The effects of mexiletine on excitability properties of human median motor axons

详细信息    查看全文

• 作者：Kuwabara ; Satoshi ; Misawa ; Sonoko ; Tamura ; Noriko ; Kanai ; Kazuaki ; Hiraga ; Akiyuki ; Ogawara ; Kazue ; et. al.
• 关键词：Mexiletine ; Sodium channel ; Persistent sodium channel ; Neuropathy ; Axonal excitability ; Threshold tracking
• 刊名：Clinical Neurophysiology
• 出版年：2005
• 出版时间：February, 2005
• 年：2005
• 卷：116
• 期：2
• 页码：284-289
• 全文大小：134 K

文摘

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.

Significance

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.