The effect of intravenous lidocaine, tocainide, and mexiletine on spontaneously active fibers originating in rat sciatic neuromas.

The effects of intravenously administered subanesthetic concentrations of lidocaine, tocainide, and mexiletine on spontaneously active fibers (SAFs) originating in 7-day-old rat sciatic neuromas were studied. Control injections of normal saline caused no decrease in SAF or discharge rate. Lidocaine and tocainide given in incremental doses of 5, 10, 15, 20 and up to 25 mg/kg caused nearly all observed SAFs to stop firing. Mexiletine given in doses of 3, 5, 7, 10 and up to 15 mg/kg showed similar results at lower doses. All agents decreased the sensitivity of SAF to mechanical stimulation. No conduction blockade occurred at these doses of intravenously administered local anesthetics. The demonstrated reduction in firing rate of SAF may explain the pain relief observed in clinical trials of these orally available agents.