FENTANYL-50
Clinical safety rating: avoid
CNS depressants including alcohol and benzodiazepines increase sedation risk Life-threatening respiratory depression may occur.
Fentanyl is a synthetic opioid agonist primarily acting on mu-opioid receptors in the central nervous system, leading to analgesia, sedation, and respiratory depression. It also interacts with kappa and delta receptors to a lesser extent.
| Metabolism | Primarily metabolized via CYP3A4 in the liver to norfentanyl (inactive) and other metabolites; minor contributions from CYP3A5. Less than 10% excreted unchanged in urine. |
| Excretion | Renal: 75% (primarily as metabolites, <10% unchanged); Fecal: 9%; Biliary: minor contribution. |
| Half-life | Terminal elimination half-life: 3-12 hours (mean 7 hours); context: prolonged with continuous infusion or in elderly, hepatic impairment, or obesity due to accumulation in adipose tissue. |
| Protein binding | 80-85% bound, primarily to alpha-1-acid glycoprotein and albumin. |
| Volume of Distribution | 3-8 L/kg (mean 4 L/kg); high Vd indicates extensive distribution into tissues including skeletal muscle and fat. |
| Bioavailability | IV: 100%; Transdermal: 92% (relative to IV, absolute bioavailability ~92%); Transmucosal (buccal, sublingual): 50-70%; Intranasal: 70-90%; Oral: low (<50% due to first-pass metabolism). |
| Onset of Action | IV: almost immediate (30-60 seconds); IM: 7-15 minutes; Transdermal: 12-18 hours (steady state achieved in 24-72 hours); Intranasal: 5-15 minutes. |
| Duration of Action | IV: 30-60 minutes (single dose); IM: 1-2 hours; Transdermal: 72 hours (patch removal continues analgesia for 12-24 hours due to dermal depot); Intranasal: 1-2 hours. |
| Molecular Weight | 336.47 |
50 mcg intravenously every 5-10 minutes as needed for breakthrough pain or for induction of anesthesia; for transdermal, 12-100 mcg/hour applied every 72 hours.
| Dosage form | FILM, EXTENDED RELEASE |
| Renal impairment | GFR 30-60 mL/min: reduce dose by 25-50%; GFR <30 mL/min: avoid or reduce dose by 50-75% and monitor closely. |
| Liver impairment | Child-Pugh class A: no adjustment; Child-Pugh class B: reduce dose by 50%; Child-Pugh class C: reduce dose by 75% or avoid use. |
| Pediatric use | Intravenous: 0.5-2 mcg/kg per dose every 5-10 minutes as needed; transdermal: not recommended for children under 2 years; for children >2 years, start at 12 mcg/hour based on prior opioid exposure. |
| Geriatric use | Starting dose should be 50-75% lower than in younger adults; titrate slowly; transdermal patch starting dose no higher than 25 mcg/hour; monitor for respiratory depression and cognitive impairment. |
| 1st trimester | Avoid unless maternal benefit outweighs risk. Not recommended for routine use. Human data limited; animal studies show teratogenic effects at high doses. Use only for anesthesia or opioid-dependent mothers. |
| 2nd trimester | Avoid unless maternal benefit outweighs risk. Associated with fetal growth restriction and preterm labor with chronic use. Use low-dose, short-term for procedures. |
| 3rd trimester | Avoid near term if possible. Risk of neonatal respiratory depression and withdrawal syndrome. Use only for maternal analgesia/anesthesia with careful monitoring. |
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. Fetal concentrations reach 50-100% of maternal levels. Transfer is determined by maternal dose, protein binding, and pH gradient. |
■ FDA Black Box Warning
Black Box Warning: Risk of respiratory depression, addiction, abuse, and misuse; life-threatening respiratory depression and death can occur at any dose, especially with initial use or dose escalation. Concomitant use with CNS depressants (e.g., benzodiazepines, alcohol) may cause profound sedation, respiratory depression, coma, and death. Accidental exposure (especially in children) can be fatal.
| Common Effects | Constipation |
| Serious Effects |
Hypersensitivity to fentanyl or any component of the productConcurrent use of MAOIs or within 14 days of discontinuationSevere respiratory insufficiency or depressionAcute or postoperative paralytic ileusSevere haemodynamic instability (e.g., hypovolaemia, severe hypotension)
| Precautions | Risk of respiratory depression requires monitoring; use with caution in COPD, decreased respiratory reserve, or hypoxia, Serotonin syndrome risk with concomitant serotonergic drugs, Adrenal insufficiency and androgen deficiency with prolonged use, Neonatal opioid withdrawal syndrome with prolonged maternal use during pregnancy, Severe hypotension, especially in hypovolemic patients, QT prolongation (high doses, especially IV), Risks of tolerance, physical dependence, and withdrawal upon abrupt discontinuation |
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| Breastfeeding | Fentanyl is excreted in low concentrations in breastmilk. After single doses, milk levels are minimal and considered compatible. With chronic high-dose use (e.g., patches), monitor infant for drowsiness, feeding difficulties, and weight gain. Use lowest effective dose for shortest duration. |
| Lactation Rating | L2 (Safe – compatible with breastfeeding for single doses; caution with chronic use) |
| Teratogenic Risk | First trimester: Limited data, but animal studies show no structural teratogenicity at clinically relevant doses. Second/third trimester: Chronic exposure may cause neonatal opioid withdrawal syndrome (NOWS) and respiratory depression at delivery. Avoid prolonged use. |
| Fetal Monitoring | Maternal: heart rate, blood pressure, respiratory rate, oxygen saturation, sedation level. Fetal: heart rate monitoring (especially during labor), growth ultrasound if prolonged use, neonatal monitoring for withdrawal after delivery. |
| Fertility Effects | Animal studies show no impairment of fertility at therapeutic doses. In humans, chronic opioid use may disrupt menstrual cycles and reduce libido due to hormonal changes (e.g., hypothalamic-pituitary-gonadal axis suppression). Reversible upon discontinuation. |
| Food/Dietary | Avoid alcohol; concurrent use increases risk of CNS depression and respiratory arrest. No specific food interactions; maintain usual diet. Grapefruit juice may slightly increase fentanyl levels via CYP3A4 inhibition but clinical significance is minimal with transdermal route. |
| Clinical Pearls | Fentanyl 50 mcg/hr patch provides continuous systemic opioid delivery. Onset of action 12-24 hours; steady state in 72 hours. Do not cut or use damaged patches. Avoid heat sources (fever, heating pads, saunas) as they increase absorption and risk of overdose. Monitor for respiratory depression, especially in opioid-naïve patients. C max may increase by 25-40% with fever. Apply to non-irritated, non-hairy skin on upper torso. Use in opioid-tolerant patients only. |
| Patient Advice | Apply patch to clean, dry, hairless skin on chest or back, avoiding scars, lesions, or irritated skin. · Do not cut, tear, or alter the patch in any way; this can cause rapid, fatal drug absorption. · Wash hands after applying or removing patch; avoid touching eyes or mucous membranes. · Keep away from children and pets; used patches should be folded, placed in original packaging, and disposed of per local drug take-back programs. · Avoid hot tubs, saunas, electric blankets, heating pads, or prolonged sun exposure while wearing patch; fever can increase absorption. · Do not drink alcohol while using fentanyl; it can cause severe drowsiness, respiratory depression, and death. · Common side effects include nausea, constipation, drowsiness, and dizziness. Contact healthcare provider if you experience confusion, slow or shallow breathing, or severe sedation. |