title: Dexmedetomidine dose-dependently enhances local anesthetic action of lidocaine.
abstract: OBJECTIVE
  The combination of α2-adrenoceptor agonists, such as dexmedetomidine (DEX) and clonidine, with local anesthetics has been found to extend the duration of peripheral nerve blocks, probably owing to the resultant local vasoconstriction in the peripheral nerves. However, because the clear elucidation of the effect of DEX requires examination of the local anesthetic effect with DEX alone and the combination of various concentrations of DEX with local anesthetics, we evaluated the local anesthetic effect of various concentrations of DEX alone and with a local anesthetic.
  
  
  METHODS
  The present study assessed the tail-flick (TF) latencies after injection of the appropriate drug in male Sprague-Dawley rats, using an epidural model that allowed constant pain stimulation intensity, dispersion of the anesthetic, and a precise injection site and dose. Lidocaine alone, lidocaine with 2.5-ppm DEX, lidocaine with 5.0-ppm DEX, lidocaine with 7.5-ppm DEX, and DEX alone were administered at the predetermined dose. The TF latency changes over time were compared using repeated measures analysis of variance (ANOVA). Comparisons among the groups were analyzed using ANOVA followed by a post hoc Dunnett's multiple comparison test or Tukey's multiple comparison test.
  
  
  RESULTS
  The addition of DEX to lidocaine increased the TF latency and dose-dependently prolonged its duration as follows: 0-ppm DEX, 20 minutes; 2.5-ppm, 40 minutes; 5.0-ppm, 40 minutes; and 7.5-ppm, 50 minutes. DEX alone did not change the TF latency.
  
  
  CONCLUSIONS
  Our results have demonstrated that DEX dose-dependently enhances the local anesthetic action of lidocaine in a rat TF model.
authors.affiliation: Assistant Professor, Department of Dental Anesthesiology, Field of Oral and Maxillofacial Rehabilitation, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan. Electronic address: ken2006anes@yahoo.co.jp.
authors.forename: Kentaro
authors.initials: K
authors.lastname: Ouchi
authors.affiliation: Professor Emeritus, Department of Anesthesiology, Kinki University Faculty of Medicine, Higashi-Osaka City, Japan.
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Koga
authors.affiliation: Professor and Chairman, Department of Anesthesiology, Kinki University Faculty of Medicine, Higashi-Osaka City, Japan.
authors.forename: Shinichi
authors.initials: S
authors.lastname: Nakao
authors.affiliation: Professor and Chairman, Department of Dental Anesthesiology, Field of Oral and Maxillofacial Rehabilitation, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan.
authors.forename: Kazuna
authors.initials: K
authors.lastname: Sugiyama
mesh_terms: D000759:Adjuvants, Anesthesia / Q000008:administration & dosage*; D058647:Adrenergic alpha-2 Receptor Agonists / Q000008:administration & dosage*; D000766:Anesthesia, Dental / Q000379:methods*; D000772:Anesthesia, Local / Q000379:methods*; D000779:Anesthetics, Local / Q000008:administration & dosage*; D000818:Animals; D020927:Dexmedetomidine / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D007268:Injections, Epidural; D008012:Lidocaine / Q000008:administration & dosage*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D000759:Adjuvants, Anesthesia; D058647:Adrenergic alpha-2 Receptor Agonists; D000779:Anesthetics, Local; D020927:Dexmedetomidine; D008012:Lidocaine