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.

Oral Morphine to Fentanyl Patch Converter

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.