Comparative Pharmacology
Head-to-head clinical analysis: PHENAPHEN W CODEINE NO 2 versus WESTADONE.
Peer-Reviewed Evidence
Head-to-head clinical analysis: PHENAPHEN W CODEINE NO 2 versus WESTADONE.
PHENAPHEN W/ CODEINE NO. 2 vs WESTADONE
Comparing the clinical profiles, pharmacokinetic behaviors, and safety indices of these two therapeutic agents.
Codeine is an opioid agonist with affinity for mu-opioid receptors, producing analgesia, cough suppression, and sedation. Acetaminophen is a centrally acting analgesic and antipyretic with unclear mechanism, possibly involving COX-2 inhibition and cannabinoid receptor activation.
Mu-opioid receptor agonist; also acts as an NMDA receptor antagonist and inhibits serotonin and norepinephrine reuptake.
1-2 tablets (codeine 15-30 mg, acetaminophen 325-650 mg) 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
Phenacetin: terminal half-life ~0.5-2 hours (rapidly eliminated; active metabolite APAP has half-life ~2-3 hours). Codeine: terminal half-life ~2.5-4 hours (increased in CYP2D6 poor metabolizers). Acetaminophen: terminal half-life ~1.5-3 hours (prolonged in hepatic impairment or overdose). Clinical context: half-lives are shortened with chronic use due to autoinduction (phenacetin) and unchanged with therapeutic doses.
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.
Phenacetin (active metabolite): renal elimination of conjugated metabolites, primarily as sulfate and glucuronide conjugates; ~60% renal. Codeine: ~90% renal, with 5-15% as free codeine, 10% as norcodeine, and 40-70% as conjugated morphine and norcodeine; ~10% fecal. Apap (acetaminophen): renal elimination of conjugated metabolites, with ~85% excreted in urine as sulfate and glucuronide conjugates, ~5% as unchanged drug, and <5% as cysteine/mercapturate 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