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Lidocaine/prilocaine is a eutectic mixture of equal quantities (by weight) of lidocaine and prilocaine. A 5% emulsion preparation, containing 2.5% each of lidocaine/prilocaine, is marketed by APP Pharmaceuticals under the trade name EMLA (an abbreviation for Eutectic Mixture of Local Anesthetics).
Separately, lidocaine and prilocaine are solid bases. When mixed in equal quantities by weight, however, they form a eutectic mixture – that is the melting point of the mixture is lower than the melting points of the individual components. The lidocaine/prilocaine eutectic mixture is an oil with a melting point of 18°C, thus can be formulated into preparations without the use of a non-aqueous solvent. This allows higher concentrations of anaesthetic to be formulated into the preparation and maintained during application.
The lidocaine/prilocaine combination is indicated for dermal anaesthesia. Specifically it is applied to prevent pain associated with intravenous catheter insertion, blood sampling, superficial surgical procedures; and topical anaesthesia of leg ulcers for cleansing or debridement. Also, it can be used to numb the skin before tattooing as well as electrolysis and laser hair removal.
Researchers have shown that a new topical spray, consisting of an aerosol formulation of lidocaine and prilocaine, applied on the penile skin five minutes prior to intercourse is effective for treating premature ejaculation without adversely affecting the sensation of ejaculation.
Lidocaine/prilocaine eutectic mixture is marketed as a 5% oil-in-water emulsion incorporated in a cream base (EMLA cream) or a cellulose disk (EMLA patch). The cream is applied under an occlusive dressing, while the patch incorporates an occlusive dressing to facilitate absorption of lidocaine and prilocaine into the area where anaesthesia is required. Local dermal anaesthesia is achieved after approximately 60 minutes, whereupon the occlusive dressing (or patch) is removed. The duration of anaesthesia is approximately two hours following removal of the occlusive dressing.
It is important to note that E. Fougera & Co., makers of the generic cream widely used in the United States as Lidocaine and Prilocaine Cream, 2.5%/2.5%, recommends different timing for application of the cream as well as length of anesthesia. They state the cream must be applied at least one hour before the start of a routine procedure and for two hours before the start of a painful procedure. Additionally, they state that the duration of effective skin anesthesia will be at least one hour after removal of the occlusive dressing.
- Heinen et al 2003
- Lidocaine and Prilocaine Cream, 2.5%/2.5%, package insert. E. Fougera & Co. package insert. Melville, New York, 9/2007.
- The United States Pharmacopeial Convention. "Revision Bulletin: Lidocaine and Prilocaine Cream–Revision to Related Compounds Test". Retrieved 10 July 2009.