Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
AVINZA vs ALFENTA
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
AVINZA (morphine sulfate) is a full opioid agonist that binds to mu-opioid receptors in the CNS, producing analgesia by altering pain perception and emotional response to pain.
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.
Management of opioid-experienced patients with moderate to severe chronic pain requiring daily, around-the-clock opioid therapy for an extended period of time
Induction and maintenance of anesthesia,Analgesic supplement during surgical procedures,Intravenous use for monitored anesthesia care (MAC)
Oral, 30 mg once daily (q24h) for opioid-naïve patients; titrate based on response. Maximum daily dose 160 mg. Administer with food to minimize peak effects.
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 of morphine is approximately 1.5-2 hours; however, due to the extended-release formulation, the effective half-life is prolonged to about 9-11 hours, allowing once-daily dosing.
Terminal elimination half-life: 90–111 minutes (1.5–1.85 hours); prolonged in hepatic impairment.
Primarily hepatic via glucuronidation by UGT2B7 to morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G); minor CYP2C9 involvement.
Hepatic via CYP3A4 to inactive metabolites; major metabolite is desmethylalfentanil (inactive).
Primarily renal (approximately 90% as morphine metabolites, mainly morphine-3-glucuronide and morphine-6-glucuronide); biliary/fecal excretion accounts for less than 10%.
Primarily renal (urinary) elimination as metabolites; approximately 80% recovered in urine, 20% in feces.
Approximately 30-40% bound to plasma proteins, primarily albumin.
Approximately 92% bound, primarily to alpha-1 acid glycoprotein and albumin.
Approximately 3-4 L/kg, indicating extensive tissue distribution.
0.5–1.0 L/kg; reflects moderate tissue distribution; higher Vd in neonates and elderly.
Oral bioavailability of morphine is variable (approximately 20-40%) due to extensive first-pass metabolism; the extended-release formulation provides consistent absorption over 24 hours.
Intravenous: 100%; intramuscular: approximately 90%; intrathecal: approximately 10% (due to systemic absorption following spinal administration).
For GFR 30-59 m L/min: initiate at 50% of usual dose and titrate carefully; GFR <30 m L/min: initiate at 25% of usual dose; avoid in severe renal impairment (GFR <15 m L/min).
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 A: initiate at 50% of usual dose; Class B: initiate at 25% of usual dose; Class C: avoid use.
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.
Not recommended in pediatric patients <18 years; safety and efficacy not established. For adolescent patients (≥18 kg), off-label use: 0.1-0.2 mg/kg/dose q4-6h PRN; extended-release formulations not intended for children.
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.
For patients ≥65 years: initiate at 50% of adult dose (15 mg once daily) and titrate cautiously due to increased sensitivity, reduced renal/hepatic function, and higher risk of respiratory depression. Consider lower starting doses and extended intervals.
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.
WARNING: ADDICTION, ABUSE, AND MISUSE; LIFE-THREATENING RESPIRATORY DEPRESSION; ACCIDENTAL INGESTION; NEONATAL OPIOID WITHDRAWAL SYNDROME; AND RISKS FROM CONCOMITANT USE WITH BENZODIAZEPINES OR OTHER CNS DEPRESSANTS.
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 life-threatening respiratory depression; addiction, abuse, and misuse; neonatal opioid withdrawal syndrome; interactions with CNS depressants; severe hypotension; gastrointestinal obstruction; seizure risk; impaired mental or physical abilities.
Respiratory depression; abuse potential; hypotension; bradycardia; muscle rigidity; serotonin syndrome with concurrent serotonergic drugs; adrenal insufficiency; risk of withdrawal with prolonged use.
Significant respiratory depression; acute or severe bronchial asthma in an unmonitored setting or without resuscitative equipment; known or suspected gastrointestinal obstruction; paralytic ileus; hypersensitivity to morphine sulfate.
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 alcohol-containing products (e.g., some mouthwashes, extracts) due to risk of dose dumping. Grapefruit juice may increase morphine bioavailability; limit intake. High-fat meals may delay absorption but not significantly alter overall exposure.
No known interactions with food. However, grapefruit juice may increase alfentanil serum concentrations due to CYP3A4 inhibition; avoid concurrent consumption.
First trimester: Limited human data; animal studies show no evidence of teratogenicity at clinically relevant doses. Second and third trimesters: Prolonged use may cause neonatal opioid withdrawal syndrome (NOWS) and respiratory depression at birth. Avoid chronic use near term.
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.
Morphine is excreted into breast milk; M/P ratio approximately 1:1. Infant exposure is dose-dependent; monitor for sedation, respiratory depression, and withdrawal. Use with caution; avoid in breastfeeding women with known infant risk factors.
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.
Increased clearance and volume of distribution during late pregnancy may require dose adjustments. Use lowest effective dose for shortest duration. Avoid extended-release formulations near term; consider immediate-release morphine for acute pain management.
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.
AVINZA is an extended-release morphine formulation using the SODAS (Spheroidal Oral Drug Absorption System) technology, consisting of immediate-release and sustained-release beads. It must be taken whole; crushing or chewing can lead to rapid release and fatal overdose. Do not use in opioid-naïve patients; initiate with lower strengths if converting from other opioids. Monitor for signs of serotonin syndrome when co-administered with serotonergic drugs. Avoid alcohol consumption; ethanol can cause dose dumping.
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 this medication exactly as prescribed; do not crush, chew, or break the capsules.,Swallow the capsules whole; if you have trouble swallowing, you may open the capsules and sprinkle the beads onto a small amount of soft food (e.g., applesauce) and swallow immediately without chewing.,Do not consume alcohol or any products containing alcohol while taking AVINZA, as it can lead to a dangerous increase in morphine levels.,This medication has a high risk of addiction, abuse, and misuse; store it safely and dispose of unused tablets properly.,Common side effects include constipation, nausea, drowsiness, and dizziness; report severe or persistent symptoms to your doctor.,Do not stop suddenly; withdrawal symptoms may occur; your doctor will guide you on tapering the dose.,Avoid driving or operating heavy machinery until you know how this medication affects you.
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 AVINZA vs ALFENTA, answered by our medical review team.
AVINZA is a Opioid Analgesic that works by AVINZA (morphine sulfate) is a full opioid agonist that binds to mu-opioid receptors in the CNS, producing analgesia by altering pain perception and emotional response to pain.. 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 AVINZA 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 AVINZA is: Oral, 30 mg once daily (q24h) for opioid-naïve patients; titrate based on response. Maximum daily dose 160 mg. Administer with food to minimize peak effects.. 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 AVINZA 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. AVINZA is classified as Category C. First trimester: Limited human data; animal studies show no evidence of teratogenicity at clinically relevant doses. Second and third trimesters: Prolonged use may cause neonatal o. 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.