title: The effects of mexiletine on excitability properties of human median motor axons.
abstract: OBJECTIVE
  To investigate the effects of mexiletine, an analog of lidocaine, on excitability of human axons in vivo.
  
  
  METHODS
  Threshold tracking was used to measure multiple excitability indices (strength-duration time constant, rheobase, refractoriness, supernormality, and threshold electrotonus) in median motor axons of 20 patients with neuropathic pain or muscle cramping, before and 3 months after treatment with oral 300 mg mexiletine per day.
  
  
  RESULTS
  After treatment, there was a reduction in pain/muscle cramps, associated with decreased strength-duration time constants (P=0.01), increased rheobasic currents (P=0.06), and lower refractoriness (P=0.02), all of which were consistent with reduced nodal Na+ currents. Supernormality and threshold electrotonus did not change significantly. The changes in strength-duration properties suggest a decrease in persistent Na+ conductance. The lowered refractoriness after treatment might result from reduced transient Na+ currents, but the lack of change in supernormality and threshold electrotonus was not consistent with this hypothesis.
  
  
  CONCLUSIONS
  Oral mexiletine in a dosage of 300 mg daily suppresses persistent Na+ currents in human motor axons.
  
  
  CONCLUSIONS
  Measurements of the excitability indices can be used for non-invasive assessment and monitoring of the effects of mexiletine in patients with neuropathic pain or muscle cramps.
authors.affiliation: Department of Neurology, Chiba University School of Medicine, 1-8-1 Inohana, Chuo-ku, Chiba 260-8670, Japan. kuwabara-s@faculty.chiba-u.jp
authors.forename: Satoshi
authors.initials: S
authors.lastname: Kuwabara
authors.forename: Sonoko
authors.initials: S
authors.lastname: Misawa
authors.forename: Noriko
authors.initials: N
authors.lastname: Tamura
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Kanai
authors.forename: Akiyuki
authors.initials: A
authors.lastname: Hiraga
authors.forename: Kazue
authors.initials: K
authors.lastname: Ogawara
authors.forename: Miho
authors.initials: M
authors.lastname: Nakata
authors.forename: Takamichi
authors.initials: T
authors.lastname: Hattori
mesh_terms: D000200:Action Potentials; D000284:Administration, Oral; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000779:Anesthetics, Local / Q000008:administration & dosage / Q000627:therapeutic use*; D001369:Axons / Q000187:drug effects*; D004056:Differential Threshold; D004334:Drug Administration Schedule; D004553:Electric Conductivity; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000503:physiopathology; D008801:Mexiletine / Q000008:administration & dosage / Q000627:therapeutic use*; D008875:Middle Aged; D009046:Motor Neurons / Q000187:drug effects*; D009120:Muscle Cramp / Q000188:drug therapy / Q000503:physiopathology*; D009437:Neuralgia / Q000188:drug therapy / Q000503:physiopathology*; D012032:Refractory Period, Electrophysiological; D026941:Sodium Channel Blockers / Q000008:administration & dosage / Q000627:therapeutic use*; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism
chemical_list: D000779:Anesthetics, Local; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D008801:Mexiletine