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Simona De Gregori,1 Manuela De Gregori,1–4 Nora Bloise,5,6 Dario Bugada,3,4,7 Mariadelfina Molinaro,1 Claudia Filisetti,8 Massimo Allegri,3,9 Michael E Schatman,3,10,11 Lorenzo Cobianchi12,13 1Clinical and Experimental Pharmacokinetics Unit, Fondazione IRCCS Policlinico San Matteo, Pavia, Italy; 2Pain Therapy Service, Fondazione IRCCS Policlinico San Matteo, Pavia, Italy; 3Study in Multidisciplinary Pain Research Group, Parma, Italy; 4Young Against Pain Group, Parma, Italy; 5Department of Molecular Medicine, Centre for Health Technologies, INSTM UdR of Pavia, University of Pavia, Pavia, Italy; 6Department of Occupational Medicine, Toxicology and Environmental Risks, Istituti Clinici Scientifici Maugeri, IRCCS, Lab of Nanotechnology, Pavia, Italy; 7Emergency and Intensive Care Department – ASST Papa Giovanni XXIII, Bergamo, Italy; 8“V. Buzzi” Children Hospital, Pediatric Surgery, Milan, Italy; 9Anesthesia and Intensive Care Service, IRCCS MultiMedica Hospital, Sesto San Giovanni, Milano, Italy; 10Research and Network Development, Boston Pain Care, Waltham, MA, USA; 11Department of Public Health and Community Medicine, Tufts University School of Medicine, Boston, MA, USA; 12General Surgery Department, Fondazione IRCCS Policlinico San Matteo, Pavia, Italy; 13Department of Clinical, Surgical, Diagnostic and Pediatric Sciences, University of Pavia, Pavia, Italy Background: The pharmacokinetic properties and clinical advantages of the local anesthetic chloroprocaine are well known. Here, we studied the pharmacokinetic profile of a new hydrogel device loaded with chloroprocaine to investigate the potential advantages of this new strategy for postoperative pain (POP) relief. Materials and methods: We performed both in vitro and in vivo analyses by considering plasma samples of four piglets receiving slow-release chloroprocaine. To quantify chloroprocaine and its inactive metabolite 4-amino-2-chlorobenzoic acid (ACBA), a HPLC–tandem mass spectrometry (HPLC-MS/MS) analytical method was used. Serial blood samples were collected over 108 hours, according to the exposure time to the device. Results: Chloroprocaine was consistently found to be below the lower limit of quantification, even though a well-defined peak was observed in every chromatogram at an unexpected retention time. Concerning ACBA, we found detectable plasma concentrations between T0 and T12h, with a maximum plasma concentration (Cmax) observed 3 hours after the device application. In the in vitro analyses, the nanogel remained in contact with plasma at 37°C for 90 minutes, 3 hours, 1 day, and 7 days. Chloroprocaine Cmax was identified 1 day following exposure and Cmin after 7 days, respectively. Additionally, ACBA reached the Cmax following 7 days of exposure. Conclusion: A thorough review of the literature indicates that this is the first study analyzing both in vivo and in vitro pharmacokinetic profiles of a chloroprocaine hydrogel device and is considered as a pilot study on the feasibility of including this approach to the management of POP. Keywords: postoperative outcome, hydrogel device, chloroprocaine, ACBA, pharmacokinetics

Massimo Allegri,1,2 Dario Bugada,1–3 Manuela De Gregori,2,4 Maria A Avanzini,5 Annalisa De Silvestri,6 Anna Petroni,7 Angelo Sala,7,8 Claudia Filisetti,9–11 Antonia Icaro Cornaglia,12 Lorenzo Cobianchi13,14 1Department of Medicine and Surgery, University of Parma, Parma 2SIMPAR Group (Study in Multidisciplinary PAin Research), 3Department of Anaesthesia and ICU, ASST Papa Giovanni XXIII, Bergamo, 4Pain Therapy Service, Fondazione IRCCS Policlinico San Matteo, 5Laboratory of Transplant Immunology/Cell Factory, IRCCS Foundation Policlinico San Matteo, 6Clinical epidemiology and Biometrics Unit, Fondazione IRCCS Policlinico San Matteo, Pavia, 7Department of Pharmacological and Biomolecular Sciences, University of Milan, Milan, 8I.B.I.M., C.N.R., Palermo, 9PhD School, University of Pavia, 10Department of Pediatric Surgery, Fondazione IRCCS Policlinico San Matteo, Pavia, 11Department of Pediatric Surgery, “V. Buzzi” Children’s Hospital, Milan, 12Department of Public Health, Experimental and Forensic Medicine, University of Pavia, 13Department of Surgical, Clinical, Paediatric and Diagnostic Science, University of Pavia, 14General Surgery 1, IRCCS Fondazione Policlinico San Matteo, Pavia, Italy Abstract: Continuous wound infusion (CWI) may protect from inflammation, hyperalgesia and persistent pain. Current local anesthetics display suboptimal pharmacokinetic profile during CWI; chloroprocaine (CP) has ideal characteristics, but has never been tested for CWI. We performed an animal study to investigate the pharmacokinetic profile and anti-inflammatory effect of CP during CWI. A total of 14 piglets received an infusion catheter after pararectal laparotomy and were randomly allocated to one of three groups: 5 mL/h infusion of saline (group A), CP 1.5% (group B) and CP 0.5% (group C). Blood sampling was performed to assess absorption and systemic inflammation at 0, 3, 6, 12, 24, 48, 72, 96, 102 and 108 hours. The wound and contralateral healthy abdominal wall were sampled for histological analyses. Absorption of CP from the site of infusion, evaluated as the plasmatic concentrations of CP and its metabolite, 4-amino-2-chlorobenzoic acid (CABA), showed a peak during the first 6 hours, but both CP and its metabolite rapidly disappeared after stopping CP infusion. Local inflammation was reduced in groups B and C (CP-treated p < 0.001), in a CP dose-dependent fashion. While CP inhibited in a dose-dependent manner pig mononuclear cells (MNCs) in vitro proliferation to a polyclonal activator, no effect on systemic cytokines’ concentrations or on ex vivo monocytes’ responsiveness was observed, suggesting the lack of systemic effects, in line with the very short half-life of CP in plasma. CP showed a very good profile for use in CWI, with dose-dependent local anti-inflammatory effects, limited absorption and rapid clearance from the bloodstream upon discontinuation. No cytotoxicity or side effects were observed. CP, therefore, may represent an optimal choice for clinical CWI, adaptable to each patient’s need, and protective on wound inflammatory response (and hyperalgesia) after surgery. Keywords: continuous wound infusion, pig model, chloroprocaine, pharmacokinetics, inflammation, postoperative pain