Morphine to Hydromorphone: how to convert safely
Bottom line
1 mg oral morphine ≈ 0.3 mg oral hydromorphone (MME factors 1 → 4). After converting, reduce the calculated dose by 25–50% for incomplete cross-tolerance and re-titrate to effect.
Worked example
- Total the 24-hour morphine dose — say 30 mg/day oral.
- Convert to morphine equivalents: 30 mg × 1 = 30 mg MME/day.
- Convert to hydromorphone: 30 ÷ 4 = 7.5 mg/day.
- Apply a 25–50% cross-tolerance reduction: start near 5.6 mg/day or lower, divided by the dosing interval, with breakthrough doses available.
Try it with your patient's numbers
01 · From
Current regimen
Normalized: 30.0 MME/day
24-hour MME bridge30.0MME/day→↓
02 · To
Target regimen
Incomplete cross-tolerance reduction
03 · Estimated starting pointNo reduction applied
Hydromorphone 7.5 mg PO/day
30.0 mg/dayMorphine (PO)× 130.0 MMEnormalized÷ 47.5 mg/dayequianalgesic− 0%7.5 mg/daystarting estimate
Show calculation detail
1) Start: Morphine 30.0 mg PO/day
2) Convert to morphine equivalent: 30.0 mg × 1 → 30.0 mg MED/day
3) Convert to Hydromorphone (PO): 30.0 ÷ 4 → 7.5 mg/day
4) Cross-tolerance: 0%
→ Final conversion= 7.5 mg/day
!
Starting estimate, not a prescription. Round conservatively and reassess pain, sedation, organ function, interactions, and clinical trajectory before ordering.
Cautions specific to this switch
- 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.
- 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.
- 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 hydromorphone equals 30 mg of oral morphine per day?
- 30 mg/day of oral morphine is approximately 7.5 mg/day of oral hydromorphone (30 mg × 1 MME factor ÷ 4 = 7.5 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 morphine to hydromorphone?
- Oral morphine has a morphine milligram equivalent (MME) factor of 1 and oral hydromorphone a factor of 4, so 1 mg of morphine ≈ 0.3 mg of hydromorphone. 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 morphine to hydromorphone, 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.
Creado y mantenido por Yasmine Abbey, MD, MSc · Última revisión:
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