Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
DARVON-N vs ALFENTA
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Propoxyphene is a weak mu-opioid receptor agonist that produces analgesia by binding to opioid receptors in the central nervous system, altering the perception of and response to pain. Its metabolite norpropoxyphene has local anesthetic and sodium channel blocking effects, which may contribute to cardiac toxicity.
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.
Mild to moderate pain,Off-label: None established
Induction and maintenance of anesthesia,Analgesic supplement during surgical procedures,Intravenous use for monitored anesthesia care (MAC)
100 mg orally every 4 hours as needed for pain; maximum 600 mg per 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.
Propoxyphene: 6-12 hours; norpropoxyphene: 30-36 hours. Accumulation of norpropoxyphene on repeated dosing increases risk of toxicity.
Terminal elimination half-life: 90–111 minutes (1.5–1.85 hours); prolonged in hepatic impairment.
Primarily hepatic via CYP3A4 and CYP2D6 to norpropoxyphene (active metabolite). Propoxyphene and norpropoxyphene undergo further metabolism and conjugation.
Hepatic via CYP3A4 to inactive metabolites; major metabolite is desmethylalfentanil (inactive).
Primarily renal (approximately 70% as unchanged drug and glucuronide conjugates); minor biliary/fecal elimination (25-30%).
Primarily renal (urinary) elimination as metabolites; approximately 80% recovered in urine, 20% in feces.
Propoxyphene: 70-80%; norpropoxyphene: 75-85%. Primarily bound to albumin.
Approximately 92% bound, primarily to alpha-1 acid glycoprotein and albumin.
Propoxyphene: 12-26 L/kg; widely distributed into tissues, including CNS.
0.5–1.0 L/kg; reflects moderate tissue distribution; higher Vd in neonates and elderly.
Oral: approximately 30-70% due to extensive first-pass metabolism; interindividual variability.
Intravenous: 100%; intramuscular: approximately 90%; intrathecal: approximately 10% (due to systemic absorption following spinal administration).
GFR 30-89 m L/min: no adjustment; GFR <30 m L/min: reduce dose by 50% or extend interval to every 8-12 hours; not recommended for 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: no adjustment; Child-Pugh Class B: reduce dose by 50%; Child-Pugh 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 for children under 12 years; for adolescents 12-17 years: 100 mg every 4 hours as needed, maximum 400 mg per 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.
Initiate at 50 mg every 4 hours as needed; maximum 400 mg per day; monitor for CNS depression and constipation.
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.
DARVON-N (propoxyphene) is contraindicated in patients with a history of drug abuse, and its use should be monitored for signs of abuse, addiction, or misuse. It should not be used in patients with severe respiratory depression, acute or severe bronchial asthma, or known hypersensitivity to propoxyphene. Additionally, because of the risk of QT prolongation and cardiac arrhythmias, propoxyphene-containing products were withdrawn from the US market in 2010.
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.
Addiction, abuse, and misuse,Respiratory depression,Accidental ingestion (especially in children) can be fatal,Neonatal opioid withdrawal syndrome,Interactions with CNS depressants (e.g., alcohol, benzodiazepines),Elderly or debilitated patients: increased risk of respiratory depression,Hepatic or renal impairment,QT prolongation and risk of torsade de pointes
Respiratory depression; abuse potential; hypotension; bradycardia; muscle rigidity; serotonin syndrome with concurrent serotonergic drugs; adrenal insufficiency; risk of withdrawal with prolonged use.
Hypersensitivity to propoxyphene or any component,Significant respiratory depression,Acute or severe bronchial asthma in an unmonitored setting,Known or suspected gastrointestinal obstruction (e.g., paralytic ileus),Concurrent use of alcohol, sedatives, or other CNS depressants,History of substance abuse,Concurrent 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; may enhance CNS depression. No specific food interactions known, but high-fat meals may delay absorption.
No known interactions with food. However, grapefruit juice may increase alfentanil serum concentrations due to CYP3A4 inhibition; avoid concurrent consumption.
First trimester: Limited data; potential for neural tube defects with first-trimester exposure. Second and third trimesters: Risk of premature closure of ductus arteriosus, oligohydramnios, and neonatal withdrawal syndrome. Use only if clearly needed.
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.
Propoxyphene is excreted into breast milk with a milk-to-plasma ratio of approximately 1.0. Theoretical risk of neonatal respiratory depression and withdrawal. Not recommended; consider alternative analgesics.
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 in pregnancy may necessitate higher doses; however, due to risks, avoid use or limit to lowest effective dose for shortest duration. No established dose adjustment guidelines.
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.
Darvon-N (propoxyphene napsylate) is a weak opioid analgesic with efficacy similar to codeine; its use is limited by narrow therapeutic index and risk of QT prolongation. It is metabolized by CYP2D6 to norpropoxyphene, which has a long half-life and can accumulate, causing CNS toxicity. Due to safety concerns, it has been withdrawn from many markets; avoid in patients with substance use disorder, renal impairment, or those taking CNS depressants. Monitor for QTc prolongation if used with other QT-prolonging agents.
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 due to risk of serious side effects including seizures and cardiac arrhythmias.,Avoid alcohol and other CNS depressants (e.g., benzodiazepines, sedatives) as they increase risk of respiratory depression and sedation.,Do not stop abruptly after prolonged use; withdrawal symptoms may occur.,Store securely out of reach of children; dispose of unused medication properly.,Use caution when driving or operating machinery; may cause dizziness or drowsiness.,Report new or worsening shortness of breath, irregular heartbeat, or fainting to your healthcare provider.
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 DARVON-N vs ALFENTA, answered by our medical review team.
DARVON-N is a Opioid Analgesic that works by Propoxyphene is a weak mu-opioid receptor agonist that produces analgesia by binding to opioid receptors in the central nervous system, altering the perception of and response to pain. Its metabolite norpropoxyphene has local anesthetic and sodium channel blocking effects, which may contribute to cardiac toxicity.. 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 DARVON-N 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 DARVON-N is: 100 mg orally every 4 hours as needed for pain; maximum 600 mg per 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 DARVON-N 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. DARVON-N is classified as Category C. First trimester: Limited data; potential for neural tube defects with first-trimester exposure. Second and third trimesters: Risk of premature closure of ductus arteriosus, oligohy. 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.