A pharmacokinetic study of a topical anesthetic (EMLA®) in mouse soft tissue laceration

The use of topical anesthesia instead of injection of local anesthetics for managing soft tissue lacerations in the emergency situations may be a relief for both patients and surgeons. Topical anesthesia in the form of a cream eutectic mixture of local anesthetics (EMLA^®) containing 2.5% lidocaine and 2.5% prilocaine has been reported as an efficient anesthetic on skin before venipuncture anesthesia and as an alternative to injection anesthesia in some minor surgery situations. The aim of this study was to compare the pharmacokinetics of EMLA^® when applied in a laceration with topical skin application in the mouse. A total of 120 Albino Laboratory‐bred strain mouse (BALB‐c) male mice were divided into three groups with regard to application mode of EMLA^®. Group A: with laceration, 48 mice; Group B: on intact shaved skin, 48 mice; Group C: control group (24 mice) with same procedures but without application of EMLA^®. Blood levels were collected at 0, 10, 20, 30, 45, 60, 75, and 90 min post‐EMLA^® application. Plasma sample analysis was carried out by employing liquid chromatography coupled with tandem mass spectrometric (LC‐MS/MS) method, and the pharmacokinetic analysis of the mouse plasma samples was estimated by standard non‐compartmental methods. The pharmacokinetic parameters of lidocaine and prilocaine were significantly altered following EMLA^® application to lacerated mouse skin in contrast to intact skin. The absorption of lidocaine and prilocaine was rapid following application of EMLA^® to lacerated and intact mouse skin. Maximum drug plasma concentration (C_max) and area under the drug plasma concentration–time curve (AUC) values of lidocaine were significantly increased by 448.6% and 161.5%, respectively, following application of EMLA to lacerated mouse skin in comparison with intact mouse skin. Similarly, prilocaine's C_max and AUC values were also increased by 384% and 265.7%, respectively, following EMLA application to lacerated mouse skin, in contrast to intact skin. Further pharmacokinetic studies on different carriers of lidocaine/prilocaine are warranted before any firm conclusions for the clinic can be drawn.