Regional cutaneous differences in the duration of bupivacaine local anesthesia in mice

At this time little is know about local anesthesia of the skin, and the sensitivity of different cutaneous regions to local anesthetics. Studies were conducted in mice to test the hypothesis that cutaneous regions are differentially sensitive to bupivacaine, and to the ability of epinephrine (EPI) to prolong local anesthesia. Infiltration of 0.25% and 0.5% bupivacaine s.c. in the dorsal aspect of the mouse tail produced local anesthesia that lasted 15 and 45 min, respectively, against radiant heat nociception. EPI (1:200,000) prolonged the local anesthetic effects of the 0.25% concentration by 45 min, whereas the effect of the 0.5% concentration was extended by only 15 min. Bupivacaine (0.25% and 0.5%) infiltrated in the dorsal aspect of the hind-paw produced local anesthesia that lasted 5 and 30 min, respectively. EPI prolonged the local anesthetic effects of the 0.25% concentration by only 10 min, whereas EPI did not prolong anesthesia but appeared to increase the efficacy of the 0.5% concentration. These results provide evidence of regional differences in cutaneous sensitivity to local anesthetics, and the ability of EPI to extend the duration of anesthesia.