DRUG TREATMENT  -  Common Opioids   
Methadone

Long acting, unique lack of euphoria, inexpensive
  • Mu receptor agonist, NMDA receptor antagonist
  • effective for neuropathic pain 
  • less opioid-induced tolerance and hyperalgesia 
  • high inter-individual variability 
Biphasic renal elimination 
  • a-elimination (6-8 hours), analgesic duration 
  • ß-elimination (30-60 hours), prevents withdrawal symptoms 
Switching from another opioid 
  • Stop current opioid 
  • Start methadone, dividing calculated starting dose into Q8H doses 
  • 5% of total daily dose may be given Q6H  PRN breakthrough pain 
  • Adjust dose only every 5 to 14 days 
Opioid-naïve patient:    2.5 to 10 mg Q8H

Key patient education point: same pill size as oxycodone, yet 5 mg methadone 3-4 times as potent as 5 mg oxycodone

QT prolongation and torsade de pointes 
  • higher doses (200 mg), known risk factors for arrhythmia, hypokalemia and other medications that prolong QT 
  • QTc of 450-500 range should raise caution flag to lower dose or look at drug interactions; >500 could be life threatening