title: Prolonged suppression of postincisional pain by a slow-release formulation of lidocaine.
abstract: BACKGROUND
  Postoperative pain can occur despite nerve blocks during the surgical period. Here we tested Xybrex (Orthocon, Inc., Irvington, NY), a slow-release formulation of lidocaine that blocks rat sciatic nerve for 1-2 days, for its ability to suppress postincisional pain.
  
  
  METHODS
  A plantar paw incision was made in rats, either along the midline (Brennan model) or at the lateral edge, 30 min after different treatment groups received either lidocaine (0.2 ml, 2%) or Xybrex implant at the ipsilateral sciatic nerve or Xybrex at the contralateral sciatic nerve. Behavioral testing by von Frey filaments occurred at 2 and 6 h postoperatively and for the next 10 postoperative days. The fractional response (paw withdrawal responses per 10 pokes) was scored at each time.
  
  
  RESULTS
  Mechanosensitivity from the Brennan paw incision was reduced throughout the postoperative period by ipsilateral Xybrex, although lidocaine injection almost had no effect. Contralateral Xybrex had a weaker but still significant antihyperalgesic effect, converging to that from ipsilateral Xybrex at postoperative day 2. Xybrex at the nuchal midline reduced allodynia for only postoperative days 1-3, whereas hyperalgesia was reduced continuously after postoperative day 2. Hyperalgesia from the lateral incision was also reduced by ipsilateral Xybrex but not by contralateral Xybrex.
  
  
  CONCLUSIONS
  Implants of slow-release lidocaine formulations are most effective against postincisional pain when placed at the ipsilateral nerve innervating the area of incision. Contralateral nerve implants are somewhat less effective, probably acting by releasing lidocaine into the systemic circulation. There appears to be a differential role of central sensitization between postincisional allodynia and hyperalgesia.
authors.affiliation: Tufts School of Medicine, Boston, Massachusetts, USA.
authors.forename: Chi-Fei
authors.initials: CF
authors.lastname: Wang
authors.forename: Carlo
authors.initials: C
authors.lastname: Pancaro
authors.forename: Peter
authors.initials: P
authors.lastname: Gerner
authors.forename: Gary
authors.initials: G
authors.lastname: Strichartz
mesh_terms: D000779:Anesthetics, Local / Q000008:administration & dosage / Q000627:therapeutic use*; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D003692:Delayed-Action Preparations; D004195:Disease Models, Animal; D004343:Drug Implants; D005500:Follow-Up Studies; D008012:Lidocaine / Q000008:administration & dosage / Q000627:therapeutic use*; D008297:Male; D010149:Postoperative Pain / Q000517:prevention & control*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012584:Sciatic Nerve / Q000187:drug effects
chemical_list: D000779:Anesthetics, Local; D003692:Delayed-Action Preparations; D004343:Drug Implants; D008012:Lidocaine