Comparative Pharmacology
Head-to-head clinical analysis: ARYMO ER versus DARVON.
Peer-Reviewed Evidence
Head-to-head clinical analysis: ARYMO ER versus DARVON.
ARYMO ER vs DARVON
Comparing the clinical profiles, pharmacokinetic behaviors, and safety indices of these two therapeutic agents.
ARYMO ER (morphine sulfate) is a full opioid agonist that binds to mu-opioid receptors in the central nervous system (CNS), inhibiting ascending pain pathways and altering pain perception. It also activates descending inhibitory pathways.
Propoxyphene is a mu-opioid receptor agonist that inhibits ascending pain pathways by binding to opioid receptors in the CNS, altering pain perception. It also has weak local anesthetic effects.
15 mg to 30 mg orally every 12 hours; titrate to effect; maximum 60 mg per dose.
Propoxyphene hydrochloride (Darvon) for moderate to severe pain: 65 mg orally every 4 hours as needed; maximum 390 mg/day.
None Documented
None Documented
Terminal elimination half-life is approximately 11–13 hours in healthy adults. This extended half-life compared to immediate-release morphine (2–4 hours) allows for once-daily dosing. In elderly or hepatic/renal impairment, half-life may be prolonged up to 22 hours.
6-12 hours (parent drug); norpropoxyphene half-life 30-36 hours, accumulates with repeated dosing, increasing risk of toxicity.
Primarily renal (90%), with approximately 10% excreted unchanged in urine; the remainder as glucuronide conjugates (morphine-3-glucuronide, morphine-6-glucuronide) and minor metabolites. Biliary/fecal excretion accounts for <10%.
Primarily hepatic metabolism to norpropoxyphene, then renal excretion of metabolites; <20% excreted unchanged in urine; minor biliary/fecal elimination.
Category C
Category C
Opioid Analgesic
Opioid Analgesic