FENTANYL-87
Clinical safety rating: avoid
CNS depressants including alcohol and benzodiazepines increase sedation risk Life-threatening respiratory depression may occur.
Fentanyl is a synthetic opioid that primarily acts as a mu-opioid receptor agonist, inhibiting adenylate cyclase, decreasing cAMP production, and modulating ion channels (calcium, potassium) to reduce neurotransmitter release and neuronal excitability.
| Metabolism | Fentanyl undergoes extensive hepatic metabolism via CYP3A4-mediated N-dealkylation to norfentanyl, along with other minor pathways; elimination is primarily renal. |
| Excretion | Primarily hepatic metabolism (>90%) to norfentanyl and other inactive metabolites; renal excretion of metabolites accounts for approximately 75% of total elimination, with about 9% excreted unchanged in urine. Fecal excretion is minimal (<9%). |
| Half-life | Terminal elimination half-life is approximately 3–12 hours (mean 7 hours) in adults; prolonged to up to 20–30 hours in elderly, critically ill, or patients with hepatic impairment. Context-sensitive half-life increases with infusion duration. |
| Protein binding | Approximately 80–85% bound to plasma proteins (primarily alpha-1-acid glycoprotein and albumin). Increased free fraction in hypoalbuminemia. |
| Volume of Distribution | 4–6 L/kg (large, extensive tissue distribution). High Vd reflects rapid redistribution from blood to tissues (muscle, fat). |
| Bioavailability | Intravenous: 100%; intramuscular: ~90%; oral transmucosal: ~50% (range 25–70%, first-pass hepatic metabolism); intranasal: ~50–90%; transdermal: ~30–50% (variable, rate-limited by skin barrier). |
| Onset of Action | Intravenous: nearly immediate (30–60 seconds); intramuscular: 7–15 minutes; transdermal: delayed onset (~12–24 hours for initial effect, requires 24–72 hours for steady state); intranasal: 5–15 minutes; oral transmucosal: 5–15 minutes. |
| Duration of Action | Intravenous/Intramuscular: 30–60 minutes (analgesic effect); transdermal: 72 hours per patch (analgesic) but respiratory depression may persist longer; oral transmucosal: 1–2 hours. Duration is dose-dependent and affected by redistribution. |
| Molecular Weight | 336.47 |
IV: 0.5-2 mcg/kg as a bolus; continuous infusion: 0.7-10 mcg/kg/hr. Transdermal: 25-100 mcg/h every 72 hours. Transmucosal (buccal or lozenge): 200-1600 mcg as a single dose.
| Dosage form | FILM, EXTENDED RELEASE |
| Renal impairment | No specific dose adjustment required for GFR ≥30 mL/min. For GFR <30 mL/min, consider dose reduction by 50% or increase dosing interval. Caution in renal impairment due to potential accumulation of metabolites. |
| Liver impairment | Child-Pugh A: No adjustment. Child-Pugh B: Reduce dose by 50%. Child-Pugh C: Use with caution; consider 75% dose reduction. Monitor for prolonged effect. |
| Pediatric use | IV bolus: 1-2 mcg/kg for analgesia; for sedation/analgesia: 1-2 mcg/kg followed by infusion 0.5-2 mcg/kg/hr. Transdermal: Not recommended for opioid-naive pediatric patients. Transmucosal: Not recommended for children under 2 years. |
| Geriatric use | Reduce initial dose by 50% compared to younger adults. Titrate slowly; monitor for respiratory depression and constipation. Consider using lower strength transdermal patches (12 mcg/h or 25 mcg/h). |
| 1st trimester | Fentanyl crosses the placenta; limited human data but animal studies have shown adverse effects. Use only if clearly needed. |
| 2nd trimester | Use with caution; may cause respiratory depression in fetus if used near term. No known teratogenicity in first trimester use. |
| 3rd trimester | Use near term can cause neonatal respiratory depression, withdrawal syndrome, and altered placental perfusion. Avoid use during labor unless for acute pain management with resuscitation available. |
Clinical note
CNS depressants including alcohol and benzodiazepines increase sedation risk Life-threatening respiratory depression may occur.
| FDA category | Positive |
| Placental transfer | Rapidly crosses placenta; can achieve fetal/maternal ratios of 0.5-1.0. Transfer is dependent on protein binding and ionization. |
■ FDA Black Box Warning
Fentanyl carries a risk of respiratory depression, abuse, misuse, addiction, and diversion. Concomitant use with benzodiazepines or other CNS depressants may cause profound sedation, respiratory depression, coma, and death. Neonatal opioid withdrawal syndrome may occur with prolonged use during pregnancy.
| Common Effects | Constipation |
| Serious Effects |
Hypersensitivity to fentanyl or any formulation componentsAcute or severe bronchial asthma in unmonitored settingSignificant respiratory depressionConcurrent use of MAOIs or within 14 days of discontinuationKnown or suspected gastrointestinal obstruction (e.g., paralytic ileus)
| Precautions | Life-threatening respiratory depression; risk of serotonin syndrome with concurrent serotonergic drugs; adrenal insufficiency; severe hypotension; bradycardia; use in patients with head injuries or increased intracranial pressure; opioid-induced hyperalgesia; withdrawal if abruptly discontinued. |
Loading safety data…
| Breastfeeding |
| Fentanyl enters breast milk in low concentrations; peak levels occur after parenteral administration. Use with caution in breastfeeding, especially with repeated high doses or during lactation in opioid-tolerant mothers. Monitor infant for sedation and respiratory depression. |
| Lactation Rating | L3 - Moderately Safe |
| Teratogenic Risk | First trimester: Limited human data; animal studies show increased risk of neural tube defects at high doses. Second/third trimester: Chronic use may cause fetal opioid dependence and neonatal abstinence syndrome; avoid prolonged high-dose use. |
| Fetal Monitoring | Monitor maternal respiratory rate, oxygen saturation, and sedation level. For fetal monitoring, assess fetal heart rate during labor; watch for neonatal respiratory depression after delivery. |
| Fertility Effects | May impair fertility in both sexes by altering gamete function and hormonal regulation; data from opioid class suggest decreased libido and menstrual irregularities. |
| Food/Dietary |
| No significant food interactions have been reported. However, fentanyl should be taken on an empty stomach only when specified by the prescriber for transmucosal formulations. Grapefruit juice may theoretically increase fentanyl levels due to CYP3A4 inhibition, but clinical significance is minimal; avoid large amounts. |
| Clinical Pearls | Fentanyl is 50-100 times more potent than morphine. For opioid-naive patients, start with the lowest effective dose. Monitor for respiratory depression, especially during initiation and dose titration. Consider co-administration of naloxone for home use in patients at high risk for overdose (e.g., high doses, concurrent benzodiazepine use). Transdermal patches are contraindicated in acute pain due to slow onset. Do not heat or cut fentanyl patches. In patients with renal impairment, fentanyl is preferred over morphine due to lack of active metabolites that accumulate. |
| Patient Advice | Do not stop taking this medication abruptly; it may cause withdrawal symptoms. · Do not drive or operate heavy machinery until you know how fentanyl affects you. · Keep this medication in a safe place away from children and pets. · Do not consume alcohol or sedatives while taking fentanyl. · Seek emergency medical help if you have trouble breathing, excessive drowsiness, or fainting. · Do not apply heat (heating pad, hot tub) to the patch site as it may increase absorption. · Dispose of used patches by folding adhesive sides together and flushing down toilet. |