Opioid conversion
Formal Definition
The process of converting a patient's opioid regimen from one agent or route to another using equianalgesic tables; requires calculating the morphine milligram equivalent (MME) of the current regimen, applying a conversion factor, and reducing the calculated dose by 25–50% to account for incomplete cross-tolerance when switching between opioid classes.
How It's Used on the Ward
"Convert to oral opioids" or "what is the opioid equivalent?" — the dose calculation required when transitioning from IV to PO, or from one opioid to another.
Example
""Patient on 4mg IV hydromorphone/day ready for oral transition: 4mg IV hydromorphone = 20mg oral hydromorphone OR approximately 60mg oral morphine equivalent. Converting to oxycodone ER 20mg q12h with oxycodone IR 5mg q4h PRN for breakthrough — reduced by 30% for incomplete cross-tolerance.""
Clinical Context
Equianalgesic conversions (approximate): oral morphine 30mg = IV morphine 10mg = oral oxycodone 20mg = oral hydromorphone 7.5mg = IV hydromorphone 1.5mg = transdermal fentanyl 12mcg/hr (for chronic use). Methadone: highly variable conversion (long half-life, risk of QT prolongation and accumulation) — always involve palliative care or pain specialist. Cross-tolerance reduction: when switching opioids, reduce calculated equivalent by 25–50% (tolerance does not fully transfer). Transdermal fentanyl: steady state takes 12–17 hours to establish, patch remains active 12–24 hours after removal — account for this when overlapping. Always prescribe a bowel regimen with any opioid.