Hydromorphone to Morphine: how to convert safely

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Worked example

1. Total the 24-hour hydromorphone dose — say 8 mg/day oral.
2. Convert to morphine equivalents: 8 mg × 4 = 32 mg MME/day.
3. Convert to morphine: 32 ÷ 1 = 32 mg/day.
4. Apply a 25–50% cross-tolerance reduction: start near 24 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

• Hydromorphone is roughly 4–5× more potent than oral morphine mg-for-mg — dose-entry and unit errors with this drug are a recurring cause of serious opioid overdoses in hospitals.
• Preferred over morphine in renal impairment (no clinically significant active metabolite accumulation at usual doses), but still start low in dialysis patients.
• 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 8 mg of oral hydromorphone per day?

8 mg/day of oral hydromorphone is approximately 32 mg/day of oral morphine (8 mg × 4 MME factor ÷ 1 = 32 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 hydromorphone to morphine?

Oral hydromorphone has a morphine milligram equivalent (MME) factor of 4 and oral morphine a factor of 1, so 1 mg of hydromorphone ≈ 4 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 hydromorphone 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.