Comparative Pharmacology
Head-to-head clinical analysis: PHENAPHEN 650 W CODEINE versus WESTADONE.
Peer-Reviewed Evidence
Head-to-head clinical analysis: PHENAPHEN 650 W CODEINE versus WESTADONE.
PHENAPHEN-650 W/ CODEINE vs WESTADONE
Comparing the clinical profiles, pharmacokinetic behaviors, and safety indices of these two therapeutic agents.
Acetaminophen: Weak COX-1 and COX-2 inhibitor in CNS, antipyretic via hypothalamic heat-regulating center. Codeine: Prodrug converted to morphine; mu-opioid receptor agonist.
Mu-opioid receptor agonist; also acts as an NMDA receptor antagonist and inhibits serotonin and norepinephrine reuptake.
Acetaminophen 650 mg and codeine 60 mg orally every 4 hours as needed for pain; maximum acetaminophen 3 g/day.
Oral: 2.5-10 mg every 4-6 hours as needed for pain; maximum 40 mg per day.
None Documented
None Documented
Acetaminophen: 2-3 hours (normal liver function); prolonged in liver disease (up to 5-10 hours) or overdose. Codeine: 2.5-3.5 hours; active metabolite morphine ~2 hours. Clinical context: half-life affects dosing interval; accumulation in hepatic or renal impairment.
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.
Acetaminophen: renal excretion of conjugates (glucuronide ~55%, sulfate ~30%, cysteine/mercapturate ~4%), with <5% unchanged. Codeine: renal excretion as codeine (~10%), norcodeine (~10%), morphine (~10%), and their conjugates; total 70-90% in urine as glucuronide conjugates.
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