What is the conversion dose from Xtampza (oxycodone) to MS Contin (morphine sulfate)?

Converting Xtampza (Oxycodone) to MS Contin (Morphine Sulfate)

Multiply the total daily Xtampza dose by 1.5 to calculate the morphine equivalent, then reduce this calculated dose by 25-50% to account for incomplete cross-tolerance before initiating MS Contin. 1, 2

Step-by-Step Conversion Algorithm

Step 1: Calculate Total Daily Oxycodone Dose

• Add up all Xtampza doses taken in 24 hours to determine the total daily oxycodone dose 1
• Example: If taking Xtampza 18 mg twice daily = 36 mg/day total oxycodone 1

Step 2: Apply the Conversion Factor

• Multiply the total daily oxycodone dose by 1.5 to convert to morphine milligram equivalents (MME) 1, 2
• The oxycodone-to-morphine potency ratio is established as 1:1.5 by the CDC 1, 2
• Example: 36 mg oxycodone × 1.5 = 54 mg morphine equivalents per day 1

Step 3: Reduce for Safety (Critical Step)

• Reduce the calculated morphine dose by 25-50% to account for incomplete cross-tolerance and individual pharmacokinetic variability 1, 3
• This reduction prevents overdosing due to asymmetric tolerance between different opioids 4
• Example: 54 mg × 0.5 to 0.75 = 27-40.5 mg morphine per day as starting dose 1

Step 4: Divide into Appropriate Dosing Schedule

• MS Contin is typically dosed every 12 hours (twice daily) 1
• Divide the reduced total daily dose by 2 for the individual dose 1
• Example: 40.5 mg ÷ 2 = approximately 20 mg MS Contin twice daily 1
• Round to available tablet strengths (15 mg, 30 mg, 60 mg, etc.) 1

Clinical Considerations

Breakthrough Pain Management

• Prescribe immediate-release morphine at 10-20% of the 24-hour MS Contin dose for breakthrough pain 1, 3
• Reassess within 24-48 hours and adjust the MS Contin dose based on breakthrough medication requirements 1, 3

Monitoring and Titration

• Closely monitor for respiratory depression, especially during the first 24-48 hours after conversion 3
• Be prepared to titrate upward if pain control is inadequate after the initial conservative dosing 1
• The conversion tables provide only approximate estimates and cannot account for individual genetic and pharmacokinetic variability 1, 2

Special Populations

• In renal impairment, use extreme caution with morphine due to accumulation of active metabolites (morphine-6-glucuronide and morphine-3-glucuronide) that can cause neurotoxicity 4, 2
• Consider alternative opioids like fentanyl or buprenorphine in patients with chronic kidney disease stage 4 or 5 (eGFR <30 mL/min) 4

Important Caveats

Why the Dose Reduction is Essential

• Individual response varies remarkably between opioids due to asymmetric tolerance, different receptor affinities, and pharmacokinetic profiles 4
• 10-30% of patients do not respond well to morphine and may require subsequent opioid rotation 4
• The conversion ratio is unpredictable in clinical practice, making conservative initial dosing mandatory 4

Route of Administration Differences

• If parenteral morphine becomes necessary, the oral-to-parenteral (IV or subcutaneous) ratio is 3:1 4, 3
• Example: 60 mg oral morphine = 20 mg IV/subcutaneous morphine 4