Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ALFENTANIL vs GENGRAF
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Alfentanil is a potent, short-acting synthetic opioid analgesic that primarily acts as a mu-opioid receptor agonist. It binds to mu-opioid receptors in the central nervous system, leading to G-protein coupled activation of inwardly rectifying potassium channels and inhibition of voltage-gated calcium channels, resulting in hyperpolarization and reduced neurotransmitter release. This produces analgesia, sedation, and respiratory depression.
Calcineurin inhibitor; binds to cyclophilin, inhibits calcineurin-dependent T-cell activation, preventing nuclear factor of activated T-cells (NF-AT) dephosphorylation and translocation, thereby reducing IL-2 and other cytokine gene transcription.
Analgesic adjunct during general anesthesia,Induction of anesthesia,Maintenance of anesthesia for short surgical procedures,Off-label: Procedural sedation in monitored settings
Prophylaxis of organ rejection in kidney, liver, and heart allogeneic transplants,Treatment of active rheumatoid arthritis (FDA-approved for moderate to severe),Treatment of psoriasis (FDA-approved for severe, recalcitrant cases),Off-label: nephrotic syndrome, aplastic anemia, ulcerative colitis, atopic dermatitis
Initial IV bolus of 5-20 mcg/kg; maintenance infusion of 0.5-1.5 mcg/kg/min; incremental boluses of 5-10 mcg/kg as needed. Induction of anesthesia: 50-100 mcg/kg IV.
5-15 mg/kg/day orally in divided doses every 12 hours.
Terminal elimination half-life: 90–111 minutes (1.5–1.85 hours). Clinically, context-sensitive half-time is short (~40 min after 3-hour infusion) due to rapid redistribution and metabolism.
Terminal half-life is approximately 8.4 hours (range 5-18 hours) in adult volunteers; prolonged in hepatic impairment.
Alfentanil is primarily metabolized by hepatic cytochrome P450 enzymes, mainly CYP3A4, through oxidative N-dealkylation and O-demethylation to inactive metabolites.
Hepatic metabolism primarily via CYP3A4 enzyme; also substrate for CYP3A5. Metabolized to multiple metabolites with variable activity, including AM1 (hydroxylated), AM9 (N-demethylated), and AM4N (cyclized). Undergoes extensive first-pass metabolism.
Primarily hepatic metabolism via CYP3A4; <1% excreted unchanged in urine; metabolites (mainly noralfentanil) excreted renally. Biliary/fecal excretion of metabolites accounts for ~30%.
Primarily biliary/fecal (94%); renal excretion accounts for 6% (0.1% unchanged).
~92% bound primarily to alpha-1-acid glycoprotein (AAG) and albumin.
90-98% bound to plasma proteins, primarily lipoproteins, albumin, and alpha-1-acid glycoprotein.
Vd: 0.4–1.0 L/kg (mean ~0.75 L/kg). Moderate Vd reflecting rapid distribution to tissues, especially brain and muscle.
3.5 L/kg (range 1.2-4.8 L/kg) in renal transplant recipients; distribution is extensive and variable.
IV: 100%. IM: ~90%. Epidural: ~30–50% due to local uptake and redistribution. No significant oral bioavailability.
Oral bioavailability is 30% (range 10-60%), variable due to first-pass metabolism and food effects.
GFR 10-50 m L/min: administer with caution, consider dose reduction of 25-50%; GFR <10 m L/min: reduce dose by 50% and extend dosing interval.
GFR <30 m L/min: reduce dose by 50%.
Child-Pugh class A: no adjustment needed; Child-Pugh class B: reduce dose by 50%; Child-Pugh class C: reduce dose by 75%.
Child-Pugh Class A: no adjustment; Class B: reduce dose by 50%; Class C: avoid use.
Initial IV bolus of 5-20 mcg/kg; maintenance infusion of 0.5-2 mcg/kg/min. For neonates, reduce dose by 30-50% due to immature clearance.
4-10 mg/kg/day orally in divided doses every 12 hours; adjusted to target trough levels.
Reduce initial IV bolus by 30-50% to 3-10 mcg/kg; titrate carefully; monitor for prolonged sedation and respiratory depression.
Initiate at lower end of dosing range and titrate based on renal function and drug levels.
Risk of respiratory depression: Alfentanil can cause severe, life-threatening, or fatal respiratory depression. Monitor for respiratory depression, especially during initiation or following dose increases. Accidental ingestion of even one dose can be fatal. Concomitant use with central nervous system depressants (e.g., benzodiazepines, alcohol) may increase risk. Alfentanil is an opioid agonist and a Schedule II controlled substance with high potential for abuse and addiction.
Increased susceptibility to infection and development of lymphoma and other malignancies, particularly of the skin. Only physicians experienced in immunosuppressive therapy and management of transplant patients should prescribe cyclosporine.
Respiratory depression: Potentially fatal; monitor oxygenation and ventilation.,Abuse potential: Schedule II controlled substance; risk of addiction, abuse, and diversion.,Concomitant use with CNS depressants: Increases risk of profound sedation, respiratory depression, coma, and death; limit use or monitor closely.,Geriatric and cachectic patients: Increased sensitivity; reduce initial dose.,Hepatic impairment: Alfentanil clearance is reduced in patients with cirrhosis; consider dose adjustment.,Bradycardia and hypotension: Use with caution in patients with hypovolemia or reduced cardiac reserve.,Serotonin syndrome: Risk with concurrent serotonergic drugs (e.g., MAOIs, SSRIs, triptans); monitor for symptoms.,Withdrawal: Prolonged use may lead to physical dependence; taper dose gradually.
Nephrotoxicity: Monitor renal function regularly; risk increased with high doses, other nephrotoxic drugs, or prolonged use.,Hepatotoxicity: Monitor liver function.,Hypertension: Common; require blood pressure control.,Neurotoxicity: Including tremor, convulsions, headache, and paresthesias.,Hyperkalemia: Monitor serum potassium, especially with potassium-sparing diuretics or ACE inhibitors.,Hypomagnesemia: Supplementation may be required.,Increased risk of infections and lymphoproliferative disorders.,Potential for anaphylactic reactions with IV formulation (due to Cremophor EL).,Carcinogenesis: Especially skin malignancies; minimize UV exposure.
Hypersensitivity to alfentanil, fentanyl, or any opioid,Significant respiratory depression (e.g., acute asthma, COPD in acute exacerbation),Acute or severe bronchial asthma,Suspected or known paralytic ileus,MAO inhibitor use within 14 days (serotonin syndrome risk),Myasthenia gravis (relative contraindication due to risk of respiratory muscle weakness),Morbid obesity with sleep apnea (relative contraindication; increased risk of respiratory depression)
Hypersensitivity to cyclosporine or any component of the formulation (including Cremophor EL for IV),Uncontrolled hypertension,Malignancy (except non-melanoma skin cancer) in patients with rheumatoid arthritis or psoriasis,Concomitant use with PUVA or UVB therapy, methotrexate, other immunosuppressive agents, or coal tar (for psoriasis patients),Abnormal renal function with uncontrolled hypertension (for psoriasis patients),Pregnancy (category C; additional risk of premature birth and low birth weight)
No significant food interactions known. Avoid grapefruit and grapefruit juice as they may inhibit CYP3A4 metabolism, potentially prolonging effects.
Grapefruit and grapefruit juice increase cyclosporine levels and must be avoided. High-potassium foods (e.g., bananas, oranges, potatoes) may increase hyperkalemia risk; monitor intake. Avoid St. John's wort as it reduces drug levels.
Alfentanil is an opioid analgesic; limited human data. No clear evidence of major malformations, but third trimester use may cause neonatal opioid withdrawal syndrome (NOWS). Avoid prolonged use or high doses near term; use during labor may cause respiratory depression in neonate.
First trimester: Cyclosporine crosses the placenta. Limited human data, but no major malformations attributed. Second and third trimesters: Risk of intrauterine growth restriction, prematurity, and low birth weight. Consider risk-benefit; avoid if possible, but may be used if essential.
Alfentanil is excreted into breast milk in very low concentrations; estimated relative infant dose is low (<2% of maternal weight-adjusted dose). M/P ratio not determined in humans. Compatible with breastfeeding with caution; monitor infant for drowsiness, feeding difficulties.
Cyclosporine is excreted into breast milk. Milk-to-plasma ratio approximately 0.3-0.6. Potential for infant immunosuppression and growth inhibition. Weigh benefits against risks; monitor infant for adverse effects.
Pregnancy can alter alfentanil pharmacokinetics: increased volume of distribution, decreased plasma clearance, prolonged elimination half-life. Dose reduction may be needed for prolonged use; titrate to effect. During labor, use smallest effective dose.
Pregnancy reduces cyclosporine oral bioavailability and increases clearance; dose may need to be increased by 20-50% to maintain therapeutic trough levels. Frequent level monitoring recommended, especially in third trimester. Postpartum dose reduction likely needed.
Alfentanil is a potent, short-acting synthetic opioid (4-5 times more potent than fentanyl) with rapid onset (1-2 min) and brief duration (5-10 min). Primarily used for induction and maintenance of anesthesia, especially in short procedures. Requires careful monitoring of respiratory depression and chest wall rigidity, particularly during rapid IV administration. Hepatic metabolism (CYP3A4) affected by liver disease; reduce dose. Decrease dose in elderly and hypovolemic patients. Not recommended for chronic pain due to short half-life.
Monitor trough levels (target 100-400 ng/m L) and renal function closely. Calcineurin inhibitors cause nephrotoxicity; dose reduction may be necessary. Avoid use with potassium-sparing diuretics or ACE inhibitors due to hyperkalemia risk. Grapefruit increases levels; avoid coadministration. Remember to adjust dose for hepatic impairment.
This medication causes drowsiness and dizziness; avoid driving or operating machinery for at least 24 hours after administration.,Report any difficulty breathing, chest tightness, or feeling faint immediately.,Alfentanil is used only in hospital settings under direct supervision of healthcare professionals.,Inform your doctor if you have a history of liver disease, lung disease, or drug/alcohol abuse.,Do not consume alcohol or other sedatives while under the effects of alfentanil.
Take with or without food consistently at the same times each day.,Do not consume grapefruit or grapefruit juice while on this medication.,Report signs of infection, tremors, or changes in urine output immediately.,Avoid live vaccinations and limit sun exposure due to increased skin cancer risk.,Do not stop or change dose without consulting your doctor.
"Propantheline, an anticholinergic agent, can competitively antagonize muscarinic acetylcholine receptors, potentially reducing gastrointestinal motility and secretion. Alfentanil, a mu-opioid receptor agonist, also decreases gastrointestinal motility through central and peripheral opioid receptors. Concomitant use may synergistically inhibit peristalsis, leading to severe constipation, paralytic ileus, or delayed gastric emptying, which can increase the risk of aspiration and complicate anesthesia recovery."
"Alfentanil, a potent opioid analgesic, can cause significant hypotension and respiratory depression. When combined with furosemide, a loop diuretic that reduces blood volume and vascular resistance, there is a synergistic decrease in blood pressure, which may precipitate cardiovascular collapse, especially in patients with compromised circulatory reserves. Additionally, furosemide may enhance the sedative and respiratory depressant effects of alfentanil, leading to increased risk of respiratory acidosis and altered mental status."
"Alfentanil, a potent mu-opioid receptor agonist, can enhance the bradycardic effects of nebivolol, a beta-1 selective blocker with additional nitric oxide-mediated vasodilation. The combination may lead to excessive slowing of heart rate, reduced cardiac output, and potential hemodynamic instability, particularly in patients with underlying cardiac conduction abnormalities or hypovolemia."
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about ALFENTANIL vs GENGRAF, answered by our medical review team.
ALFENTANIL is a Opioid Analgesic that works by Alfentanil is a potent, short-acting synthetic opioid analgesic that primarily acts as a mu-opioid receptor agonist. It binds to mu-opioid receptors in the central nervous system, leading to G-protein coupled activation of inwardly rectifying potassium channels and inhibition of voltage-gated calcium channels, resulting in hyperpolarization and reduced neurotransmitter release. This produces analgesia, sedation, and respiratory depression.. GENGRAF is a Calcineurin Inhibitor Immunosuppressant that works by Calcineurin inhibitor; binds to cyclophilin, inhibits calcineurin-dependent T-cell activation, preventing nuclear factor of activated T-cells (NF-AT) dephosphorylation and translocation, thereby reducing IL-2 and other cytokine gene transcription.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between ALFENTANIL and GENGRAF depend on the specific clinical indication. These are agents from distinct pharmacological classes and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of ALFENTANIL is: Initial IV bolus of 5-20 mcg/kg; maintenance infusion of 0.5-1.5 mcg/kg/min; incremental boluses of 5-10 mcg/kg as needed. Induction of anesthesia: 50-100 mcg/kg IV.. The standard adult dose of GENGRAF is: 5-15 mg/kg/day orally in divided doses every 12 hours.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between ALFENTANIL and GENGRAF in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. ALFENTANIL is classified as Category C. Alfentanil is an opioid analgesic; limited human data. No clear evidence of major malformations, but third trimester use may cause neonatal opioid withdrawal syndrome (NOWS). Avoid. GENGRAF is classified as Category C. First trimester: Cyclosporine crosses the placenta. Limited human data, but no major malformations attributed. Second and third trimesters: Risk of intrauterine growth restriction,. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.