Opioid Equivalency and Conversion

Equianalgesic conversion places different opioids and routes on a common morphine scale so that analgesic exposure can be compared. The comparison is needed because opioids differ in mu-receptor potency, oral bioavailability, and the way active metabolites accumulate. The result is an estimate, not a chemically exact exchange. Conversion tables are derived from population averages, while an individual patient's response is shaped by age, frailty, prior opioid exposure, organ function, pain mechanism, and concurrent sedatives. Two patients with the same calculated morphine milligram equivalent (MME) may have very different analgesia or respiratory-depression risk. MME/day is therefore a risk-assessment and dose-comparison tool. It is not a direct prescription for the replacement opioid. A value of 60 MME/day does not mean that the patient can safely be switched to 60 mg of another opioid. Route matters separately from drug potency. A commonly taught estimate is 30 mg oral morphine ≈ 10 mg IV morphine, or an oral-to-IV ratio of about 3:1. This route relationship reflects first-pass metabolism and must not be confused with an oral-only MME factor.