We describe a mouse model for evaluation of skill anesthesia after infiltra
tion of local anesthetic. The method involves subcutaneous injection of the
anesthetic over the abdomen, and monitoring the vocalization response to e
lectrical stimulus as a measure of analgesia. Prior to drug injection, the
vocalization threshold was determined. Mice that vocalized at less than or
equal to 8 mA were included in the study. The model was tested using repres
entative agents of the two classes of local anesthetics, bupivacaine, an am
ide, and chloroprocaine, an ester. The time course and dose response were a
ssessed after injection. The median analgesic time was 15, 40, and 55 min f
or 0.015%, 0.0625%, and 0.25% bupivacaine and 30, 50, and 55 min for 0.125%
, 0.25%, and 2.0% chloroprocaine, respectively. Statistical analysis of the
data showed that this method is sufficiently sensitive to detect differenc
es between the dose and duration of local anesthesia (p < 0.05, by log rank
test of the survival curves). To further validate the model, we compared t
he duration of anesthesia between the 0.5% bupivacaine and a new long - act
ing liposomal formulation of 2% bupivacaine. The results showed that the ne
w formulation significantly prolonged the duration of anesthesia (p < 0.05)
. This simple and reliable method may facilitate research on the pharmacolo
gy of infiltration anesthesia and the development of new local anesthetics
and/or formulations. (C) 2000 Elsevier Science Inc. All rights reserved.