Clinical meaning
Opioid equianalgesic dosing compares the analgesic potency of different opioids to facilitate safe conversion between medications or routes while maintaining equivalent pain relief. The equianalgesic reference standard is morphine 10 mg IV or 30 mg oral. Key equivalences include: hydromorphone 1.5 mg IV = morphine 10 mg IV (hydromorphone is approximately 7 times more potent than oral morphine), oxycodone 20 mg oral ≈ morphine 30 mg oral, and hydrocodone 30 mg oral ≈ morphine 30 mg oral. When converting between opioids, a 25-50% dose reduction from the calculated equianalgesic dose is applied due to incomplete cross-tolerance between opioid receptor subtypes. Route conversion factors differ from drug equivalences: oral-to-IV morphine ratio is 3:1 (30 mg oral = 10 mg IV). Methadone and fentanyl have unique pharmacokinetics requiring special conversion tables and caution. Morphine milligram equivalents (MME) are used to assess total daily opioid exposure and overdose risk, with doses > 90 MME/day associated with significantly increased overdose risk.
Exam relevance
Risk factors: - Mathematical errors during opioid conversion calculations - Incomplete cross-tolerance between different opioid medications - Failure to reduce dose by 25-50% when switching opioids - Renal or hepatic impairment altering opioid metabolism - Concurrent CNS depressants potentiating respiratory depression