Comparative Pharmacology
Head-to-head clinical analysis: PROMETH VC W CODEINE versus WESTADONE.
Peer-Reviewed Evidence
Head-to-head clinical analysis: PROMETH VC W CODEINE versus WESTADONE.
PROMETH VC W/ CODEINE vs WESTADONE
Comparing the clinical profiles, pharmacokinetic behaviors, and safety indices of these two therapeutic agents.
Promethazine is a phenothiazine derivative with antihistaminic, sedative, antiemetic, and anticholinergic effects. Codeine is an opioid agonist; its analgesic and antitussive effects are mediated via mu-opioid receptors.
Mu-opioid receptor agonist; also acts as an NMDA receptor antagonist and inhibits serotonin and norepinephrine reuptake.
10 mL (5 mg codeine, 6.25 mg promethazine) orally every 4-6 hours as needed, not to exceed 60 mg codeine 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: terminal elimination half-life is 2.5-4 hours in adults. Promethazine: terminal elimination half-life is 9-16 hours, with a mean of 12 hours.
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.
Codeine and its metabolites are primarily excreted renally. Approximately 90% of a dose is excreted in the urine within 24 hours, with 10-15% as unchanged codeine, 40-60% as codeine-6-glucuronide, 5-15% as morphine, and 5-10% as norcodeine. Promethazine is extensively metabolized in the liver and excreted in urine and feces; about 70-80% appears in urine as metabolites and unchanged drug (less than 1% unchanged), with 20-30% in feces via biliary elimination.
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