About this Calculator

The Fentanyl Patch Conversion Calculator is a clinical decision support tool designed for healthcare professionals to calculate equianalgesic doses when switching patients to or from transdermal fentanyl patches. It facilitates safe and effective pain management transitions by converting dosages from various opioids to a fentanyl patch and vice versa, incorporating essential safety reductions for incomplete cross-tolerance.

Outputs Explained

The calculator provides tailored outputs based on the conversion direction:

Converting TO Fentanyl Patch

• Total 24h Oral Morphine Equivalent (OME): The combined daily dose of all current opioids, standardized to oral morphine.
• Reduced OME: The OME after applying a safety reduction (typically 25-50%) to account for incomplete cross-tolerance.
• Calculated Fentanyl Dose: The theoretical patch strength in mcg/hr based on the reduced OME.
• Recommended Commercial Patch: The closest available commercial patch size(s) to the calculated dose.

Converting FROM Fentanyl Patch

• Equivalent 24h OME: The oral morphine equivalent of the current fentanyl patch dose.
• Total Daily Dose of New Opioid: The calculated total 24-hour dose of the selected target opioid.
• Suggested Dosing Regimen: Example dosing schedules (e.g., q4h or q6h) for the new opioid.
• Recommended Breakthrough Dose: A calculated dose for managing breakthrough pain, typically 10-15% of the new total daily dose.

How to Use the Tool

Follow these steps for an accurate calculation:

To Convert TO a Fentanyl Patch:

1. Select the “Convert TO Fentanyl Patch” mode.
2. For each current opioid, enter the Dose (mg), Route (Oral or IV/IM/SC), and Frequency. Use the “+ Add Another Opioid” button for patients on multiple medications.
3. Choose an appropriate Incomplete Cross-Tolerance Reduction percentage. A 25-50% reduction is standard practice for safety.
4. Click “Calculate Dose” to view the recommended fentanyl patch strength.

To Convert FROM a Fentanyl Patch:

1. Select the “Convert FROM Fentanyl Patch” mode.
2. Choose the patient’s Current Fentanyl Patch strength (mcg/hr).
3. Select the desired Target Opioid and Target Route from the dropdown menus.
4. Click “Calculate Dose” to see the equivalent daily dose and suggested regimen for the new opioid.

Dosing Overview

Transdermal fentanyl is a potent opioid agonist indicated for the management of pain in opioid-tolerant patients severe enough to require daily, around-the-clock, long-term opioid treatment. Patches are typically applied and worn for 72 hours. Due to a significant delay in absorption, analgesic effects may not be seen for 12-24 hours after the first application. It is crucial to manage baseline pain with short-acting analgesics during this initial period.

Switching Opioids

When switching between opioids, the concept of incomplete cross-tolerance is paramount. Patients may be more sensitive to a new opioid than predicted by standard equianalgesic tables. Therefore, a dose reduction of 25-50% is a critical safety measure when converting to fentanyl. When converting from a fentanyl patch, the patch should be removed and the first dose of the new opioid administered. Due to fentanyl’s long half-life, significant serum concentrations persist for hours after removal; some guidelines suggest leaving the patch on for 8-12 hours after the first dose of the new opioid to ensure adequate analgesia during the transition.

Patch Detachment or Missed Dose

If a patch falls off before 72 hours, a new patch should be applied to a different skin site immediately. The new patch should be considered a replacement for the full 72-hour dosing interval. The dosing schedule should be reset based on when the new patch was applied. Do not use supplemental tape or other adhesives to try to re-apply a used patch.

Safety Alerts

Transdermal fentanyl carries significant risks and is subject to multiple FDA Black Box Warnings:

• Addiction and Misuse: High potential for abuse, which can lead to overdose and death.
• Respiratory Depression: Serious, life-threatening, or fatal respiratory depression may occur.
• Drug Interactions: Concomitant use with benzodiazepines or other CNS depressants increases the risk of profound sedation and respiratory depression. Use with CYP3A4 inhibitors can cause a fatal overdose.

Frequently Asked Questions

Why is a dose reduction necessary when switching opioids?

A reduction accounts for incomplete cross-tolerance, where a patient may be more sensitive to a new opioid than conversion tables predict. This safety step reduces the risk of overdose.

What defines an “opioid-tolerant” patient?

An opioid-tolerant patient is generally defined as someone who has been taking, for a week or longer, at least 60 mg of oral morphine per day, 30 mg of oral oxycodone per day, 8 mg of oral hydromorphone per day, or an equianalgesic dose of another opioid.

How long does a fentanyl patch take to work?

It can take 12 to 24 hours to reach therapeutic serum concentrations and achieve a significant analgesic effect. Breakthrough pain medication is essential during this induction period.

Can I use this tool to convert from methadone?

No. Methadone has a complex and highly variable equianalgesic ratio and a long, unpredictable half-life. Conversion from methadone requires specialist knowledge and should not be attempted with a standard calculator.

What is an Oral Morphine Equivalent (OME)?

OME is a standard measure used to compare the potencies of different opioids. It represents the dose of oral morphine that is considered equivalent in analgesic effect to a dose of another opioid.

Why doesn’t the calculator give a dose below 12 mcg/hr?

12 mcg/hr (sometimes labeled as 12.5 mcg/hr) is the lowest commercially available fentanyl patch strength. If the calculated dose is lower, a fentanyl patch may not be the appropriate therapy.

What should I do if the calculated dose is between two patch sizes?

Clinical judgment is required. It is generally safer to round down to the lower patch strength and supplement with short-acting opioids for breakthrough pain as needed, then titrate up at the next patch change if necessary.

How is the breakthrough dose calculated?

The recommended dose for breakthrough pain is typically 10-15% of the total 24-hour opioid dose. This calculator uses that range for conversions from fentanyl to a new opioid.

References

The conversion ratios and clinical principles used in this tool are based on established guidelines and prescribing information. Always consult the primary sources and exercise independent clinical judgment.

• 1. Dowell D, Ragan KR, Jones CM, Baldwin GT, Chou R. CDC Clinical Practice Guideline for Prescribing Opioids for Pain — United States, 2022. MMWR Recomm Rep 2022;71(No. RR-3):1–95. View Source
• 2. U.S. Food and Drug Administration (FDA). DURAGESIC® (fentanyl transdermal system) Prescribing Information. View PDF
• 3. The Palliative Care Network of Wisconsin. Fast Facts and Concepts #036: Opioid Conversion Ratios. View Source
• 4. Washington State Health Care Authority. Opioid Dose Calculator and Resources. View Source