title: Electrocardiographic evaluation and degree of sedation with three doses of methadone in healthy dogs [corrected].
abstract: OBJECTIVE
  The present study aimed to investigate the influence of methadone on cardiorespiratory parameters, electrocardiogram and clinical sedation in dogs. Further possible side effects are reported.
  
  
  METHODS
  Prospective experimental cross-over study. DOGS: Eight, 1-4-year-old, various breeds of dogs of both genders weighing 9-36 kg.
  
  
  METHODS
  Each dog was treated three times: methadone 0.3 mg kg(-1) (M0.3), 0.5 mg kg(-1) (M0.5) and 1.0 mg kg(-1) (M1.0) intramuscularly. Respiratory rate, heart rate and arterial blood pressure were recorded as well as electrocardiographic evaluation of lead II. Clinical sedation in each treatment received a score (0-3) after drug administration and at 30 minute intervals until scores and measurements returned to baseline values.
  
  
  RESULTS
  A significant decrease in heart rate was seen with each dose of methadone and bradycardia (HR<60 bpm) was noted in a few dogs at each dose. A clinically significant arrhythmia occurred in one dog at 1 mg kg(-1) that required reversal with butorphanol. There was no significant difference in SAP, MAP and DAP between treatments. Some side effects such as salivation, defecation, vocalization and panting, after administration of methadone were observed. There were no differences in mean values of heart rate, P-wave and QRS complex duration and QT interval between treatments.
  
  
  CONCLUSIONS
  Methadone administration was associated with panting and a decrease in heart rate at all doses tested in this study. The cardiac rhythm should be monitored carefully in dogs when methadone is administered on its own, especially at higher doses.
authors.affiliation: Departament of Internal Clinical, Surgery and Reproduction, Faculdade de Medicina Veterinária de Araçatuba, UNESP, Araçatuba, Brazil.
authors.forename: Thais M
authors.initials: TM
authors.lastname: Menegheti
authors.forename: Juliana T
authors.initials: JT
authors.lastname: Wagatsuma
authors.forename: Acácio D
authors.initials: AD
authors.lastname: Pacheco
authors.forename: Beatriz
authors.initials: B
authors.lastname: Perez
authors.forename: Cynara M
authors.initials: CM
authors.lastname: Pacheco
authors.forename: Caio J X
authors.initials: CJ
authors.lastname: Abimussi
authors.forename: Paulo P S
authors.initials: PP
authors.lastname: dos Santos
authors.forename: Valéria N L
authors.initials: VN
authors.lastname: de Souza Oliva
mesh_terms: D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000139:chemically induced / Q000662:veterinary*; D016292:Procedural Sedation / Q000662:veterinary*; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D004562:Electrocardiography / Q000662:veterinary*; D008691:Methadone / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D000701:Analgesics, Opioid; D008691:Methadone
keywords: cardiac arrhythmias; dog; intramuscular; opioid