Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
NUMORPHAN vs ALFENTA
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Opioid agonist; binds to mu-opioid receptors in the CNS, inhibiting ascending pain pathways and altering pain perception.
μ-opioid receptor agonist that activates G-protein coupled receptors to inhibit adenylate cyclase, decreasing c AMP production, leading to reduced neuronal excitability and pain transmission.
Moderate to severe pain where an opioid analgesic is appropriate,Anesthesia adjunct (off-label)
Induction and maintenance of anesthesia,Analgesic supplement during surgical procedures,Intravenous use for monitored anesthesia care (MAC)
Intravenous or subcutaneous: 0.5-2 mg (0.1-0.2 mg/kg for severe pain) every 2-3 hours as needed; not to exceed 20 mg/day.
Intravenous: Initial dose 8-20 mcg/kg (0.5-1 min) then 0.5-3 mcg/kg/min or 3-5 mcg/kg q5-20min. For short procedures: 8-20 mcg/kg. For longer procedures: 50-75 mcg/kg followed by 0.5-3 mcg/kg/min.
Terminal elimination half-life is 2–3 hours in adults; prolonged to 3–4 hours in elderly and up to 15 hours in patients with severe hepatic impairment.
Terminal elimination half-life: 90–111 minutes (1.5–1.85 hours); prolonged in hepatic impairment.
Primarily hepatic via glucuronidation; involves UGT2B7; active metabolite (hydromorphone-3-glucuronide) may accumulate in renal impairment.
Hepatic via CYP3A4 to inactive metabolites; major metabolite is desmethylalfentanil (inactive).
Primarily renal (approximately 70% as unchanged drug, <5% as noroxymorphone and other conjugates); biliary/fecal excretion accounts for ~20%.
Primarily renal (urinary) elimination as metabolites; approximately 80% recovered in urine, 20% in feces.
Approximately 10–20% bound to plasma proteins (primarily albumin).
Approximately 92% bound, primarily to alpha-1 acid glycoprotein and albumin.
2.5–3.5 L/kg; indicates extensive tissue distribution, with high affinity for brain and other tissues.
0.5–1.0 L/kg; reflects moderate tissue distribution; higher Vd in neonates and elderly.
Intravenous: 100%; Intramuscular: approximately 85–95%; Subcutaneous: approximately 75–85%; Oral: approximately 10–20% due to extensive first-pass metabolism.
Intravenous: 100%; intramuscular: approximately 90%; intrathecal: approximately 10% (due to systemic absorption following spinal administration).
Cr Cl 10-50 m L/min: administer 75% of dose; Cr Cl <10 m L/min: administer 50% of dose, use with caution, consider extended dosing intervals.
No specific dose adjustment is recommended for renal impairment; however, alfentanil is primarily metabolized in the liver and its pharmacokinetics are not significantly altered in renal failure.
Child-Pugh Class B: reduce dose by 50%; Child-Pugh Class C: reduce dose by 75% or avoid use; start at lowest dose and titrate carefully.
In hepatic impairment (Child-Pugh class A, B, C): Reduce dose by 50% and titrate carefully due to prolonged elimination half-life. Consider lower initial doses and extended dosing intervals.
Children >2 years: 0.1-0.2 mg/kg intravenously, subcutaneously, or intramuscularly every 2-4 hours as needed; not to exceed 15 mg/day.
Children (1-12 years): Induction of anesthesia: 10-20 mcg/kg IV; maintenance: 5-10 mcg/kg IV or infusion 0.5-1 mcg/kg/min. For neonates and infants: Dose individualization required; titrate to effect.
Start at low end of dosing range (0.5 mg), extend dosing interval to 3-4 hours, monitor for respiratory depression and constipation, use non-opioid alternatives when possible.
Elderly patients (>65 years): Reduce initial dose by 30-50% and administer slowly. Due to decreased clearance and increased sensitivity, lower infusion rates (e.g., 0.3-0.5 mcg/kg/min) may be needed.
Risk of respiratory depression, especially in elderly, cachectic, or debilitated patients; concomitant use with benzodiazepines or CNS depressants may cause profound sedation, respiratory depression, coma, and death; abuse potential leading to addiction; neonatal opioid withdrawal syndrome with prolonged use during pregnancy.
Risk of respiratory depression, particularly in elderly or debilitated patients. Concomitant use with benzodiazepines or other CNS depressants may cause profound sedation, respiratory depression, coma, and death.
Respiratory depression; CNS depression; serotonin syndrome (with serotonergic drugs); adrenal insufficiency; hypotension; seizures; opioid-induced hyperalgesia; impaired ability to drive/operate machinery; risk of overdose with alcohol or other CNS depressants.
Respiratory depression; abuse potential; hypotension; bradycardia; muscle rigidity; serotonin syndrome with concurrent serotonergic drugs; adrenal insufficiency; risk of withdrawal with prolonged use.
Hypersensitivity to hydromorphone or any component; significant respiratory depression; acute or severe bronchial asthma; known or suspected paralytic ileus; concurrent use of MAOIs (or within 14 days).
Hypersensitivity to alfentanil or any component; significant respiratory insufficiency; severe asthma; paralytic ileus; concurrent use of MAOIs (or within 14 days); acute or postoperative pain management in children (except for procedural sedation).
Avoid alcohol and grapefruit juice. Grapefruit juice may inhibit CYP3A4 metabolism of oxymorphone, leading to increased plasma concentrations and risk of toxicity. High-fat meals may delay absorption but not significantly alter overall exposure. Maintain adequate hydration to prevent constipation.
No known interactions with food. However, grapefruit juice may increase alfentanil serum concentrations due to CYP3A4 inhibition; avoid concurrent consumption.
First trimester: Limited data, but opioid use is associated with neural tube defects and congenital heart defects in some studies. Second and third trimesters: Chronic use may lead to fetal opioid dependence and neonatal withdrawal syndrome. No specific malformation pattern attributed to Numorphan. Avoid prolonged use, especially in first trimester.
Alfentanil, a short-acting opioid analgesic, is classified as FDA Pregnancy Category C. No well-controlled studies in pregnant women exist. In animal studies, no teratogenic effects were observed at clinically relevant doses; however, high doses caused embryotoxicity and increased fetal mortality. Trimester-specific risks: First trimester - potential for minor malformations based on limited human data; second trimester - possible risk if used chronically; third trimester - prolonged use may lead to neonatal respiratory depression, withdrawal syndrome, or opioid dependence. Use only if benefits outweigh risks.
Numorphan (oxymorphone) is excreted into breast milk. The M/P ratio is unknown. Limited data suggest low concentrations, but caution is advised. Monitor infant for drowsiness, respiratory depression, and withdrawal if maternal use is prolonged. American Academy of Pediatrics considers it compatible with breastfeeding with cautious use, but consider risk-benefit.
Alfentanil is excreted into human breast milk in low concentrations. The milk-to-plasma (M/P) ratio is approximately 0.3. Estimated infant dose is <1% of maternal weight-adjusted dose, which is considered clinically insignificant. However, due to potential for neonatal opioid effects, caution is advised; monitor infant for drowsiness, respiratory depression, and feeding difficulties. Consider alternative analgesics with established safety profiles, such as acetaminophen or ibuprofen, for lactation.
Pregnancy increases renal blood flow and hepatic metabolism; clearance of oxymorphone may be increased. No formal studies available. Consider dose adjustments based on clinical response and tolerability. Avoid in first trimester if possible; if necessary, use lowest effective dose for shortest duration. In third trimester, anticipate potential neonatal withdrawal and plan for taper postpartum.
Pregnancy can alter pharmacokinetics of alfentanil. Increased plasma volume and distribution may require higher doses to achieve same effect, while decreased plasma protein binding may increase free fraction, potentiating effects. Alpha-1-acid glycoprotein levels change in pregnancy, affecting binding. In third trimester, clearance may be increased by up to 50% due to enhanced hepatic metabolism. Therefore, dose adjustments may be needed: consider starting at low dose and titrating to effect, with close monitoring. For intravenous administration, typical adult doses (5-20 μg/kg) may need adjustments; no standard pregnancy-specific dosing exists. Use the lowest effective dose for the shortest duration. In labor, avoid high doses prior to delivery due to risk of neonatal respiratory depression.
Numorphan (oxymorphone) is a potent semisynthetic opioid agonist approximately 10 times more potent than morphine. Avoid in patients with severe respiratory depression, paralytic ileus, or acute asthma. Caution in elderly, cachectic, or debilitated patients due to increased risk of respiratory depression. Monitor for hypotension and bradycardia. Use with extreme caution in patients with head injury or increased intracranial pressure. Abrupt discontinuation may precipitate withdrawal; taper gradually.
Alfentanil is a potent, rapid-onset, short-acting opioid analgesic used primarily for induction and maintenance of anesthesia. Due to its high protein binding (90%) and rapid redistribution, it has a shorter duration of action than fentanyl, making it suitable for brief, painful procedures. It undergoes hepatic metabolism via CYP3A4, so concomitant use with CYP3A4 inhibitors like ketoconazole or erythromycin can prolong its effects. Use caution in elderly or hypovolemic patients due to increased risk of hypotension. Naloxone reverses respiratory depression. Alfentanil is 5-10 times less potent than fentanyl.
Take exactly as prescribed; do not increase dose or frequency without consulting your doctor.,Numorphan may cause dizziness, drowsiness, or blurred vision; avoid driving or operating heavy machinery until you know how the drug affects you.,Avoid alcohol and other central nervous system depressants (e.g., sedatives, tranquilizers) as they may increase the risk of serious side effects like respiratory depression.,If you miss a dose, skip it and take the next dose at the scheduled time; do not double up.,Do not suddenly stop taking this medication; a gradual reduction under medical supervision is needed to prevent withdrawal symptoms.,Store securely away from children and pets; dispose of unused medication via a drug take-back program.
This medication is given only by a healthcare professional in a hospital or surgical setting.,You may feel drowsy, dizzy, or nauseated after receiving this drug.,Report any difficulty breathing or slow heart rate to your healthcare provider immediately.,Avoid alcohol and sedatives for 24 hours after administration, as they can increase side effects.,Do not drive or operate machinery until the effects have fully worn off.
No interactions on record
"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 NUMORPHAN vs ALFENTA, answered by our medical review team.
NUMORPHAN is a Opioid Analgesic that works by Opioid agonist; binds to mu-opioid receptors in the CNS, inhibiting ascending pain pathways and altering pain perception.. ALFENTA is a Opioid Analgesic that works by μ-opioid receptor agonist that activates G-protein coupled receptors to inhibit adenylate cyclase, decreasing c AMP production, leading to reduced neuronal excitability and pain transmission.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between NUMORPHAN and ALFENTA 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 NUMORPHAN is: Intravenous or subcutaneous: 0.5-2 mg (0.1-0.2 mg/kg for severe pain) every 2-3 hours as needed; not to exceed 20 mg/day.. The standard adult dose of ALFENTA is: Intravenous: Initial dose 8-20 mcg/kg (0.5-1 min) then 0.5-3 mcg/kg/min or 3-5 mcg/kg q5-20min. For short procedures: 8-20 mcg/kg. For longer procedures: 50-75 mcg/kg followed by 0.5-3 mcg/kg/min.. 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 NUMORPHAN and ALFENTA 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. NUMORPHAN is classified as Category C. First trimester: Limited data, but opioid use is associated with neural tube defects and congenital heart defects in some studies. Second and third trimesters: Chronic use may lead. ALFENTA is classified as Category C. Alfentanil, a short-acting opioid analgesic, is classified as FDA Pregnancy Category C. No well-controlled studies in pregnant women exist. In animal studies, no teratogenic effect. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.