Sevoflurane suppresses behavioral response in the rat formalin test: combination with intrathecal lidocaine produced profound suppression of the response.

We investigated the effects of intrathecal (i.t.) lidocaine, inhalation sevoflurane, and a combination of i.t. lidocaine and sevoflurane on the formalin test in rats. Group 1 (control) received i.t. saline 10 microl. Groups 2 and 3 received i.t. lidocaine 200 microg and 400 microg, respectively. Groups 4-6 received 1.2%, 2.4% and 3.6% sevoflurane, respectively. Interaction of drugs was analyzed using a dose addition model. Group 7 received i.t. lidocaine 200 microg and 1.2% sevoflurane. The biphasic behavioral activity of the hindpaw of rats was observed. This study showed that i.t. lidocaine or inhalation sevoflurane before formalin injection, significantly suppressed the behavioral activity of the hindpaw of rats, and that this suppression was significantly potentiated by the co-administration of i.t. lidocaine and inhalation sevoflurane.