Comparative Pharmacology
Head-to-head clinical analysis: DARVON W ASA versus DARVON N W ASA.
Peer-Reviewed Evidence
Head-to-head clinical analysis: DARVON W ASA versus DARVON N W ASA.
DARVON W/ ASA vs DARVON-N W/ ASA
Head-to-head clinical comparison of therapeutic indices and safety profiles.
Combination analgesic: propoxyphene is a weak opioid agonist binding to mu-opioid receptors, inhibiting ascending pain pathways; aspirin irreversibly inhibits cyclooxygenase-1 and -2, reducing prostaglandin synthesis.
Propoxyphene is a weak opioid agonist that binds to mu-opioid receptors in the CNS, altering pain perception. Aspirin inhibits cyclooxygenase (COX-1 and COX-2), reducing prostaglandin synthesis, which mediates pain, fever, and inflammation.
Mild to moderate painPain accompanied by inflammation or fever
Mild to moderate painPain accompanied by fever (off-label use of aspirin component)
1 capsule (propoxyphene HCl 65 mg / aspirin 650 mg) orally every 4 hours as needed for pain, not to exceed 6 capsules per day.
1-2 capsules (propoxyphene napsylate 100 mg / aspirin 325 mg per capsule) orally every 4 hours as needed for pain; maximum 6 capsules per day.
None Documented
None Documented
Propoxyphene terminal half-life is 6–12 hours (mean 8 h) in healthy adults; prolonged in hepatic impairment or elderly due to reduced metabolism. Aspirin half-life is 15–20 minutes due to rapid hydrolysis to salicylate.
Propoxyphene: terminal elimination half-life is 6-12 hours in adults with normal renal function; norpropoxyphene has a longer half-life (30-36 hours). Aspirin (as salicylate): half-life is dose-dependent, ranging from 2-3 hours at low doses to 15-30 hours at anti-inflammatory doses (300-600 mg in Darvon-N W/ASA).
Propoxyphene undergoes hepatic metabolism via N-demethylation to norpropoxyphene (active metabolite); both are primarily excreted renally. Aspirin is rapidly hydrolyzed to salicylate, which is metabolized by conjugation and oxidation, with renal excretion.
Propoxyphene is metabolized via CYP3A4 to norpropoxyphene (active metabolite). Aspirin is hydrolyzed to salicylic acid and conjugated with glycine (salicyluric acid) and glucuronic acid.
Renal elimination of propoxyphene and its metabolites accounts for ~70% of a dose, with ~20% excreted unchanged in urine; biliary/fecal elimination accounts for ~10%; aspirin is renally excreted as salicylate and its conjugates.
Renal: propoxyphene and its metabolites (norpropoxyphene) are primarily eliminated via kidneys, with ~20-25% excreted unchanged; fecal: minor; biliary: some enterohepatic recirculation occurs, but exact % are not well quantified for the combination product. Aspirin is hydrolyzed to salicylate, which is excreted renally (75% as salicyluric acid, 10% as salicylic acid, 10% as glucuronide conjugates, and minor amounts as gentisic acid).
Propoxyphene is 70–80% bound to albumin; aspirin is 50–80% bound to albumin (dose-dependent due to saturable binding).
Propoxyphene: ~80% bound to albumin; norpropoxyphene: ~90% bound. Aspirin: 50-80% bound to albumin (dose-dependent); salicylate: 50-90% bound.
Propoxyphene Vd is 6–10 L/kg, indicating extensive tissue distribution; aspirin Vd is 0.15–0.2 L/kg, primarily in plasma and extracellular fluid.
Propoxyphene: 10-16 L/kg (large Vd indicating extensive tissue distribution); norpropoxyphene: similar. Aspirin: 0.1-0.2 L/kg (limited distribution as salicylate is highly protein-bound).
Propoxyphene: 30–70% oral bioavailability due to first-pass metabolism; aspirin: 50–70% oral bioavailability (first-pass hydrolysis to salicylate).
Oral propoxyphene: 30-70% due to first-pass metabolism (higher for propoxyphene napsylate than hydrochloride). Aspirin: 50-75% (but rapidly hydrolyzed to salicylate, which has near-complete bioavailability after oral administration).
Contraindicated in severe renal impairment (eGFR <30 mL/min/1.73m²). For moderate impairment (eGFR 30-59), reduce dose to 1 capsule every 6 hours. No adjustment needed for mild impairment (eGFR ≥60).
GFR 30-50 mL/min: avoid use; GFR <30 mL/min: contraindicated due to propoxyphene accumulation. Aspirin component may further impair renal function.
Contraindicated in Child-Pugh class C. For Child-Pugh class B, maximum 2 capsules per day. For Child-Pugh class A, no adjustment required but monitor closely.
Child-Pugh Class A: no adjustment; Class B: reduce dose by 50% or extend interval; Class C: contraindicated due to increased propoxyphene toxicity and bleeding risk from aspirin.
Not recommended for children under 12 years. For children 12-18 years: 1 capsule (propoxyphene 65 mg/aspirin 650 mg) every 4 hours as needed, maximum 6 capsules/day. Weight-based dosing not established due to fixed combination.
Not recommended for pediatric use due to risk of Reye's syndrome (aspirin) and propoxyphene toxicity.
Initiate with 1 capsule every 6 hours. Maximum 4 capsules per day due to increased sensitivity and risk of CNS depression and renal impairment. Avoid in patients >75 years or those with frailty.
Initiate with half the adult dose (maximum 1 capsule every 6 hours) due to increased sensitivity, reduced clearance, and higher risk of CNS and GI adverse effects.
Propoxyphene is associated with a risk of fatal respiratory depression, especially in overdose or when combined with CNS depressants. Use with caution in elderly, debilitated, or patients with respiratory compromise.
Propoxyphene has been withdrawn from the US market due to risk of fatal cardiac toxicity (QT prolongation, Torsades de Pointes). FDA boxed warning prior to withdrawal included risk of respiratory depression, abuse potential, and fatal overdose.
Risk of respiratory depression; hepatotoxicity with chronic high doses; GI bleeding, ulceration, and perforation with aspirin; renal toxicity; hypersensitivity reactions; use in elderly, renal/hepatic impairment, or history of alcohol abuse.
Risk of respiratory depression, QT prolongation, cardiac arrhythmias, abuse potential, hepatotoxicity (overdose), aspirin hypersensitivity, bleeding risk (aspirin), Reye's syndrome (in children with viral illness).
Hypersensitivity to propoxyphene, aspirin, or NSAIDs; severe respiratory depression; acute or severe asthma; GI bleeding; history of peptic ulcer disease; hemophilia; children with viral infections (Reye's syndrome); concurrent MAOIs or alcohol.
Hypersensitivity to propoxyphene or aspirin, significant respiratory depression, acute or severe bronchial asthma, known QT prolongation, children with viral illness (Reye's syndrome risk), third trimester of pregnancy (aspirin), history of aspirin-induced asthma or nasal polyps.
Data Pending Review
Data Pending Review
Avoid alcohol. Aspirin component may cause gastrointestinal irritation; take with food or milk to reduce stomach upset. Avoid foods high in tyramine (e.g., aged cheese, processed meats) as propoxyphene may have weak MAOI activity? Not established but caution advised.
Avoid alcohol. Aspirin may cause gastrointestinal irritation; take with food or milk to reduce stomach upset. Avoid foods high in vitamin K (e.g., leafy greens) if on anticoagulants, as aspirin may enhance anticoagulant effect.
First trimester: Aspirin component associated with increased risk of neural tube defects and gastroschisis. Propoxyphene not associated with major malformations but data limited. Second trimester: Aspirin risk increases for fetal intracranial hemorrhage with chronic use. Third trimester: Aspirin may cause premature closure of ductus arteriosus, oligohydramnios, and increased perinatal hemorrhage. Propoxyphene may cause neonatal withdrawal syndrome.
First trimester: ASA associated with neural tube defects, gastroschisis; propoxyphene limited data, possible cardiac defects. Second trimester: ASA may reduce amniotic fluid; propoxyphene risk not established. Third trimester: ASA increases risk of premature ductus arteriosus closure, oligohydramnios, neonatal hemorrhage; propoxyphene may cause neonatal respiratory depression, withdrawal. Overall risk considered moderate; avoid in third trimester.
Aspirin enters breast milk in low amounts; M/P ratio ~0.1. Propoxyphene M/P ratio ~0.5. Both can accumulate in neonates with repeated dosing. Potential for infant sedation, respiratory depression, and Reye's syndrome. Contraindicated in breastfeeding due to risks.
Propoxyphene excreted into breast milk; M/P ratio approximate 0.5; ASA excreted in low amounts. Potential for neonatal opioid effects (respiratory depression, sedation) and Reye's syndrome with ASA. Contraindicated in breastfeeding due to risks; alternative agents recommended.
No specific dose adjustments in pregnancy. However, because of altered pharmacokinetics (increased volume of distribution, renal clearance), clinicians should titrate to effect and monitor for toxicity. Avoid high-dose aspirin in third trimester due to fetal risks. Propoxyphene clearance may be increased in pregnancy, but no standard dose change recommended; use minimal effective dose.
No established safe dosage; contraindicated in pregnancy. Increased renal clearance during pregnancy may decrease propoxyphene levels but risk outweighs benefit. Avoid use; no dose adjustment recommended.
Category C
Category C
Darvon with ASA contains propoxyphene and aspirin. Propoxyphene has been withdrawn from the US market due to cardiotoxicity (QT prolongation, risk of fatal arrhythmias). Use is not recommended; consider alternatives. Aspirin component increases bleeding risk, especially with concurrent anticoagulants. Avoid in children with viral illness due to Reye's syndrome risk.
Darvon-N with ASA contains propoxyphene napsylate (a weak opioid) and aspirin. Due to propoxyphene's cardiac toxicity (QT prolongation, risk of fatal arrhythmias) and limited efficacy, it was withdrawn from the US market in 2010. Avoid use; consider alternative analgesics. If encountered, monitor ECG for QTc prolongation, avoid in patients with electrolyte abnormalities, and do not exceed recommended doses. Aspirin component requires caution in bleeding risk, peptic ulcer disease, and children with viral illness (Reye's syndrome).
Do not take more than prescribed as overdose can cause serious heart problems or death.Avoid alcohol while taking this medication as it increases risk of liver damage and bleeding.Aspirin may increase risk of bleeding; report unusual bruising or bleeding to your doctor.If you have asthma, nasal polyps, or allergies, aspirin may cause severe allergic reactions.Do not use in children or teenagers with chickenpox or flu-like symptoms due to risk of Reye's syndrome.This medicine may cause drowsiness or dizziness; avoid driving until you know how it affects you.
This medication contains propoxyphene, which has been removed from the US market due to serious heart risks.Do not take more than prescribed; overdose can cause life-threatening heart rhythm problems.Avoid alcohol and other central nervous system depressants (e.g., benzodiazepines, other opioids) due to additive sedation and respiratory depression.Aspirin may increase bleeding risk; stop use 1 week before surgery and avoid in children with chickenpox or flu-like symptoms.Do not use during pregnancy, especially third trimester, due to risk of premature closure of ductus arteriosus and neonatal bleeding.Store securely out of reach of children; dispose of unused medication properly.