was used to assess axonal properties of the 2 main nociceptor classes in humans, before and after intradermal injection of lidocaine .1% or control saline solution in the receptive field. In mechanosensitive nociceptors, lidocaine reduced baseline conduction velocity and turned activity-dependent slowing into speeding of conduction. In contrast, mechanoinsensitive fibers were not affected in their baseline conduction velocity or their activity-dependent slowing, but probability of conduction block with repetitive stimulation increased. Recovery cycles showed reduced hyperpolarization in all C-fiber classes after lidocaine injections. These results support our hypothesis that sodium channel subtypes are differentially expressed in the 2 nociceptor classes of mechanosensitive C-fibers (CMs) and mechanoinsensitive C-fibers (CMis). Perspective This study reveals that microneurography can be used to assess pharmacological effects on single C-fibers directly in humans.