Morphine to Fentanyl Equianalgesic Conversion

Route-Specific Conversion Ratios

When converting from IV fentanyl continuous infusion to transdermal fentanyl, use a 1:1 conversion ratio (the basal rate in mcg/hr equals the patch dose in mcg/hr) 1, 2
For opioid-naïve patients, 2-5 mg IV morphine is equivalent to approximately 25-50 mcg IV fentanyl 1, 2

Transdermal fentanyl should ONLY be used in opioid-tolerant patients with stable, controlled pain—never for rapid titration or in opioid-naïve patients 1, 2

Fentanyl is the preferred choice for patients with poor morphine tolerance, renal insufficiency, or severe constipation 1, 2, 3
Morphine-6-glucuronide accumulates in renal insufficiency causing neurotoxicity, making fentanyl safer in this population 1, 2, 3
Meta-analyses show fentanyl causes significantly less constipation, nausea, vomiting, drowsiness, and urinary retention compared to oral morphine 1, 2

Always reduce the calculated equianalgesic dose by 25-50% when switching between opioids to account for incomplete cross-tolerance 3

The National Comprehensive Cancer Network recommends starting with standard IV dosing (2-5 mg morphine equivalent = 25-50 mcg IV fentanyl) for opioid-naïve patients, regardless of genotype 4
The National Comprehensive Cancer Network suggests reducing the initial dose by 25-30% if CYP3A41G/1G or compound CYP3A41G + CYP3A53 variants are known, and titrating liberally based on clinical response rather than genotype alone 5
IV formulations have less significant drug interactions than oral formulations due to the absence of first-pass metabolism, as noted by the National Comprehensive Cancer Network 6, 7, 8
Fentanyl IV is the safest opioid choice in patients with chronic kidney disease stages 4-5 (eGFR <30 ml/min), regardless of CYP genotype, according to the Annals of Oncology 9
The National Comprehensive Cancer Network advises against using transdermal fentanyl for rapid titration or in opioid-naïve patients, and recommends avoiding morphine or hydromorphone in renal failure patients, instead switching to fentanyl 4, 5