Efficacy and duration of analgesia from a sustained-release lidocaine sheet in humans

Abstract

We have synthesized a sustained-release lidocaine sheet (SRLS) and injectable sustained-release lidocaine particles (SRLP) using biodegradable polymers. In the present study, we performed an exploratory first clinical trial of the SRLS in healthy volunteers as a prelude to patient administration. This trial is meant as an initial intervention in ultimately developing and refining the SRLP. We evaluated the intensity and duration of analgesia of the SRLS compared with 8% lidocaine spray. In Protocol 1, we applied the SRLS piece to the mucous membrane of the nasal vestibule. We examined the local pain threshold over 72 h after administration, and removed the SRLS after 72 h. Individuals that finished Protocol 1 underwent Protocol 2, in which we applied 8% lidocaine spray. Twelve volunteers were enrolled and seven of these volunteers finished Protocol 1. All seven individuals who completed Protocol 1 also completed Protocol 2. The mean pain thresholds were 32 g, 78 g, 90 g, 90 g, 87 g, and 87 g at pre-administration and 4 h, 10 h, 24 h, 48 h, and 72 h after administration, respectively, in Protocol 1, and 36 g, 85 g, 49 g, and 33 g at pre-administration and 15 min, 2 h, and 4 h, respectively, in Protocol 2. A sustained-release lidocaine using biodegradable polymers was applied as a sheet in humans for the first time in the world. It maintained significant analgesia for 72 h without major toxicities. Furthermore, degree of analgesia provided by the SRLS throughout the entire study was similar to that provided by the 8% lidocaine spray. It may suitable for management of postoperative pain especially in outpatients.