Comparative Pharmacology
Head-to-head clinical analysis: PHENAPHEN W CODEINE NO 4 versus WESTADONE.
Peer-Reviewed Evidence
Head-to-head clinical analysis: PHENAPHEN W CODEINE NO 4 versus WESTADONE.
PHENAPHEN W/ CODEINE NO. 4 vs WESTADONE
Comparing the clinical profiles, pharmacokinetic behaviors, and safety indices of these two therapeutic agents.
Phenaphen w/ Codeine No. 4 contains acetaminophen and codeine. Acetaminophen inhibits prostaglandin synthesis in the CNS, reducing pain and fever. Codeine, an opioid prodrug, is converted to morphine via CYP2D6 and binds to mu-opioid receptors, inhibiting ascending pain pathways.
Mu-opioid receptor agonist; also acts as an NMDA receptor antagonist and inhibits serotonin and norepinephrine reuptake.
1-2 tablets (300-600 mg acetaminophen / 30-60 mg codeine phosphate) orally every 4 hours as needed for pain; maximum 12 tablets per day.
Oral: 2.5-10 mg every 4-6 hours as needed for pain; maximum 40 mg per day.
None Documented
None Documented
Codeine: 2.5-3.5 h; morphine: 2-4 h; clinically, analgesia correlates with morphine levels
Terminal elimination half-life: 15-60 hours (mean ~24 hours). Clinical context: Prolonged half-life supports once-daily dosing in opioid maintenance; accumulation occurs with repeated dosing due to long half-life.
Renal: 90-100% as codeine and metabolites (codeine: 5-15%, morphine: 10%, norcodeine: 10%, morphine-3-glucuronide: 50%, morphine-6-glucuronide: <5%); biliary/fecal: minimal (<5%)
Primarily renal (40-50% as unchanged methadone and its metabolites, 15-20% as metadone-N-oxide), biliary/fecal (5-10%).
Category D/X
Category C
Opioid Agonist
Opioid Agonist