Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
LEVORPHANOL TARTRATE vs ALFENTANIL
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Levorphanol is a potent opioid analgesic that acts as a mu-opioid receptor agonist. It also has NMDA receptor antagonist activity, inhibits norepinephrine and serotonin reuptake, and acts as a sigma receptor agonist, contributing to its analgesic effects and reduced tolerance development.
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.
Management of moderate to severe pain where opioid treatment is appropriate,Off-label: treatment-refractory neuropathic pain, chronic pain syndromes
Analgesic adjunct during general anesthesia,Induction of anesthesia,Maintenance of anesthesia for short surgical procedures,Off-label: Procedural sedation in monitored settings
2 mg orally every 6-8 hours as needed for pain; for opioid-tolerant patients, doses up to 4 mg orally every 6-8 hours may be used. Parenterally: 1-2 mg subcutaneously or intramuscularly every 6-8 hours; may be given intravenously at 0.5-1 mg every 6-8 hours.
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.
11-16 hours; extended in hepatic impairment (up to 30 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.
Primarily hepatic via glucuronidation and N-demethylation; CYP450 involvement not fully characterized.
Alfentanil is primarily metabolized by hepatic cytochrome P450 enzymes, mainly CYP3A4, through oxidative N-dealkylation and O-demethylation to inactive metabolites.
Renal: approximately 30% as unchanged drug and 50% as glucuronide conjugates; fecal: 20% via biliary excretion.
Primarily hepatic metabolism via CYP3A4; <1% excreted unchanged in urine; metabolites (mainly noralfentanil) excreted renally. Biliary/fecal excretion of metabolites accounts for ~30%.
Approximately 50% bound to albumin.
~92% bound primarily to alpha-1-acid glycoprotein (AAG) and albumin.
10-15 L/kg; extensive tissue distribution.
Vd: 0.4–1.0 L/kg (mean ~0.75 L/kg). Moderate Vd reflecting rapid distribution to tissues, especially brain and muscle.
Oral: 50-70% (first-pass effect); intravenous: 100%.
IV: 100%. IM: ~90%. Epidural: ~30–50% due to local uptake and redistribution. No significant oral bioavailability.
Cr Cl 10-50 m L/min: Administer 75% of usual dose at extended intervals (e.g., every 12 hours). Cr Cl <10 m L/min: Administer 50% of usual dose at extended intervals (e.g., every 12-24 hours). For patients on dialysis, use with caution and reduce dose; not well-studied.
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.
Child-Pugh Class A: No adjustment needed. Child-Pugh Class B: Reduce dose by 50% and administer at extended intervals (e.g., every 12 hours). Child-Pugh Class C: Avoid use; if necessary, reduce dose by 75% and monitor closely.
Child-Pugh class A: no adjustment needed; Child-Pugh class B: reduce dose by 50%; Child-Pugh class C: reduce dose by 75%.
Not recommended for use in pediatric patients due to lack of safety and efficacy data; use in children under 18 years is generally avoided. For palliative care in older children, consult specialist.
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.
Start at 50% of the usual adult dose (e.g., 1 mg orally every 6-8 hours) due to increased sensitivity and reduced clearance; titrate carefully with close monitoring for respiratory depression and constipation.
Reduce initial IV bolus by 30-50% to 3-10 mcg/kg; titrate carefully; monitor for prolonged sedation and respiratory depression.
Risk of addiction, abuse, and misuse; life-threatening respiratory depression; accidental ingestion; neonatal opioid withdrawal syndrome; risks from concomitant use with benzodiazepines or other CNS depressants.
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.
Respiratory depression: potentially fatal, especially at initiation and dose escalation,Adrenal insufficiency,Severe hypotension,Seizures,Serotonin syndrome,Risks from concomitant CNS depressants,Impaired mental or physical abilities
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.
Significant respiratory depression,Acute or severe bronchial asthma,Known or suspected gastrointestinal obstruction,Concurrent use of MAOIs or within 14 days,Hypersensitivity to levorphanol
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)
Avoid grapefruit juice as it may increase levorphenol levels via CYP3A4 inhibition. High-fat meals may delay absorption but not overall extent. Alcohol must be avoided due to additive CNS depression.
No significant food interactions known. Avoid grapefruit and grapefruit juice as they may inhibit CYP3A4 metabolism, potentially prolonging effects.
Levorphanol is an opioid agonist; limited data in pregnancy. First trimester: potential for neural tube defects based on animal studies; human risk unclear. Second/third trimesters: risk of fetal opioid dependence, preterm labor, and intrauterine growth restriction. Use only if benefit outweighs risk.
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.
Unknown if levorphanol is excreted in human milk; other opioids are present in breast milk. Consider benefits of breastfeeding vs. risk of infant opioid exposure (respiratory depression, withdrawal). M/P ratio not established.
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.
Pregnancy may alter opioid pharmacokinetics (increased clearance, volume of distribution). Dose adjustments may be needed to maintain analgesic efficacy; consider lower starting doses and titrate to effect. Avoid use during first and third trimesters; taper to avoid withdrawal if discontinuing. No specific dose adjustment guidelines are established; individualize based on response and risk.
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.
Levorphanol is a potent mu-opioid agonist with a long half-life (12-16 hours) and active metabolites; avoid use in opioid-naive patients due to risk of respiratory depression. It has NMDA antagonist activity, which may provide benefit in neuropathic pain but also contributes to psychotomimetic effects. Equianalgesic dose: 2 mg oral levorphenol ≈ 10 mg morphine. Accumulation occurs with repeated dosing; monitor for sedation and respiratory depression.
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.
Take exactly as prescribed; do not increase dose or frequency without consulting your doctor.,Avoid alcohol and other CNS depressants (e.g., benzodiazepines, sedatives) as they increase risk of severe drowsiness and breathing problems.,Do not drive or operate heavy machinery until you know how levorphenol affects you.,Do not stop abruptly; withdrawal symptoms may occur. Taper under medical supervision.,Constipation is common; increase fluid and fiber intake, and consider stool softeners.,Store securely out of reach of others, as misuse can cause overdose and death.,Report any difficulty breathing, severe drowsiness, or confusion immediately.
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.
"The combination of Biperiden, an anticholinergic agent used for Parkinsonism, and Levorphanol, a potent opioid analgesic, can lead to additive central nervous system depression and increased anticholinergic side effects. Specifically, both drugs can cause sedation, confusion, and respiratory depression, particularly in elderly patients or those with compromised central nervous system function. Additionally, the anticholinergic effects of Biperiden (e.g., dry mouth, urinary retention, constipation) may be exacerbated by Levorphanol, which also has mild anticholinergic properties, leading to enhanced adverse effects."
"The combination of meprobamate, a carbamate anxiolytic with central nervous system (CNS) depressant properties, and levorphanol, a potent opioid analgesic, results in additive or synergistic CNS depression. This leads to increased risks of profound sedation, respiratory depression, coma, and death. Patients experience compounded impairment of cognitive and motor functions, necessitating cautious use or avoidance."
"Levorphanol, a potent mu-opioid receptor agonist, and Bromazepam, a benzodiazepine acting as a positive allosteric modulator of GABA-A receptors, synergistically depress the central nervous system (CNS), particularly affecting respiratory centers in the brainstem. This combination significantly increases the risk of severe respiratory depression, hypotension, profound sedation, coma, and death. Additive CNS depression can also impair cognitive and motor function, increasing fall risk and accidental injury."
"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."
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about LEVORPHANOL TARTRATE vs ALFENTANIL, answered by our medical review team.
LEVORPHANOL TARTRATE is a Opioid Analgesic that works by Levorphanol is a potent opioid analgesic that acts as a mu-opioid receptor agonist. It also has NMDA receptor antagonist activity, inhibits norepinephrine and serotonin reuptake, and acts as a sigma receptor agonist, contributing to its analgesic effects and reduced tolerance development.. 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.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between LEVORPHANOL TARTRATE and ALFENTANIL depend on the specific clinical indication. These are both Opioid Analgesic agents and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of LEVORPHANOL TARTRATE is: 2 mg orally every 6-8 hours as needed for pain; for opioid-tolerant patients, doses up to 4 mg orally every 6-8 hours may be used. Parenterally: 1-2 mg subcutaneously or intramuscularly every 6-8 hours; may be given intravenously at 0.5-1 mg every 6-8 hours.. 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.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
A moderate-severity drug interaction has been identified when combining LEVORPHANOL TARTRATE and ALFENTANIL. The risk or severity of adverse effects can be increased when Alfentanil is combined with Levorphanol. Consult your prescriber before combining these medications.
The maternal-fetal safety profiles differ. LEVORPHANOL TARTRATE is classified as Category C. Levorphanol is an opioid agonist; limited data in pregnancy. First trimester: potential for neural tube defects based on animal studies; human risk unclear. Second/third trimesters. 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. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.