Plasma concentrations of lignocaine and prilocaine after a 24-h application of analgesic cream (EMLA®) to leg ulcers

Background Although the lignocaine (lidocaine)–prilocaine cream EMLA® has been extensively studied for the relief of acute treatment-related pain from sharp leg ulcer debridement, no data exist on systemic absorption from prolonged application in patients with chronically painful ulcers. Objectives To study the plasma concentrations of lignocaine and prilocaine resulting from prolonged application of EMLA to leg ulcers. Methods A single 24-h application of 5–10 g (median 6·75) of EMLA was given to 10 patients with painful leg ulcers measuring 50–100 cm2. Venous blood samples, drawn between 0·5 and 27 h after cream application, were analysed by gas chromatography using a nitrogen-sensitive detector. Results The peak plasma levels were in the range 185–705 ng mL−1 and 62–277 ng mL−1 for lignocaine and prilocaine, respectively, and were observed 2–4 h (in one patient 6–8 h) after application. The peak plasma concentration of lignocaine, but not of prilocaine, increased significantly with increasing dose. The cream was well tolerated by the patients. Conclusions The results indicate that a 24-h application of 5–10 g EMLA results in peak plasma concentrations of the two local anaesthetics, which combined are less than one-fifth of those associated with toxic reactions. The analgesic efficacy of EMLA for the relief of chronic ulcer pain deserves further study.