Coapplication of lidocaine and membrane-impermeable lidocaine derivative QX-222 produces divergent effects on evoked and spontaneous nociceptive behaviors in mice.

The present study was aimed at investigating the analgesic properties of a combination of lidocaine and QX-222 and its effects on evoked pain behavior (complete Freund's adjuvant-induced allodynia and hyperalgesia in inflammatory condition) and spontaneous pain behavior (formalin-induced acute pain) in mice. Drugs were injected adjacent to sciatic nerve or into plantar. Motor function, thermal withdrawal latency, mechanical withdrawal threshold, and licking/biting were evaluated by behavioral tests. A combination of lidocaine and QX-222 adjacent sciatic nerve injection produced the long-lasting sensory-specific nerve block, and intraplantar injection inhibited spontaneous pain in the formalin-treated mice but did not detectably attenuated hyperalgesia and allodynia in the complete Freund's adjuvant- (CFA-) treated mice. Our results suggest that a combination of lidocaine and QX-222 achieves a long-lasting differential block (sensory selective) and produces divergent effects on evoked and spontaneous pain behaviors in mice.