Step-by-Step Guide to Convert Total Morphine Dose to Fentanyl Patch
To convert from total daily morphine dose to transdermal fentanyl patch, use a 60-100:1 morphine to fentanyl ratio and select the appropriate patch strength based on the conversion table. 1
Conversion Process
Step 1: Calculate the 24-hour morphine requirement
- Determine the total daily dose of oral morphine
- If the patient is on IV/SubQ morphine, multiply by 3 to get the oral morphine equivalent (1 mg IV/SubQ morphine = 3 mg oral morphine)
- If the patient is on another opioid (not morphine), first convert to oral morphine equivalent using standard conversion ratios
Step 2: Select the appropriate fentanyl patch strength
Use this conversion table from the NCCN guidelines 1:
| Transdermal Fentanyl | Oral Morphine | IV/SubQ Morphine |
|---|---|---|
| 25 mcg/h | 60 mg/day | 20 mg/day |
| 50 mcg/h | 120 mg/day | 40 mg/day |
| 75 mcg/h | 180 mg/day | 60 mg/day |
| 100 mcg/h | 240 mg/day | 80 mg/day |
Step 3: Apply conservative dosing principles
- For opioid-tolerant patients, consider reducing the calculated dose by 25-50% to account for incomplete cross-tolerance 1
- For opioid-naive patients, fentanyl patches are contraindicated - start with immediate-release opioids first 2
- For doses exceeding 100 mcg/h, multiple patches may be used 2
Step 4: Provide breakthrough pain medication
- Prescribe short-acting opioid rescue medication, particularly during the first 8-24 hours 1
- The breakthrough dose should be approximately 10-15% of the 24-hour total opioid dose
Step 5: Monitor and titrate
- Evaluate pain control after the patch has reached steady state (12-24 hours after application) 2
- Adjust the patch dose no more frequently than every 3 days based on breakthrough medication requirements 2
- The patch is typically worn for 72 hours, though some patients may require replacement every 48 hours 1
Example Conversion
For a patient taking 180 mg oral morphine daily:
- Calculate 24-hour morphine requirement: 180 mg oral morphine daily
- Select appropriate patch: 75 mcg/h fentanyl patch (180 mg oral morphine ≈ 75 mcg/h fentanyl)
- Consider reducing by 25% for incomplete cross-tolerance: 75 mcg/h × 0.75 = 56.25 mcg/h
- Round to nearest available patch strength: 50 mcg/h
- Provide breakthrough medication: Immediate-release morphine 15-30 mg every 4 hours as needed
- Monitor and adjust after 3 days based on breakthrough usage
Important Considerations
- Pain should be relatively well controlled on short-acting opioids before initiating fentanyl patches 1
- Fentanyl patches are NOT recommended for unstable pain requiring frequent dose changes 1
- Use only in opioid-tolerant patients 2
- Application of heat (fever, heating pads, electric blankets) can accelerate fentanyl absorption and should be avoided 1
- The FDA-approved conversion tables are conservative to minimize risk of overdose 2
- Patients may require 12-24 hours of short-acting opioids after patch application until therapeutic levels are reached 1
Special Populations
- For elderly patients or those with renal/hepatic impairment, use the lower end of the dosing range 3
- For patients with very high morphine requirements, consider using multiple patches 2
- When converting from continuous IV fentanyl to transdermal fentanyl, a 1:1 ratio is appropriate 1
Remember that these conversion ratios are approximate guidelines, and clinical judgment must be used to titrate to the desired response based on individual patient factors 1, 2.