Comparative Pharmacology
Head-to-head clinical analysis: PHERAZINE W CODEINE versus WESTADONE.
Peer-Reviewed Evidence
Head-to-head clinical analysis: PHERAZINE W CODEINE versus WESTADONE.
PHERAZINE W/ CODEINE vs WESTADONE
Comparing the clinical profiles, pharmacokinetic behaviors, and safety indices of these two therapeutic agents.
Promethazine is a phenothiazine derivative that acts as a histamine H1 receptor antagonist, antiemetic, and sedative. It also exerts anticholinergic and antidopaminergic effects, particularly at D2 receptors. Codeine is an opioid agonist primarily at mu-opioid receptors, leading to analgesia and antitussive effects. The combination enhances sedation and antiemetic action.
Mu-opioid receptor agonist; also acts as an NMDA receptor antagonist and inhibits serotonin and norepinephrine reuptake.
One tablet (promethazine 6.25 mg / codeine 10 mg) orally every 4-6 hours as needed; maximum 4 tablets in 24 hours.
Oral: 2.5-10 mg every 4-6 hours as needed for pain; maximum 40 mg per day.
None Documented
None Documented
Promethazine: 9-16 hours in adults; codeine: 2.5-3.5 hours; morphine: 1.5-2 hours. Clinical context: The half-life of codeine is shorter, but its active metabolite morphine contributes to analgesia. Accumulation may occur with repeated dosing.
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 (50-70% as unchanged promethazine and metabolites; codeine and its metabolites, primarily morphine and codeine-6-glucuronide, are excreted renally). Biliary/fecal elimination accounts for less than 10%.
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