A comparative evaluation of the effects of local anesthetics combined with morphine and administered epidurally

: The authors compare the efficacies of trimecaine (8 mg/kg), lidocaine (8 mg/kg), azacaine (2 and 3 mg/kg) alone and in combination with morphine (1.2 mg/kg), administered epidurally. Analgesia efficacy and duration were assessed by the electrostimulation method in experimental rabbits. First the pain threshold was defined, then the tested drugs were injected epidurally; the degree of the pain threshold rise permitted a judgment on the analgetic effect of the drugs. Combined injection of morphine and any of the tested anesthetics to the epidural space considerably prolonged the analgesia. The duration of the analgetic effect was the longest (over 24 h) with azacaine-based mixtures. Preliminary injection of morphine (1 h before azacaine) was conducive to a more rapid development of the epidural block and a more smooth course of analgesia. Experiments with mice have shown that addition of morphine to azacaine in the before volumes did not change azacaine toxicity.