Systemic lidocaine for neuropathic pain relief.

The effectiveness of systemic lidocaine in relieving acute and chronic pain has been recognized for over 35 years. In particular, systemic lidocaine has been utilized both as a diagnostic and therapeutic tool for intractable neuropathic pain during the last decade. The introduction of oral lidocaine congeners such as mexiletine has significantly extended the usage of lidocaine therapy in chronic pain settings. However, a number of clinical issues remain to be addressed including (1) an effective, meaningful dose range for the clinical lidocaine test, (2) the predictive value of the lidocaine test for an oral trial of lidocaine congeners, (3) identification of pain symptoms and signs relieved by systemic lidocaine, (4) comparisons of therapeutic effects between systemic lidocaine and its oral congeners, and (5) long-term outcomes of systemic lidocaine and its oral congeners. Mechanisms of neuropathic pain relief from lidocaine therapy are yet to be understood. Both central and peripheral mechanisms have been postulated. Systemic lidocaine is thought to have its suppressive effects on spontaneous ectopic discharges of the injured nerve without blocking normal nerve conduction. However, there remain inconsistencies in the scientific basis underlying the clinical application of lidocaine therapy. Recent demonstration of changes in tetrodotoxin (TTX)-sensitive and TTX-resistant sodium channels following nerve injury and their link to certain neuropathic pain symptoms may lead to the development of subtype-specific sodium channel blockers. The thoughtful use of lidocaine therapy and the potential application of subtype-specific sodium channel blockers could provide better management of distinctive neuropathic pain symptoms.