Fentanyl conversion and pharmacology
A highly potent synthetic opioid (approx. 50-100 times morphine), used for severe pain, anesthesia, and breakthrough cancer pain.
Equianalgesic estimate
0.1mg (100mcg) Parenteral ≈ 10mg Parenteral Morphine
Published equianalgesic ratios vary between references and with clinical context. Read how to interpret conversion results before applying an estimate.
Mechanism of action
Potent mu-opioid receptor agonist.
Brand names: Duragesic, Sublimaze, Actiq, Fentora, Lazanda
Pharmacokinetics
- Protein binding
- 80-85%
- Volume of distribution
- 3-8 L/kg
- Half-life
- 3-7 hours (IV elimination); ~17 hours (after transdermal patch removal due to skin depot).
| Route | Form | Bioavailability | Onset | Peak | Duration |
|---|---|---|---|---|---|
| Parenteral | IV | — | Almost immediate | 3-5 min | 30-60 min (short due to rapid redistribution) |
| Transdermal | TD | — | 6-12 hours | 12-24 hours | 72 hours (steady state) |
| Transmucosal | — | 50-76% | 5-15 min | 20-40 min | 1-2 hours |
Metabolism
- CYP3A4 (N-dealkylation)
Metabolites
- Norfentanyl Inactive.
Highly lipophilic. Major CYP3A4 substrate. Potent CYP3A4 inhibitors (e.g., ritonavir, ketoconazole) drastically increase fentanyl levels (high risk of overdose).
Renal and hepatic impairment
Renal
Considered one of the safer opioids in renal failure as metabolites are inactive. Not significantly dialyzable.
Hepatic
Metabolism dependent on hepatic blood flow and CYP3A4; clearance may be reduced.
Clinical cautions
- Dosed in micrograms (mcg) due to extreme potency.
- Transdermal patch absorption is increased by heat (fever, heating pads), potentially causing overdose.
- Rapid IV administration can cause chest wall rigidity (Wooden Chest Syndrome).
- Transdermal fentanyl should not be used in opioid-naive patients.
For qualified healthcare professionals. This page is an educational reference, not prescribing advice. Check medicine information and conversion factors against a current clinical source and local guidance.
Other opioids in this reference
Convert fentanyl doses in the app
Calculate OME and compare opioid regimens on iOS and Android.
Last updated 30 August 2026. Read how to interpret conversion results and the Terms of Service.