Methadone

Methadone is a full mu-agonist that provides good analgesia when given intravenously. Methadone also provides noncompetitive NMDA (n-methyl-d-aspartate) antagonist properties, which can be helpful in treating significant pain in our patients. Methadone does not lead to significant histamine release that can be seen with drugs such as morphine, etc. Methadone also provides good analgesia with less sedative effects and lower incidence of emesis, making it a preferable choice in some patients compared to hydromorphone or morphine.

Methadone is very similar in potency compared to morphine (1-1.5x potent). As with other full mu-agonists, methadone is completely reversible by naloxone in the case of an emergency. The half-life is 2-3 hours therefore it is dosed similarly to hydromorphone at every 4-6 hours. Methadone can be given intravenously, subcutaneous or intramuscularly.

Product formulation

• 20ml vial – concentration 10 mg/ml

Dosing suggestions

  • Dogs:
    • Premedication dosing: 0.1-0.6 mg/kg in combination with an anxiolytic/sedative
    • Intermittent analgesia: 0.1-1.0 mg/kg IV every 4-6 hours
    • CRI: Loading dose 0.1-0.2 mg/kg IV, then 0.12 mg/kg/hr
  • Cats:
    • Premedication dosing: 0.1-0.6 mg/kg in combination with an anxiolytic/sedative
    • Intermittent dosing: 0.05-0.5 mg/kg IV every 4-6 hours
    • CRI: Loading dose 0.1-0.2 mg/kg IV, then 0.12 mg/kg/hr
  • Can be combined other drugs (with variable doses) for pre-anesthetic medication or for continued analgesia for hospitalized patients.

Side effects

  • Panting, whining
  • Mild sedation
  • GI signs: vomiting, defecation or constipation
  • Cardiorespiratory: bradycardia, respiratory depression at higher doses.

Contraindications

  • Pregnancy, especially late-term pregnancy
  • Dose adjustments may need to be made for compromised animals

Control schedule class

Class II (similar to Hydromorphone, Morphine, etc.)

Additional resources

Last updated: 2017-11-15