Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ALFENTA vs EVZIO
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
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.
Naloxone is an opioid antagonist that competitively binds to mu-opioid receptors, reversing opioid-induced respiratory depression and analgesia.
Induction and maintenance of anesthesia,Analgesic supplement during surgical procedures,Intravenous use for monitored anesthesia care (MAC)
Emergency treatment of known or suspected opioid overdose, as manifested by respiratory and/or central nervous system depression.
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.
2 mg intramuscular (IM) or subcutaneous (SC) autoinjector into anterolateral thigh; repeat every 2-3 minutes as needed for opioid overdose.
Terminal elimination half-life: 90–111 minutes (1.5–1.85 hours); prolonged in hepatic impairment.
The terminal elimination half-life of naloxone in adults is approximately 1-2 hours. In neonates, half-life may be prolonged to 3-4 hours. Clinical context: Short half-life necessitates repeated dosing or continuous infusion for sustained opioid reversal, especially with long-acting opioids.
Hepatic via CYP3A4 to inactive metabolites; major metabolite is desmethylalfentanil (inactive).
Primarily hepatic glucuronidation, with N-allylnoroxymorphone as the major metabolite; CYP450 system not significantly involved.
Primarily renal (urinary) elimination as metabolites; approximately 80% recovered in urine, 20% in feces.
Naloxone undergoes extensive hepatic metabolism primarily via glucuronidation, with approximately 70% excreted in urine as naloxone-3-glucuronide. About 25% is excreted in feces via biliary elimination. Less than 1% is excreted unchanged in urine.
Approximately 92% bound, primarily to alpha-1 acid glycoprotein and albumin.
Approximately 30-40% bound to plasma proteins, mainly albumin.
0.5–1.0 L/kg; reflects moderate tissue distribution; higher Vd in neonates and elderly.
Volume of distribution is approximately 2-3 L/kg, indicating extensive distribution into tissues beyond plasma volume. Clinical meaning: High Vd suggests rapid distribution and short half-life.
Intravenous: 100%; intramuscular: approximately 90%; intrathecal: approximately 10% (due to systemic absorption following spinal administration).
Intramuscular bioavailability is approximately 100% (assumed complete absorption). Oral bioavailability is <2% due to extensive first-pass metabolism; therefore, not used orally.
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.
No dose adjustment required for renal impairment.
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.
No dose adjustment required for hepatic impairment.
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.
Weight-based: <20 kg: 0.1 mg/kg IM/SC; ≥20 kg: 2 mg IM/SC; repeat every 2-3 minutes if needed.
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.
No specific dose adjustment; use standard adult dosing with monitoring for adverse effects due to potential comorbidities.
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.
Risk of recurrent respiratory depression: The duration of action of naloxone is shorter than that of most opioids, so repeat doses may be necessary. Patients should be monitored until respiratory function is fully recovered.
Respiratory depression; abuse potential; hypotension; bradycardia; muscle rigidity; serotonin syndrome with concurrent serotonergic drugs; adrenal insufficiency; risk of withdrawal with prolonged use.
May precipitate acute opioid withdrawal in opioid-dependent patients; risk of incomplete response or need for repeat doses due to short half-life; not effective for non-opioid overdoses; avoid in known hypersensitivity; use caution in patients with cardiovascular disease or those taking cardiotoxic drugs.
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).
Hypersensitivity to naloxone or any component of the formulation.
No known interactions with food. However, grapefruit juice may increase alfentanil serum concentrations due to CYP3A4 inhibition; avoid concurrent consumption.
None known; naloxone is not absorbed orally due to first-pass metabolism. No dietary restrictions.
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.
EVZIO (naloxone) is not associated with major congenital malformations; limited data in pregnancy. Immediate reversal of opioid effects may precipitate withdrawal in the fetus, potentially causing adverse outcomes such as preterm labor or fetal distress. Third trimester use may cause neonatal opioid withdrawal syndrome (NOWS) in opioid-dependent mothers if naloxone is administered.
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.
Naloxone is unlikely to be excreted in breast milk in significant amounts due to low bioavailability. M/P ratio not established. Preterm infusion studies show minimal transfer. Consider benefits of breastfeeding against risk of maternal opioid overdose reversal.
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.
No pharmacokinetic studies in pregnancy demonstrate need for dose adjustment. Standard dosing (0.4 mg or 2 mg intranasal/IM) is used. Pregnant patients may require higher doses due to increased volume of distribution and metabolic changes, but evidence insufficient to recommend routine dose adjustment.
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.
EVZIO is a naloxone auto-injector for emergency treatment of opioid overdose. Administer intramuscularly or subcutaneously into outer thigh; can be given through clothing. Repeat every 2-3 minutes if no response. Onset of action within 2-5 minutes. Duration shorter than most opioids; monitor for recurrence of respiratory depression. Not for non-opioid overdoses.
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.
Always call 911 immediately after giving EVZIO.,Place the device against the outer thigh and press firmly; it will automatically inject.,A short, clicking sound indicates the injection has started.,Stay with the person after injection; they may become agitated due to opioid withdrawal.,Store at room temperature; check expiration date regularly.,Tell family and friends where you keep EVZIO.
"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 ALFENTA vs EVZIO, answered by our medical review team.
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.. EVZIO is a Opioid Antagonist that works by Naloxone is an opioid antagonist that competitively binds to mu-opioid receptors, reversing opioid-induced respiratory depression and analgesia.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between ALFENTA and EVZIO 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 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.. The standard adult dose of EVZIO is: 2 mg intramuscular (IM) or subcutaneous (SC) autoinjector into anterolateral thigh; repeat every 2-3 minutes as needed for opioid overdose.. 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 ALFENTA and EVZIO 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. 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. EVZIO is classified as Category C. EVZIO (naloxone) is not associated with major congenital malformations; limited data in pregnancy. Immediate reversal of opioid effects may precipitate withdrawal in the fetus, pot. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.