EMLA cream

The text on this page is taken from an informal compilation of opinions of contributors to the online VOLE List. As such, they are not peer reviewed and may contain differences of opinion. Those wishing to contact the list may contact Adrian Smith.

Has anyone used EMLA as analgesic on an ongoing basis?

I have a group who would like to use it for mice with tendency to develop warts in sensitive areas. Ulcerations, excess size etc are clear endpoints, but we would like to further refine management for animals with lesions not yet at that stage.

I am not sure how often EMLA can be safely & effectively re-applied without risking arrhythmias etc. All I've used it for is (and all references I can find describe are) refining conduct of single procedures, blood samples etc.

I can’t answer your question I’m afraid but local anaesthetics are quite cytotoxic - think of cocaine.

I have never used it because it takes a certain amount of time after application for it to act. If I remember correctly, it is 20-30 minutes.

In this case, for blood samples, it is not effective if it is applied shortly before the sample is collected.

Duration of action is quite short as well (not much more than an hour from memory).  Could the use of NSAIDs such as meloxicam be considered?

I would not use it with rodents. It takes min 20 min to reach some effect. Mice and rats would certainly lick the cream off, ending up with numb mouths.

David et al. (2014) concluded that topical EMLA cream did not reduce signs of aversive reaction to tail vein injection and thus they did not find support for its use in mouse training programs for tail vein injections. This paper is behind a paywall, but a VOLE member says that the paper did not mention the application time specifically, but based on the Discussion it was probably 30-45 minutes.

Comment: I would say this is a reason to train inexperienced people on cadavers and models before allowing them near live animals. The PK of EMLA in mice is quite different when the skin in intact vs broken skin- see below. Also- in answer to your nay-sayers: Just because they didn’t find a difference or improvement with EMLA is not the same as proving that they are equivalent. That would be a different study design and different stats. I would still argue use of it (or other local anaesthetic) is beneficial and in line with the 3Rs - although I use Xylocaine 10mg spray on rabbit ears if I don’t want them to move before I prick them. I'm not a big fan of EMLA- but I don't like waiting and I don’t like its creamy consistency.

EMLA was used by Keeting et al. (2012) to study its effect and the use of a pain grimace scale when applying full-thickness tattoos to rabbits (see Facial expression analysis). They concluded: 'ear tattooing causes transient and potentially severe pain in rabbits, which is almost completely prevented by prior application of local anaesthetic cream. The Rabbit Grimace Scale developed appears to be a reliable and accurate way to assess acute pain in rabbits'.

When using EMLA on rat tails prior to venepuncture, the restraint itself may cause such a degree of distress that it prevents identification of a diffference from the placebo controls.