PRN Opioid Dose Calculation Guide

⚠️ Clinical Disclaimer: This explains PRN opioid calculations. Always use clinical judgment, consider patient factors, and follow institutional protocols.

1 Calculate Total Daily Oral Morphine Equivalent Dose (oMED)

Convert all opioids used in last 24hrs (regular + additional/PRN) to PO morphine equivalents.

Total oMED = Σ (Each Opioid Dose × Conversion Ratio)

2 Define PRN oMED Range

Establish minimum and maximum PRN oMED based on total daily oMED:

PRN oMED Range = PRN oMED_min to PRN oMED_max

PRN oMED_min = oMED_total 12

PRN oMED_max = oMED_total 6

3 Calculate PRN Opioid Dose Range

Convert the PRN oMED range to the desired opioid by dividing each boundary by the PRN opioid ratio:

PRN Opioid Range = PRN oMED_min PRN Opioid Ratio to PRN oMED_max PRN Opioid Ratio

Worked Example

Example inputs:

Patient: Fentanyl patch 50mcg/hr + 30mg SC Morphine (last 24hrs)

Step 1 – Total oMED:
Fentanyl patch: 50mcg/hr × 24hrs × 2.4 = 120mg PO morphine
SC Morphine: 30mg × 2 = 60mg PO morphine
Total = 180mg PO morphine oMED

Step 2 – PRN oMED Range:
PRN min = 180/12 = 15mg
PRN max = 180/6 = 30mg
PRN Range: 15-30mg oMED

Step 3 – Convert to PRN PO Oxycodone (ratio = 1.5):
SC Oxy min = 15/1.5 = 10mg
SC Oxy max = 30/1.5 = 20mg
Final PRN: 10-20mg PO Oxycodone

Clinical Warnings

⚠️ Key Considerations:

TD patches(continuous delivery) cannot be used as PRN
PRN = breakthrough pain only
Adjust for patient response/tolerance
Monitor efficacy + side effects
Don't include incidental PRNs in total oMED

Math Formulas Summary

PRN oMED_min = oMED_total12

PRN oMED_max = oMED_total6

Target Opioid PRN Range = PRN oMED_minR_target to PRN oMED_maxR_target

R_target = conversion ratio to target opioid/route