Converting from Short-Acting to Long-Acting Opioids

Introduction to Conversion

The National Comprehensive Cancer Network recommends calculating the total 24-hour opioid requirement of the current short-acting medication, then converting to an equianalgesic dose of the long-acting opioid, reducing the calculated dose by 25-50% to account for incomplete cross-tolerance 1, 2

To convert a patient from short-acting to long-acting opioids, calculate the total daily dose of the current short-acting opioid, which is the total amount of short-acting opioid taken in a 24-hour period that effectively controls pain 1, 2
Use equianalgesic conversion tables to determine the equivalent dose of the desired long-acting opioid, and for oral-to-oral conversions of common opioids, use standard conversion factors 1, 2
Reduce the calculated dose by 25-50% to account for incomplete cross-tolerance, unless pain was poorly controlled, in which case begin with 100% of the equianalgesic dose or increase by up to 25% 2, 5

When converting to extended-release oral morphine or oxycodone, calculate the total daily dose of the current short-acting opioid and convert to the equivalent daily dose of the long-acting formulation, then divide by 2 for twice-daily dosing 2
When converting to transdermal fentanyl, calculate the 24-hour analgesic requirement of the current opioid, convert to oral morphine equivalent if necessary, and select the appropriate fentanyl patch strength based on the conversion table 5, 4

Ensure pain is relatively well-controlled on short-acting opioid before initiating long-acting formulations, and use fentanyl patches only in opioid-tolerant patients 5
Monitor patients closely for respiratory depression, especially within the first 24-72 hours, and continue breakthrough medication once the long-acting dose is stabilized 3, 5
Avoid using codeine or morphine in patients with renal failure due to the risk of metabolite accumulation, and be aware that application of heat accelerates transdermal fentanyl absorption and should be avoided 5
Methadone conversions require special consideration due to its long and variable half-life, and significant variability exists in equianalgesic conversion calculations between different resources 3, 5