Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ASTRAMORPH PF vs ALFENTANIL
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Mu-opioid receptor agonist; produces analgesia, sedation, and euphoria by mimicking endogenous endorphins.
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.
Moderate to severe acute pain,Moderate to severe chronic pain,Preoperative sedation,Anesthesia adjunct
Analgesic adjunct during general anesthesia,Induction of anesthesia,Maintenance of anesthesia for short surgical procedures,Off-label: Procedural sedation in monitored settings
Intravenous: 8-10 mg over 2-5 minutes; may be repeated every 8-12 hours as needed. Oral (immediate release): 10-20 mg every 4-6 hours as needed. Oral (extended release): 10-40 mg every 12 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.
Terminal elimination half-life: 2-4 hours; prolonged in renal impairment (up to 12 hours in anuria) and elderly
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 (UGT2B7 and UGT1A3) and minor CYP3A4-mediated N-demethylation to normorphine.
Alfentanil is primarily metabolized by hepatic cytochrome P450 enzymes, mainly CYP3A4, through oxidative N-dealkylation and O-demethylation to inactive metabolites.
Renal: 70-80% unchanged; Biliary/Fecal: 10-20% as metabolites
Primarily hepatic metabolism via CYP3A4; <1% excreted unchanged in urine; metabolites (mainly noralfentanil) excreted renally. Biliary/fecal excretion of metabolites accounts for ~30%.
35% bound; primarily to albumin
~92% bound primarily to alpha-1-acid glycoprotein (AAG) and albumin.
3-5 L/kg; indicates 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: 50-60% (first-pass metabolism); Intramuscular: 80-90%
IV: 100%. IM: ~90%. Epidural: ~30–50% due to local uptake and redistribution. No significant oral bioavailability.
For e GFR 30-50 m L/min: Reduce dose by 25-50% and extend dosing interval to every 12 hours. For e GFR <30 m L/min: Avoid use or reduce dose by 75% and extend interval to every 12-24 hours; monitor for neuroexcitation.
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 A: No adjustment. Child-Pugh B: Reduce dose by 50% every 8-12 hours. Child-Pugh C: Avoid use.
Child-Pugh class A: no adjustment needed; Child-Pugh class B: reduce dose by 50%; Child-Pugh class C: reduce dose by 75%.
Intravenous: 0.1-0.15 mg/kg/dose (max 10 mg) over 2-5 minutes every 8-12 hours as needed. Oral: 0.15-0.3 mg/kg/dose (max 15 mg) every 6-8 hours as needed.
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.
Initial dose should be reduced to 50% of adult dose (oral: 5-10 mg every 6-8 hours; IV: 4-5 mg over 2-5 minutes). Titrate slowly; maximum daily dose 60 mg. Avoid extended-release formulations.
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 exposure; 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, hypotension, seizures, serotonin syndrome, adrenal insufficiency, severe hypotension, biliary tract spasm, and risks in elderly, cachectic, or debilitated patients.
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.
Hypersensitivity to morphine or any component, significant respiratory depression, acute or severe bronchial asthma, GI obstruction, known or suspected paralytic ileus.
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)
No known food interactions. However, alcohol and grapefruit juice may potentiate central nervous system depression and should be avoided.
No significant food interactions known. Avoid grapefruit and grapefruit juice as they may inhibit CYP3A4 metabolism, potentially prolonging effects.
ASTRAMORPH PF (morphine sulfate) is Pregnancy Category C. First trimester: No well-controlled studies; potential for neural tube defects if used with other agents. Second/third trimesters: Chronic use may cause fetal opioid dependence and neonatal abstinence syndrome (NAS). Avoid during labor due to risk of neonatal respiratory depression.
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.
Morphine is excreted into breast milk. M/P ratio is approximately 1:1 to 2:1. Limited data suggest low risk at maternal doses ≤30 mg/day; monitor infant for sedation and respiratory depression. Avoid in mothers with high-dose or prolonged use.
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.
No specific dose adjustment recommended; however, increased clearance in pregnancy may require higher doses for pain control. Use lowest effective dose for shortest duration. Avoid in third trimester near term due to NAS 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.
Astramorph PF (preservative-free morphine sulfate) is indicated for epidural or intrathecal administration. Monitor for delayed respiratory depression, particularly with intrathecal use, as it can occur up to 24 hours post-administration. Use with caution in patients with impaired pulmonary function, head injury, or increased intracranial pressure. Naloxone should be immediately available for reversal. Epidural doses typically range from 2-10 mg; intrathecal doses are 0.1-0.5 mg. Do not use if solution is discolored or contains particulate matter.
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.
Report any difficulty breathing, excessive drowsiness, or nausea immediately.,Avoid driving or operating heavy machinery until you know how this medication affects you.,Do not consume alcohol or other central nervous system depressants while using this medication.,This medication is given directly into the spinal fluid or epidural space; do not attempt to adjust the infusion pump yourself.,If you experience itching, rash, or swelling, contact your healthcare provider.
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.
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 ASTRAMORPH PF vs ALFENTANIL, answered by our medical review team.
ASTRAMORPH PF is a Opioid Analgesic that works by Mu-opioid receptor agonist; produces analgesia, sedation, and euphoria by mimicking endogenous endorphins.. 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 ASTRAMORPH PF 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 ASTRAMORPH PF is: Intravenous: 8-10 mg over 2-5 minutes; may be repeated every 8-12 hours as needed. Oral (immediate release): 10-20 mg every 4-6 hours as needed. Oral (extended release): 10-40 mg every 12 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.
No direct drug-drug interaction has been formally documented between ASTRAMORPH PF and ALFENTANIL 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. ASTRAMORPH PF is classified as Category C. ASTRAMORPH PF (morphine sulfate) is Pregnancy Category C. First trimester: No well-controlled studies; potential for neural tube defects if used with other agents. Second/third tri. 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.