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Introduction: Erector spinae plane (ESP) block is an emerging interfascial block with a wide range of indications for perioperative analgesia and chronic pain treatment. Recent studies have focused their attention on mechanisms of action of ESP block. However, the pharmacokinetics of drugs injected in ESP is, as of now, uninvestigated. The aim of this brief report is to investigate the pharmacokinetics of lidocaine in a series of 10 patients., Methods: We are reporting a case series of 10 patients undergoing bilateral ESP block for multilevel lumbar spine surgery.ESP was performed with 3.5 mg/kg of lidocaine based on ideal body weight. Lidocaine concentration was dosed at 5, 15, 30 min and at 1, 2 and 3 hours., Results: T max was 5 min for all the patients. C max ranged from 1.2 to 3.8 mg/L (mean: 2.59 mg/L). AUC 0-3 was high (76%, on average) suggesting an almost complete bioavailability. Age had a negative correlation with T½ of lidocaine., Conclusions: Lidocaine pharmacokinetic after ESP block is well-described by a two-compartment model with a rapid and extensive rate of absorption. Nevertheless, its peak concentrations never exceeded the accepted toxicity limit. Elimination half-life was slightly prolonged, probably due to the advanced age of some patients., Competing Interests: Competing interests: None declared., (© American Society of Regional Anesthesia & Pain Medicine 2021. No commercial re-use. See rights and permissions. Published by BMJ.)