What conversion ratio does this use?

It uses the common palliative care banded approach where roughly every 30 to 60 mg of oral morphine over 24 hours corresponds to one step on the fentanyl patch scale. A widely cited approximation is that the patch mcg/hr is about half the daily oral morphine in mg divided by twelve, rounded to the nearest available patch.

Is conversion to fentanyl bidirectional and exact?

No. Opioid conversion is not perfectly reversible and there is significant interpatient variation. Conversions are deliberately conservative, and the new opioid is often started 25 to 50 percent lower to account for incomplete cross-tolerance.

How long until the patch reaches steady state?

Transdermal fentanyl takes 12 to 24 hours to reach useful plasma levels and up to 72 hours for steady state. Continue the previous analgesia cover during the first 12 hours and ensure breakthrough medication is available.

What breakthrough dose should I provide?

Breakthrough is usually one sixth of the total 24-hour oral morphine equivalent, given as an immediate-release opioid. The tool shows this estimate, which should be titrated to the individual patient.

What is the Oral Morphine to Fentanyl Patch Converter?

Converts a total daily oral morphine dose to the nearest transdermal fentanyl patch strength from 12 to 200 mcg/hr using published palliative care conversion bands. A reference aid for palliative care physicians and specialist nurses. It runs free in your browser on Gera Tools, with nothing uploaded.

Oral Morphine to Fentanyl Patch Converter

Name: Oral Morphine to Fentanyl Patch Converter
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

Oral morphine to transdermal fentanyl

Switching a patient from oral morphine to a transdermal fentanyl patch is a common step in palliative care when the oral route becomes unreliable or when a steadier analgesic level is needed. Because fentanyl is far more potent than morphine, conversion uses published banded tables rather than a single multiplier. This tool maps a total daily oral morphine dose to the nearest available patch strength.

How it works

The total 24-hour oral morphine dose (background plus breakthrough) is matched to a fentanyl patch band. A widely used approximation is:

patch (mcg/hr) approx = (daily oral morphine mg / 2) / 12

which is then rounded down to the nearest manufactured patch strength: 12, 25, 37, 50, 62, 75, 87, 100, 125, 150, 175, or 200 mcg/hr. The breakthrough dose is estimated as one sixth of the daily oral morphine equivalent.

Tips and cautions

Always round conservatively and consider starting 25 to 50 percent lower for incomplete cross-tolerance, especially in frail or opioid-sensitive patients. The patch takes 12 to 24 hours to take effect, so maintain prior cover and provide breakthrough analgesia. These bands are a reference aid; confirm against your local palliative care formulary and reassess frequently.

Clinical context: why patches are used in palliative care

Transdermal fentanyl patches are chosen over oral morphine when:

The oral route is no longer reliable — nausea, vomiting, dysphagia, or impaired absorption
A steady-state analgesic level is preferred to avoid peaks and troughs from four-hourly oral dosing
Compliance is a concern and a three-day depot is preferable to multiple daily tablets
The patient prefers fewer tablets or has difficulty managing a complex oral regimen

Fentanyl patches are not appropriate for patients with rapidly changing analgesic needs, for opioid-naive patients (high risk of toxicity), or in settings where rapid titration is required.

Understanding the pharmacokinetics

Transdermal fentanyl has a distinctive pharmacokinetic profile that differs from oral opioids:

Onset: Plasma levels begin rising within 1–2 hours of application, but meaningful analgesia takes 12–24 hours to develop as drug accumulates in the subcutaneous depot.
Steady state: Full steady-state plasma levels are reached after the second or third patch change (i.e., after 3–6 days on the same patch strength).
Duration: Each patch delivers medication for 72 hours (3 days). Some patients with high skin blood flow may need patch changes at 48 hours.
Offset after removal: Because of the subcutaneous depot, plasma fentanyl levels decline slowly after patch removal — serum levels drop by roughly 50% over the following 17–27 hours. This is important to know in cases of toxicity.

Managing the transition period

When switching from oral morphine to a fentanyl patch, the first 12–24 hours require careful management:

Apply the patch and continue oral morphine for the first 12 hours at the same or reduced dose while the patch builds up
After 12 hours, discontinue regular oral morphine but keep immediate-release morphine available as breakthrough
Breakthrough analgesia is usually one-sixth of the 24-hour oral morphine dose, provided as immediate-release morphine or an alternative short-acting opioid
Reassess at 72 hours (first patch change) and adjust the patch strength based on breakthrough requirements — frequent breakthrough use suggests the patch strength is insufficient

A note on this tool’s limitations

This reference uses banded conversion tables that are widely cited in palliative care formularies. However:

Conversion ratios in the literature vary; different formularies cite slightly different bands
Individual patients show significant variation in opioid sensitivity due to genetics, organ function, and prior opioid exposure
The tool does not account for renal or hepatic impairment, which affects fentanyl clearance
It is not validated for paediatric dosing

This is a clinical reference aid for use by qualified prescribers and specialist nurses. It does not replace local formulary guidelines, institutional protocols, or specialist palliative care advice.