Evaluation of Ropivacaine and 3-OH-Ropivacaine Pharmacokinetics Following Interpectoral Nerve Block via LC-MS/MS-A Pilot Study.

Regional anesthesia techniques such as the ultrasound-guided PECS II (pectoral nerve block) block are increasingly employed to optimize perioperative analgesia while minimizing systemic anesthetic exposure. Ropivacaine is commonly used for its favorable pharmacological profile; however, clinical data on its pharmacokinetics and systemic metabolite behavior following interpectoral administration remain limited. This study aimed to characterize the plasma concentration-time profile of ropivacaine and its main active metabolite, 3-OH-ropivacaine, in patients undergoing interpectoral nerve block, using a validated LC-MS/MS (liquid chromatography coupled with mass spectrometry) method. Venous blood samples were collected from 18 patients at predefined time points (0, 1, 3, 6, and 24 h) following a PECS II block performed with a ropivacaine-lidocaine mixture. Plasma concentrations were quantified via a validated LC-MS/MS protocol in accordance with FDA (Food and Drug Administration) and EMA (European Medicines Agency) guidelines. Pharmacokinetic parameters were derived using non-compartmental analysis. Ropivacaine reached a mean peak plasma concentration (Cmax-maximum concentration) of 167.5 ± 28.3 ng/mL at 1.3 ± 0.2 h (Tmax-maximum time). The metabolite 3-OH-ropivacaine peaked at 124.1 ± 21.4 ng/mL at 2.3 ± 0.3 h. The terminal elimination half-life was 19.4 ± 2.8 h for ropivacaine and 29.2 ± 3.1 h for its metabolite. Plasma levels demonstrated prolonged systemic exposure with predictable pharmacokinetics. The PECS II block using ropivacaine results in sustained systemic levels of both the parent drug and its primary metabolite, supporting its role in prolonged perioperative analgesia. These data provide a pharmacokinetic foundation for personalized regional anesthesia protocols. This strategy facilitates the adaptation of anesthetic protocols to the individual characteristics of each patient, aligning with the principles of personalized medicine, particularly in patients with altered metabolic capacity.