Fast Fact and Concept #036: Calculating Opioid Dose Conversions

2nd Edition

Author(s): Robert Arnold, MD and David E. Weissman, MD

A variety of published conversion tables exist to provide clinicians a rough guide for making calculations when switching between different opioid routes or preparations. Listed below are methods for common conversions using standard published conversion ratios. The examples assume a change in drug or route at a time of stable pain control using equianalgesic doses.

Note: Published values in equianalgesic tables should be considered a rough clinical guide when making dose conversions. The final prescribed dose needs to take into account a patients’ age, renal, pulmonary and hepatic function, along with prior opioid past and current use.

Opioid Equianalgesic Conversion Ratios for use with the following examples ** Morphine 10 mg parenteral = Morphine 30 mg oral = Hydromorphone 1.5 mg parenteral = Hydromorphone 7.5 mg oral (American Pain Society)

1. Change route, keeping drug the same (e.g. oral to IV morphine)
   Example: Change 90 mg q12 Extended Release Morphine to Morphine by IV continuous infusion
   • Calculate the 24 hour current dose: 90mg q 12 = 180 mg MS/24 hours
   • Use the oral to parenteral equianalgesic ratio: 30 mg po MS = 10 mg IV MS
   • Calculate new dose using ratios: 180/30 x 10 = 60 mg IV MS/24 hours or 2.5 mg/hour infusion
   • Some experts recommend starting the new opioid at 75% of the calculated dose to account for inter-individual variation in first pass clearance.
     
2. Change drug, keep the same route: (e.g. po morphine to po hydromorphone)
   There is incomplete cross-tolerance between different opioids, but the exact amount will differ, thus, equianalgesic tables are only approximations. Depending on age and prior side effects, most experts recommend starting a new opioid at 50% of the calculated equianalgesic dose.
   Example: Change 90 mg q 12 Extended Release Morphine to oral hydromorphone
   1. Calculate the 24 hour current dose: 90 Q12 x 2 = 180 mg po MS/24 hrs
   2. Use the equianalgesic ratio: 30 mg po morphine = 7.5 mg po hydromorphone
   3. Calculate new dose using ratios: 180/30 X 7.5 = 45 mg oral hydromorphone/24 hours.
   4. Reduce dose 50% for cross-tolerance: 45 x.5 = 22 mg/24 hours = 4 mg q4h
      
3. Changing drug and route (e.g. oral morphine to IV hydromorphone)
   Example: Change from 90 mg q12 Extended Release Morphine to IV hydromorphone as a continuous infusion
   1. Calculate the 24 hour current dose: 90 Q12 x 2 = 180 mg po MS/24 hrs
   2. Use the equianalgesic ratio of po to IV morphine: 30 mg po MS = 10 mg IV MS
   3. Calculate new dose using ratios: 180/30 x 10 = 60 mg IV MS/24 hours
   4. Use the equianalgesic ratio of IV morphine to IV hydromorphone: 10 mg MS = 1.5 mg hydromorphone
   5. Calculate new dose using ratios: 60/10 x 1.5 = 9 mg IV hydromorphone/24 hours
   6. Reduce dose 50% for cross-tolerance: 9 x.5 = 4.5 mg/24 hours = 0.2 mg IV continuous infusion

See Fast Fact #2 for fentanyl transdermal dose conversions. See Fast Fact #75 and #86 for methadone conversions.

References:

1. Principles of analgesic use in the treatment of acute pain and cancer pain. American Pain Society, 5 th Edition, 2003 www.ampainsoc.org
2. Pereira J et al. Equianalgesic dose rations for opioids: a critical review and proposals for long-term dosing. J Pain Sym Manage 2001;22:672-687.
3. Anderson R et al. Accuracy in equianalgesic dosing: conversion dilemmas. J Pain Sym Manage 2001; 21:397-406.

Fast Facts were edited by David Weissman MD, Palliative Care Center, Medical College of Wisconsin until January 2007.  For comments/questions write to the current editor, Drew Rosielle MD: drosiell@mcw.edu. The complete set of Fast Facts is available at EPERC: www.eperc.mcw.edu

Copyright/Referencing Information : Users are free to download and distribute Fast Facts for educational purposes only. Citation for referencing: Arnold R and Weissman DE . Calculating Opioid Dose Conversions. Fast Fact and Concept #38; 2nd Edition, July 2005. End-of-Life Palliative Education Resource Center www.eperc.mcw.edu .

Disclaimer: Fast Facts provide educational information, this information is not medical advice. Health care providers should exercise their own independent clinical judgment. Some Fast Fact information cites the use of a product in dosage, for an indication, or in a manner other than that recommended in the product labeling. Accordingly, the official prescribing information should be consulted before any such product is used.

Creation Date: 3/2001; 2nd Edition, July 2005.
Purpose: Instructional Aid, Self-Study Guide, Teaching
Audience(s)

• Training: Fellows, 3rd/4th Year Medical Students, PGY1 (Interns), PGY2-6, Physicians in Practice
• Specialty: Anesthesiology, Emergency Medicine, Family Medicine, General Internal Medicine, Geriatrics, Hematology/Oncology, Neurology, OB/GYN, Ophthalmology, Pulmonary/Critical Care, Pediatrics, Psychiatry, Surgery
• Non-Physician: Nurses

ACGME Competencies: Medical Knowledge
Keyword(s): Pain>opioids