I saw some confusion recently as to which topical anesthetic to use for a laceration. In my experience the typical options are some stuff called EMLA and some other stuff called LET, but they are not interchangeable. Do you know the difference and which is indicated for what?

EMLA

EMLA stands for a “eutectic mixture of local anesthetics.” The local anesthetics in this case are lidocaine and prilocaine. The word “eutectic” refers to a situation where a mixture of two substance results in a combination whose melting point is lower than that of either of the two substances on their own. I’m dancing on the edge of my knowledge base here, but the point is that in this case, the mixture of these two solids is liquid at room temperature. The solution is emulsified into a cream that can be applied to and penetrate intact skin.

EMLA could be used on the skin over a venipuncture site, a lumbar puncture site, or over an abscess prior to incision and drainage. It would not be used for laceration repair as that involves non-intact skin.

EMLA is applied by placing the desired amount over the skin surface of interest then covering that dollop with an occlusive dressing like a Tegaderm or Opsite. For good effect, EMLA needs to sit for 45 minutes to an hour. Clearly this can limit its usefulness in emergent situations.

LET

LET stands for Lidocaine, Epinephrine, and Tetracaine. It comes either as an aqueous solution or a gel and is stored in a refrigerator. It can be applied to cut skin and therefore is very useful for laceration repair, especially in children. The epinephrine induces vasoconstriction, which leads to a blanching of the skin that the solution is applied to – a nice indication that it is working.

There is some variation on how exactly to apply LET. My practice is to saturate a cotton ball then wedge that into the laceration and secure it with paper tape. Fairly frequent rechecks to be sure the cotton ball has not migrated while waiting for it to work are a must.

LET needs to be applied for about 20 minutes to work well, and may need a second application in some instances. Also, the wound needs to have been cleared of clot and debris prior to its application as those will keep the solution from coming into contact with the tissue. Personally, I may sneak in some subcutaneous lidocaine ‘just to be sure’ before placing the sutures in cases where there is any doubt about how robust of a block the LET provided – but even in those cases, the LET will take the sting out of the subcutaneous injection. On the other hand, I’ve sewn lacerations on my own daughter with just LET. This is a very reasonable option in many cases.

The short version

EMLA is a cream that can be used on intact skin and needs about an hour for good effect. LET is available in a liquid or a gel preparation and is for anesthesia involving non-intact skin. LET takes about 20 minutes to take effect.