The use of eutectic mixture of lidocaine and prilocaine in mice (Mus musculus) for tail vein injections.

OBJECTIVE: To investigate a topical local anesthesia technique as a means to prevent and/or diminish pain in mice in a laboratory setting associated with tail vein injections performed by personnel in training.

STUDY DESIGN: Prospective, randomized experimental trial.

ANIMALS: Thirty six adult female, 23-28 g CD-1 mice from an in-house training colony. They were acclimated to routine training and handling classes.

METHODS: Eutectic mixture of local anesthetics (EMLA) cream (2.5% lidocaine/2.5% prilocaine) or a bland ointment control (n = 18) was applied on the tail prior to intravenous injection. The injections were performed by novices, who had never attempted the procedure, and experienced personnel. All participants were blinded to treatment groups. Three injection attempts were allowed per animal. The mice were observed and scored by blinded evaluators for behavioral and physiological changes, including respiratory rate, vocalization, tail flick, and escape behaviors, during and after the injection.

RESULTS: This study demonstrates that aversive behaviors induced by lateral tail vein injection were not changed by the preemptive application of EMLA cream. The aversive behaviors associated with lateral tail vein injection were significantly affected by the number of injection attempts and the individual's experience level.

CONCLUSIONS AND CLINICAL RELEVANCE: Topical EMLA cream did not reduce signs of aversive reaction to tail vein injection and thus we did not find support for its use in mouse training programs for tail vein injections.