Plasma levels of a methadone constant rate infusion and their corresponding effects on thermal and mechanical nociceptive thresholds in dogs.BACKGROUND
 The present study aimed to collect pharmacokinetic data of a methadone continuous rate infusion (CRI) and to investigate its effect on mechanical and thermal nociceptive thresholds.  Mechanical and thermal thresholds, as well as vital parameters and sedation were measured during CRI and for further 24 h.  Percentage thermal excursion (%TE) increased significantly from baseline (BL) until 3 h after discontinuation of CRI in M. Within P and between treatment groups differences were not significant.  Bradycardia and hypothermia occurred in M during drug administration and dogs were mildly sedated for the first 47 h.  Effective methadone plasma concentrations for thermal and mechanical antinociception were above 17 ng ml- 1.


 Main side effects were related to gastrointestinal tract, hypothermia, bradycardia and sedation.
THERM