Oxycodone to Morphine: how to convert safely

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Worked example

1. Total the 24-hour oxycodone dose — say 20 mg/day oral.
2. Convert to morphine equivalents: 20 mg × 1.5 = 30 mg MME/day.
3. Convert to morphine: 30 ÷ 1 = 30 mg/day.
4. Apply a 25–50% cross-tolerance reduction: start near 22.5 mg/day or lower, divided by the dosing interval, with breakthrough doses available.

Try it with your patient's numbers

Cautions specific to this switch

• Oxycodone is metabolized by CYP3A4 and CYP2D6 — strong CYP3A4 inhibitors (azoles, clarithromycin, some antivirals) can raise levels substantially.
• No parenteral form is available in the US; if the patient will lose enteral access, plan the rotation to an IV-capable agent before it happens.
• Active metabolites (M3G/M6G) accumulate in renal impairment — avoid or dose-reduce morphine when eGFR is reduced, and consider an alternative agent in dialysis patients.
• Histamine release can cause pruritus and hypotension, which is not a true allergy but is often documented as one.
• Equianalgesic tables are population averages. Re-assess pain, sedation (e.g. POSS), and respiratory status within hours of the first converted dose, not days.

Frequently asked questions

How much morphine equals 20 mg of oral oxycodone per day?

20 mg/day of oral oxycodone is approximately 30 mg/day of oral morphine (20 mg × 1.5 MME factor ÷ 1 = 30 mg), before any cross-tolerance reduction. Most patients switching opioids should start 25–50% below the calculated equianalgesic dose.

What is the conversion factor from oxycodone to morphine?

Oral oxycodone has a morphine milligram equivalent (MME) factor of 1.5 and oral morphine a factor of 1, so 1 mg of oxycodone ≈ 1.5 mg of morphine. Equianalgesic tables are population averages — individual response varies, so titrate to effect.

Why reduce the dose for incomplete cross-tolerance?

Tolerance to one opioid does not fully transfer to another. When rotating from oxycodone to morphine, standard practice is to reduce the calculated equianalgesic dose by 25–50% and provide breakthrough doses while re-titrating. Frail or elderly patients warrant the larger reduction.

Is this conversion exact?

No. Published equianalgesic factors are averages with wide interpatient variability, and they differ slightly between references. Treat the calculated dose as a starting estimate, apply a cross-tolerance reduction, and reassess pain and sedation frequently after the switch.