Comparative topical anaesthesia of EMLA and liposome-encapsulated tetracaine

The eutectic mixture of local anaesthetics (EMLA) provides effective topical anaesthesia after a minimum of 60 to 90 min application. Since liposome-encapsulated tetracaine (LET) can provide rapid dermal penetration, the goal of this study was to compare the local anaesthetic effects of EMLA and LET in human volunteers after 60 min application.

After obtaining institutional approval and informed consent, healthy volunteers were recruited in a double blind, crossover, randomized trial. The study creams (0.5 ml EMLA and 0.5 ml LET 5%) were applied randomly to opposite arms for 60 min. The discomfort of i.v. catheterization was assessed using a visual analogue pain score (VAS). Cutaneous side effects of the creams were recorded.

Sixty-one subjects were studied. Twenty-one were excluded because of technical difficulties. Forty subjects completed the study and were included in the data analysis. The mean ( +/- SD) VAS was lower for LET than for EMLA (10.9 +/- 9.0 mm vs 22.7 +/- 17.1 mm, P < 0.001). Erythema secondary to vasodilatation occurred more frequent in the LET group than in the EMLA group (33 vs 3, P < 0.001). One subject with a history of atopy developed a rash at the LET application site.

Liposome-encapsulated tetracaine can provide a more effective topical anaesthesia than EMLA for intravenous catheterization after 60 min application. Clinical evaluations are necessary to determine the efficacy and safety of LET in providing topical anaesthesia for various invasive percutaneous procedures in other patient populations.