PROPOXYPHENE HYDROCHLORIDE AND ACETAMINOPHEN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for PROPOXYPHENE HYDROCHLORIDE AND ACETAMINOPHEN (PROPOXYPHENE HYDROCHLORIDE AND ACETAMINOPHEN).
Propoxyphene is a mu-opioid receptor agonist; acetaminophen inhibits cyclooxygenase (COX) and modulates central pain pathways.
| Metabolism | Propoxyphene: hepatic via CYP3A4 and CYP2D6 to norpropoxyphene (active); acetaminophen: hepatic via conjugation (glucuronidation, sulfation) and CYP2E1. |
| Excretion | Renal: Propoxyphene ~20-25% as unchanged drug and metabolites; Acetaminophen ~85-90% as glucuronide and sulfate conjugates, <5% unchanged. Fecal: Minimal for both. |
| Half-life | Propoxyphene: 6-12 h (prolonged in hepatic disease); Norpropoxyphene (active metabolite): 30-36 h (accumulation risk). Acetaminophen: 2-3 h (prolonged in hepatic disease). |
| Protein binding | Propoxyphene: ~80% bound to albumin; Acetaminophen: 10-25% bound to albumin at therapeutic concentrations. |
| Volume of Distribution | Propoxyphene: 12-26 L/kg (large, extensive tissue distribution; clinical meaning: high CNS penetration). Acetaminophen: 0.9-1.0 L/kg (clinical meaning: uniform distribution, limited tissue binding). |
| Bioavailability | Oral: Propoxyphene ~30-70% due to extensive first-pass metabolism; Acetaminophen ~85-90%. |
| Onset of Action | Oral: Propoxyphene effect within 30-60 min; Acetaminophen antipyretic effect within 30 min. |
| Duration of Action | Propoxyphene: 4-6 h (analgesic); Acetaminophen: 4-6 h (antipyretic/analgesic). Note: Norpropoxyphene may prolong toxicity risk. |
One tablet (propoxyphene HCl 65 mg/acetaminophen 650 mg) orally every 4 hours as needed for pain; maximum: 6 tablets per day.
| Dosage form | TABLET |
| Renal impairment | Not recommended in severe renal impairment (CrCl <30 mL/min). For moderate impairment (CrCl 30-50 mL/min), reduce frequency to every 6-8 hours; use with caution. |
| Liver impairment | Contraindicated in severe hepatic impairment (Child-Pugh C). For Child-Pugh A or B, reduce dose by 50% and monitor hepatic function; maximum duration limited. |
| Pediatric use | Not recommended for pediatric use due to risk of respiratory depression and propoxyphene toxicity; safety and efficacy not established. |
| Geriatric use | Initiate with lower doses (e.g., half tablet) and increase cautiously; avoid in elderly with renal or hepatic impairment; monitor for CNS and respiratory effects. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for PROPOXYPHENE HYDROCHLORIDE AND ACETAMINOPHEN (PROPOXYPHENE HYDROCHLORIDE AND ACETAMINOPHEN).
| Breastfeeding | Propoxyphene is excreted into breast milk in low concentrations (M/P ratio approximately 0.5); however, the combination with acetaminophen may pose risks of sedation and respiratory depression in the infant. Acetaminophen is considered compatible with breastfeeding. Use with caution, monitor infant for drowsiness and feeding difficulties. |
| Teratogenic Risk | Propoxyphene is contraindicated in pregnancy due to risk of neonatal opioid withdrawal syndrome and respiratory depression. Acetaminophen is generally considered safe in pregnancy at therapeutic doses. First trimester: Propoxyphene may increase risk of congenital malformations, though data are limited. Second/third trimester: Prolonged use may cause neonatal opioid withdrawal; high doses near term may cause respiratory depression in the neonate. |
■ FDA Black Box Warning
Risk of respiratory depression, addiction, abuse, and misuse; concomitant use with benzodiazepines or CNS depressants may cause profound sedation, respiratory depression, coma, and death.
| Serious Effects |
["Hypersensitivity to propoxyphene or acetaminophen","Significant respiratory depression","Acute or severe bronchial asthma","Paralytic ileus","Concurrent alcohol use (risk of hepatotoxicity)","MAO inhibitor use within 14 days","Known prolonged QT interval or on QT-prolonging drugs"]
| Precautions | ["Respiratory depression risk","Abuse and dependence potential","CNS depression with alcohol or other drugs","Hepatotoxicity from acetaminophen overdose","QT prolongation with high doses","Neonatal opioid withdrawal syndrome with prolonged use during pregnancy"] |
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| Fetal Monitoring | Monitor maternal respiratory status, sedation level, and signs of opioid toxicity. For the fetus, monitor for growth restrictions, preterm labor, and non-stress testing in cases of prolonged use. Neonates exposed in utero require monitoring for opioid withdrawal (e.g., Finnegan scoring). |
| Fertility Effects | Propoxyphene may impair fertility in both males and females by disrupting hormonal regulation and affecting sperm or ovum function. Acetaminophen at high doses may also impact fertility; data are limited. Discontinuation may restore fertility. |