Is chronic ethanol consumption associated with tolerance to intrathecal lidocaine in the rat?

Intoxication with alcohols can produce anesthesia. In contrast, chronic ethanol consumption can produce tolerance to inhaled and other general anesthetics. We tested whether ongoing consumption decreased, and whether withdrawal from such consumption increased, the intrathecal dose of lidocaine that induces sensory and motor blockade in female Sprague-Dawley rats. Sensory blockade was assessed using the tail-flick test, and motor blockade by the animal's inability to move its hind limbs. Rats were tested before commencing ethanol intake; during ethanol ingestion (9 days after beginning ingestion); and on the 15th day of ingestion, 14 h after withdrawing ethanol from their diet. Pair-fed control rats were tested at the same intervals. Ongoing administration of ethanol decreased the dose of lidocaine required to produce sensory blockade, but this difference was not significant relative to the control group (i.e., the difference was significant within group but not across groups). Withdrawal of ethanol increased the dose requirements for sensory and motor blockade by 80% and 53% (P less than 0.01 and P less than 0.0001) and decreased the duration of the motor blockade (P less than 0.01). Dose requirements producing sensory block differed between alcoholic and control groups (P less than 0.0001). These results suggest that chronic ethanol intake produces tolerance to the local anesthetic effects of lidocaine. Whether this change results from a change in kinetics or in sensitivity is not known, but the latter would seem more likely, because duration of blockade was minimally affected or unaffected.