Evaluation of the Depth and Duration of Anesthesia From Heated Lidocaine/Tetracaine (Synera) Patches Compared With Placebo Patches Applied to Healthy Adult Volunteers

Background: The heated lidocaine/tetracaine patch (Synera; ZARS Pharma, Inc, Salt Lake City, UT) is among the local topical anesthetic formulations used to prevent, procedural pain. This study was conducted to determine the depth and duration of anesthesia provided by the patch and to evaluate safety and tolerability. Methods: This randomized, double-blind, placebo-controlled, 2-period crossover study was conducted in healthy subjects. Subjects were randomized to receive either the heated lidocaine/tetracaine patch (active patch) in period 1 and placebo patch in period 2 or vice versa. Patches were applied for 30 mins to the volar aspect of the forearm. Pain and sensory depths were measured at baseline and at 30, 60, 90, and 150 mins after patch application. Duration of anesthesia was measured at 40, 70, 110, and 130 mins after patch application by evaluating thermal and mechanical sensation. Results: A total of 25 subjects were enrolled in the study. Twenty-four subjects completed the study. Pain and sensory depths with the active patch were greater than with placebo (P < 0.001) at all postdose time points. Maximum mean pain depth achieved with the active patch was 8.22 mm; anesthesia lasted at least 100 mins after patch removal. Cool and warm sensations and hot pain thresholds were increased compared with placebo (P < 0.001). Light touch and pinprick were detectable by most subjects. Conclusions: The heated lidocaine/tetracaine patch is well tolerated, and it provides favorable depth and duration of anesthesia without significant sensory loss for superficial venous access and minor dermatological procedures after a 30-min application.