What are the considerations for switching an adult patient with chronic pain from Oxycontin (oxycodone) to M-eslon (methadone)?

Switching from OxyContin to M-Eslon (Methadone)

Methadone should only be prescribed by experienced clinicians due to its complex pharmacokinetics, highly variable conversion ratios (1:5 to 1:12 from oral morphine), long half-life, and risk of serious adverse effects including cardiac arrhythmias and respiratory depression. 1

Indications for Opioid Switching

Switch from OxyContin (oxycodone) to methadone when: 1

• Inadequate analgesia despite appropriate dose escalation of oxycodone
• Unmanageable adverse effects that cannot be controlled with symptomatic therapies
• Cost considerations, as methadone is significantly less expensive 1
• Renal impairment (eGFR <30 mL/min), since methadone is excreted fecally rather than renally 1

Critical Conversion Considerations

Conversion Ratios

The conversion from oxycodone to methadone requires two-step calculation: 1, 2

1. First convert oxycodone to oral morphine equivalents using 1:1.5 ratio (oxycodone is 1.5x more potent than morphine) 2
2. Then convert morphine to methadone using ratios of 1:5 to 1:12 or higher, depending on the prior opioid dose 1

The conversion ratio is dose-dependent: higher baseline opioid doses require more conservative ratios (approaching 1:12 or greater). 1

Dose Reduction for Incomplete Cross-Tolerance

Reduce the calculated methadone dose by 25-50% to account for incomplete cross-tolerance between opioids. 2 This is critical because methadone's unique pharmacology creates asymmetric tolerance patterns. 2

Switching Protocol

Step-by-Step Approach

Use a 3-day switch protocol followed by one-week titration period: 3

1. Calculate the equianalgesic methadone dose using the two-step conversion above
2. Reduce this calculated dose by 25-50% for safety 2
3. Initiate methadone while tapering oxycodone over 1-3 days 3
4. Titrate methadone dose over the following week based on pain control and adverse effects 3
5. Provide immediate-release opioid for breakthrough pain at 5-20% of total daily morphine equivalent dose 1

Monitoring Requirements

Evaluate patients within 24-48 hours initially, then weekly during titration: 2

• Pain intensity and functional status
• Opioid-related adverse effects (sedation, respiratory depression, nausea)
• Cardiac monitoring for QT prolongation, as methadone carries arrhythmia risk 1
• Signs of inadequate analgesia requiring dose adjustment 2

Special Populations and Contraindications

Renal Impairment

Methadone is preferred in severe renal disease (stages 4-5, eGFR <30 mL/min) because it is excreted fecally, unlike oxycodone which accumulates renally. 1, 2

Cardiac Risk

Screen for cardiac disease and QT prolongation before initiating methadone. Consider baseline ECG, especially in patients with: 1

• Pre-existing cardiac conduction abnormalities
• Concurrent QT-prolonging medications
• Electrolyte abnormalities

Hepatic Impairment

Use additional caution and longer dosing intervals in hepatic dysfunction, as decreased clearance can lead to toxic accumulation. 2

Common Pitfalls to Avoid

• Never use full equianalgesic ratios without dose reduction - incomplete cross-tolerance is universal 1, 2
• Do not start with extended-release formulations - use immediate-release methadone for initial titration 2
• Avoid switching without adequate trial of first opioid - ensure proper dose titration of oxycodone has been attempted first 2
• Do not overlook methadone's long half-life (24-36 hours), which complicates dose adjustments and increases accumulation risk 1
• Never prescribe methadone without experience - refer to pain specialists or palliative care if unfamiliar with methadone management 1

Comprehensive Assessment Required

Switching should not be a mere mathematical calculation but must include evaluation of: 1

• Underlying clinical situation and pain characteristics
• Current pain and adverse effect intensity
• Comorbidities (especially cardiac and renal function)
• Concomitant medications and potential drug interactions
• Pharmacokinetic factors that could limit drug effectiveness 1

Alternative Considerations

If methadone fails or is contraindicated, consider switching to: 2

• Fentanyl (transdermal or parenteral) - safer in renal disease 1
• Hydromorphone - with careful renal monitoring 1
• Buprenorphine (transdermal) - safer in renal disease 1

Long-Term Management

Once stabilized on methadone, serum concentrations remain stable over months without significant autoinduction of metabolism. 3 Minor dose adjustments may be needed, but major changes are uncommon after initial titration. 3, 4

Success rates: Approximately 59-75% of patients switched to methadone from other opioids achieve good pain relief, though 24% may discontinue due to adverse effects. 4, 5