Analgesic concentrations of lidocaine suppress tonic A-delta and C fiber discharges produced by acute injury.
Intravenous lidocaine has been shown to relieve acute postoperative pain and chronic neuropathic pain. It is not known whether analgesia produced by 2-10 micrograms/ml plasma concentrations of lidocaine is due to an effect on peripheral-pain-transducing nerves or to central nervous system effects. The current study examined effects of analgesic concentrations of lidocaine on injury-induced discharge of A-delta and C fibers, using the in vitro rabbit corneal nerve preparation. Lidocaine at concentrations from 1-20 micrograms/ml reversibly suppressed tonic action potential discharge of acutely injured nerves. The median effective concentration (ED50) (5.7 micrograms/ml) corresponds to clinically effective plasma concentrations for analgesia. Electrically evoked nerve conduction was not blocked until lidocaine concentrations were greater than 250 micrograms/ml. Thus, analgesia produced by lidocaine appears to result from suppression of tonic neural discharge in injured peripheral A-delta and C fiber nociceptors.
Tanelian
D L
DL
Department of Anesthesia, Stanford University School of Medicine, California 94305.
MacIver
M B
MB
D000818:Animals; D003315:Cornea / Q000294:innervation; D065306:Corneal Injuries; D003864:Depression, Chemical; D066298:In Vitro Techniques; D008012:Lidocaine / Q000494:pharmacology*; D009412:Nerve Fibers / Q000187:drug effects / Q000502:physiology*; D009413:Nerve Fibers, Myelinated / Q000187:drug effects / Q000502:physiology*; D011817:Rabbits
D008012:Lidocaine