COCAINE AND LIDOCAINE IN COMBINATION ARE SYNERGISTIC CONVULSANTS

The abuse of cocaine has dramatically increased in the recent decade. Cocaine obtained on the illegal market is rarely found in pure form. M ost often it is adulterated with various substances, especially other local anesthetics. Lidocaine is one of the most common local anestheti cs employed for adulteration of illicit cocaine. Toxicity due to the s imultaneous ingestion of cocaine and lidocaine has been reported. Acut e toxicity to cocaine and other local anesthetics is manifested in cen tral nervous system aberrations, such as seizures and convulsions. Thi s study investigated the convulsant potency of cocaine and lidocaine a lone and in combination. Rats were administered intravenous injections of 5 mg/kg or 20 mg/kg of cocaine or lidocaine alone and in combinati on in equal proportion. Seizure activity and intensity were evaluated. The plasma concentration and brain content of each agent was also det ermined at the time of toxicity. The administration of 5 mg/kg of each drug alone did not yield seizure activity. However, the concomitant a dministration of 5 mg/kg of both cocaine and lidocaine produced a seiz ure response nearly equal to that produced after administration of 20 mg/kg of cocaine alone. Diazepam pre-treatment successfully antagonize d the seizures induced by cocaine and lidocaine and raised the seizure threshold dose for the combination treatment by approximately four fo ld. The results suggest that cocaine and lidocaine interact synergisti cally to increase seizure activity and that the nature of this respons e occurs in part through a depression of inhibitory neuronal transmiss ion.