Morphine Equivalent Dose of 1800mcg IV Fentanyl
1800mcg of IV fentanyl is equivalent to 180mg of IV morphine, using the standard 1:100 conversion ratio for IV administration.
Conversion Calculation
The National Comprehensive Cancer Network establishes that the equianalgesic conversion ratio for IV fentanyl to IV morphine is 100:1 (100mcg IV fentanyl = 10mg IV morphine) 1
For 1800mcg IV fentanyl:
- 1800mcg ÷ 100 = 18 units
- 18 units × 10mg morphine = 180mg IV morphine equivalent 1
Critical Caveats About This Conversion
This 1:100 ratio applies ONLY to IV fentanyl compared with IV morphine - it does NOT apply to transdermal fentanyl, which uses entirely different conversion calculations 1
The National Comprehensive Cancer Network explicitly warns that "the equianalgesic dose listed only applies to IV fentanyl compared with other IV opioids" 1
Significant variability exists in clinical practice: A 2016 survey of 319 clinicians found that mean morphine equivalent doses for 1800mcg fentanyl ranged from 150-180mg, with standard deviations exceeding ±100mg, demonstrating substantial inconsistency in how clinicians perform these conversions 2
Age-Related Considerations
Fentanyl becomes relatively less clinically effective compared to morphine as patient age increases 3
In mechanically ventilated ICU patients, the fentanyl:morphine ratio was 1:93 in patients aged 18-29 years but decreased to 1:25 in patients ≥80 years old, meaning older patients required proportionally more fentanyl to achieve equivalent analgesia 3
For elderly patients (≥80 years), the 1:100 conversion may overestimate fentanyl's potency, potentially leading to inadequate analgesia if converting from fentanyl to morphine 3
Clinical Context for Opioid Rotation
When rotating opioids, if pain was well-controlled on the original opioid, reduce the calculated equianalgesic dose by 25-50% to account for incomplete cross-tolerance 1, 4
If pain was poorly controlled, you may use 100% of the equianalgesic dose or increase by 25% 1
Always provide breakthrough medication during opioid rotation, typically 10-20% of the total 24-hour dose as short-acting opioid 5, 4