Eutectic Mixture of Local Anesthetics

Cordoni, A., and Cordoni, L. E. (2001), Eutectic mixture of local anesthetics reduces pain during intravenous catheter insertion in the pediatric patient, Clin. J. Pain, 17, 115-118. 

Sinisterra S, Miravet E, Alfonso 1, Soliz A, Papazian O. Methemoglobinemia in an infant receiving nitric oxide after the use of eutectic mixture of local anesthetic. J Pediatr 2002 141(2) 285-6. 

This Eutectic Mixture of Local Anesthetics is used successfully in many brief but painful minor operations. EMLA has been tried as a local anesthetic for phenol peels. However, the following arguments should restrict its use in this indication ... 

Juhlin L, Hagglund G, Evers H. Absorption of lidocaine and prilocaine after application of a eutectic mixture of local anesthetic (EMLA) on normal and diseased skin. Acta Derm Venerol (Stock) 1989 69 18-22. 

Generic Names topical lidocaine/prilocaine, topical lidocaine/tetracaine, tetracaine gel, 4% liposomal lidocaine, 1,1,1,3,3-pentafluoropro-pane and 1,1,1,2-tetrafluoroethane Trade/Proprietary Names EMLA (Eutectic Mixture of Local Anesthetics), Synera", Ametop Gel , LMX-4 , PainEase (vapocoolant spray)... 

Plank RM, Kubiak DW, Abdullahi RB, Ndubuka N, Nkgau MM, Etapaah-Siakwan F, et al. Loss of anatomical landmarks with eutectic mixture of local anesthetic cream for neonatal male circumcision. J Pediafr Urol 2013 9(l) e86-90. 

EMLA cream (lidocaine 2.5% and prilocaine 2.5%) consists of a eutectic mixture of focal anesthetics. It is used to provide topical anesthetic to intact skin. Other topical preparations are effective only on mucosal surfaces. EMLA has been shown to reduce pain on venipuncture and provide substantial anesthesia for skin graft donor sites. No significant local or systemic toxicity has been demonstrated. 

Since absorption of local anesthetics through the skin is enhanced by heat, a topical patch with an intrinsic heating system was developed [4], This incorporates a controlled heat-assisted delivery system that is physically separated from a eutectic mixture of 70 mg of lidocaine and 70 mg of tetracaine. The surface area of the entire Synera patch is approximately 50 cm, 10 cm of which is active. 

Local anesthetics or sedation are not required for the CROSS. Generally, patients feel bearable prickling and burning sensation during the procedure. If needed, a topical anesthetic cream, such as EMLA cream (eutectic mixture of 2.5% lidocaine-HCl and 2.5% prilocaine ... 

Mixing lidocaine base and prilocaine base in equal parts, at room temperature, gives a eutectic mixture. This mixture is emulsified in a base that consists mainly of water and polyoxyethylene castor oil, and the anesthetics are added to the oily phase. Phenol has an excellent oil/water partition coelEcient. The oils lower the toxicity of phenol, but also slow down its rate of penetration as well as absorption of the local anesthetics. There is a competition between the phenol solution and the EMLA, which changes the activity and penetration of the combined molecules. 

Lidocaine [2-(diethylamino)-N-(2, 6-dimethylphenyl) acetamide monohydrochloride] is the most commonly used amino amide-type local anesthetic. Lidocaine is very lipid soluble and, thus, has a more rapid onset and a longer duration of action than most amino ester-type local anesthetics, such as procaine and tetracaine. It can be administered parenterally (with or without epinephrine) or topically either by itself or in combination with prilocaine or etidocaine as a eutectic mixture that is very popular with pediatric patients. The use of lidocaine-epinephrine mixtures should be avoided, however, in areas with limited vascular supply to prevent tissue necrosis. Lidocaine also frequently is used as a class IB antiarrhythmic agent for the treatment of ventricular arrhythmias, both because it binds and inhibits sodium channels in the cardiac muscle and because of its longer duration of action than amino ester-type local anesthetics. 

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