Lidocaine/prilocaine

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 AstraZeneca under the trade name EMLA (an abbreviation for eutectic mixture of local anesthetic).

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Eutectic mixture

Separately, lidocaine and prilocaine are solid bases. When mixed together in equal quanitites 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 16°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.

Clinical use

Indications

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.

EMLA cream is also used in the treatment of premature ejaculation. It is applied 20 minutes prior to sex

Dosage forms

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.

See also

• Eutectic point
• Lidocaine
• Prilocaine