Intrathecal acetylsalicylic acid and indomethacin are not analgesic for a supramaximal stimulus.

Intrathecal acetylsalicylic acid and indomethacin are analgesic for painful stimuli, and this has been demonstrated when the noxious stimuli are applied to normal and inflamed tissue. This study determined whether these drugs would alter the response to a supramaximal stimulus, e.g., tail-clamp. Rabbits were anesthetized with halothane and after arterial and venous cannulation, an intrathecal catheter was placed via a lumbar laminectomy. The minimum alveolar anesthetic concentration was then determined. Groups 1 (n = 8) and 2 (n = 6) received 0.5 mg/kg acetylsalicylic acid intrathecally and Group 3 (n = 7) 0.5 mg/kg indomethacin intrathecally. Group 4 (n = 8) did not undergo a laminectomy and received acetylsalicylic acid 25 mg/kg intraperitoneally. In addition, in Groups 2-4, before the surgical procedures, carrageenin 1 mg was injected into the tail to evoke an inflammatory response. Approximately 20 min after injection of the study drugs, minimum alveolar anesthetic concentration was determined again. In Groups 1-4, control minimum alveolar anesthetic concentration was 1.2 +/- 0.2%, 1.4 +/- 0.3%, 1.2 +/- 0.2%, and 1.5 +/- 0.1%, respectively; there was no statistically significant change in any group after injection of the study drugs. There were no temperature, hematocrit, or arterial blood pressure differences between groups or after injection of the study drugs. In this model intrathecal acetylsalicylic acid and indomethacin do not provide analgesia for a supramaximal stimulus.