#36

Calculating Opioid Dose Conversions

  • Robert Arnold MD
  • David E Weissman MD

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Introduction    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.   See Fast Fact #2 about conversions involving transdermal fentanyl; #75 and #86 about methadone; and #181 about oxymorphone. 

Caution:  Published values in equianalgesic tables should be considered a rough clinical guide when making dose conversions; substantial inter-individual variation exists.  The final prescribed dose needs to take into account a patients’ age, renal, pulmonary and hepatic function; their current pain level and opioid side effects such as sedation; as well as prior and current opioid 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 = Hydrocodone 30 mg oral = Oxycodone 20-30 mg oral (see Reference 1). 

A.  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

  1. Calculate the 24 hour current dose: 90mg q 12 = 180 mg Morphine/24 hours
  2. Use the oral to parenteral equianalgesic ratio: 30 mg PO Morphine = 10 mg IV Morphine
  3. Calculate new dose using ratios: 180/30 x 10 = 60 mg IV Morphine/24 hours or 2.5 mg/hour infusion
  4. Some experts recommend starting the new opioid at 75% of the calculated dose to account for inter-individual variation in first pass clearance.

B.  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, in the setting of well-controlled pain.

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 Morphine/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 0.5 = 22 mg/24 hours = 4 mg q4h

C. 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 Morphine/24 hrs
  2. Use the equianalgesic ratio of PO to IV morphine: 30 mg po Morphine = 10 mg IV Morphine
  3. Calculate new dose using ratios: 180/30 x 10 = 60 mg IV Morphine/24 hours
  4. Use the equianalgesic ratio of IV Morphine to IV Hydromorphone: 10 mg Morphine = 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 0.5 = 4.5 mg/24 hours = 0.2 mg IV continuous infusion
  7. Note: one would also get the same amount of hydromorphone if you directly converted from oral morphine to IV hydromorphone using the 30 mg :1.5 mg ratio

References:

  1. Gammaitoni AR, Fine P, Alvarez N, McPherson ML.  Clinical application of opioid equianalgesic data.  Clin J Pain. 2003; 19:286-297.
  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.

Version History:  This Fast Fact was originally edited by David E Weissman MD.  2nd Edition published July 2005; 3rd Edition May 2015. Re-copy-edited March 2009; references updated. Revised December 2012; hydrocodone and oxycodone added to the equianalgesic table using standard values; copy-edited again May 2015.