One of our readers of the Question of the Week asked to have this question addressed. Here it is.
The acronym EMLA stands for eutectic mixture of local anesthetics. This 5% cream contains 2.5% lidocaine and 2.5% prilocaine. Eutectic means that the primary ingredients, lidocaine and prilocaine, are solid at room temperatures; however, when they are combined, they form a liquid. This creates an oil-in-water emulsion so that there are higher concentrations of the active ingredients per emulsion droplet. This aids in skin penetration of the local anesthetics.
EMLA is applied topically and is typically used as a topical dermal anesthetic prior to minor procedures such as venipuncture. The package insert for the product states that the depth of anesthesia achieved is 2 mm after 60 minutes of application and 3 mm after 120 minutes. It is approved for use over intact skin; however, there have been studies examining its use for pretreatment of lacerations. One study (Acad Emerg Med 2001;8:223-30) compared EMLA to a LET (lidocaine, epinephrine, tetracaine) solution and the LET solution had more anesthesia to needlestick than EMLA. There were no differences between the products in the median amount of pain from lidocaine infiltration.
Toxicity from topical skin application of EMLA is rarely reported. There have been cases of neurotoxicity (most likely from lidocaine’s metabolite) and methemoglobinemia. Most of these cases involve patients who used large doses (more than recommended by the manufacturer) or patients who had an underlying integument problem such as eczema, atopic dermatitis, or extensive molluscum contagiosum. Either of these scenarios may result in increased absorption and systemic bioavailability.
Question prepared by: Saralyn Williams, M.D. Medical Toxicologist
I am interested in any questions you would like answered in the Question of the Week. Please email me with any suggestion at donna.seger@vanderbilt.edu
Donna Seger, M.D.
Medical Director
Tennessee Poison Center