Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
CODEPREX vs PROMETH W/ DEXTROMETHORPHAN
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Codeine is a prodrug converted to morphine via CYP2D6; morphine acts as a mu-opioid receptor agonist, while homatropine is an anticholinergic that reduces respiratory secretions.
Promethazine is a phenothiazine derivative that acts as a central H1 receptor antagonist with anticholinergic, antiemetic, and sedative properties. Dextromethorphan is a non-competitive NMDA receptor antagonist and sigma-1 receptor agonist that suppresses cough by acting on the cough center in the medulla oblongata.
Cough suppression (FDA-approved)
Symptomatic relief of cough associated with upper respiratory tract infections,Allergic rhinitis,Motion sickness,Nausea and vomiting,Sedation
Adults: 1 tablet (containing 5 mg hydrocodone and 325 mg acetaminophen) orally every 4-6 hours as needed for pain; maximum 6 tablets per day.
Adults: 10 m L (containing promethazine 6.25 mg and dextromethorphan 15 mg) orally every 4-6 hours, not to exceed 4 doses (40 m L) in 24 hours.
4-6 hours (prolonged to 10-12 hours in hepatic impairment)
Promethazine: terminal elimination half-life 10-14 hours (range 5-30 hours). Clinical context: prolonged half-life in elderly or hepatic impairment; requires dose adjustment in severe liver disease. Dextromethorphan: 3-6 hours for extensive CYP2D6 metabolizers; 24-48 hours in poor metabolizers.
Codeine undergoes O-demethylation via CYP2D6 to morphine; also N-demethylation to norcodeine via CYP3A4; homatropine is minimally metabolized.
Promethazine is extensively metabolized in the liver via sulfation (primary) and CYP2D6-mediated N-demethylation. Dextromethorphan is metabolized by CYP2D6 to dextrorphan, an active metabolite.
Renal: 60% as unchanged drug; Hepatic metabolism: 30% (inactive metabolites); Fecal: 10%
Promethazine is primarily excreted via renal elimination (70-80% as metabolites, <1% unchanged) and fecal/biliary elimination (20-30%). Dextromethorphan is extensively metabolized; renal excretion accounts for ~45% as dextrorphan and other metabolites, with minimal unchanged drug (<1%).
92% (primarily to albumin)
Promethazine: 93% bound primarily to albumin. Dextromethorphan: 60-70% bound to albumin and alpha-1-acid glycoprotein.
1.5-2.0 L/kg (extensive tissue distribution)
Promethazine: 7-9 L/kg, indicating extensive tissue distribution. Dextromethorphan: 5-7 L/kg, with high tissue binding. Clinical meaning: large Vd suggests poor dialyzability and prolonged washout.
Oral: 70-80% (first-pass metabolism reduces from 100% IV)
Promethazine: oral 25% (extensive first-pass metabolism), intramuscular 100%, rectal 70-80%. Dextromethorphan: oral 11-60% (dependent on CYP2D6 metabolism), intramuscular not available.
Hydrocodone: GFR 30-80 m L/min: no adjustment; GFR 10-29 m L/min: reduce dose by 50% or extend interval to every 8-12 hours; GFR <10 m L/min: use with caution, consider alternative. Acetaminophen: GFR <10 m L/min: extend dosing interval to every 8 hours.
GFR ≥ 30 m L/min: no adjustment. GFR < 30 m L/min: avoid use due to risk of CNS depression and accumulation of metabolites.
Child-Pugh Class A: no adjustment; Class B: reduce dose by 50% and extend interval to every 8 hours; Class C: contraindicated due to acetaminophen toxicity risk and impaired hydrocodone metabolism.
Child-Pugh A (mild): no adjustment. Child-Pugh B (moderate): reduce dose by 50% or prolong dosing interval. Child-Pugh C (severe): avoid use.
Not recommended for pediatric use (no safety and efficacy data established).
Children 6-11 years: 5 m L (half the adult dose) every 4-6 hours, max 4 doses/24h. Children 2-5 years: 2.5 m L every 4-6 hours, max 4 doses/24h. Not recommended under 2 years due to risk of respiratory depression.
Start at low end of dosing range (1 tablet every 6 hours) due to increased sensitivity, reduced renal function, and risk of cognitive impairment.
Initiate at lowest effective dose (e.g., 5 m L every 6-8 hours). Monitor for sedation, confusion, and anticholinergic effects. Avoid in elderly with dementia or high fall risk.
Risk of respiratory depression, especially in children; contraindicated for postoperative pain management in children after tonsillectomy/adenoidectomy; contraindicated in children <12 years, and in children <18 years with risk factors for respiratory depression.
Promethazine should not be used in children younger than 2 years of age due to the risk of respiratory depression that can be fatal. Use with caution in children older than 2 years.
Respiratory depression; ultra-rapid metabolizers of CYP2D6 at risk of morphine toxicity; use in breastfeeding may cause infant opioid toxicity; anticholinergic effects of homatropine; risk of abuse and dependence; CNS depression with other depressants.
Respiratory depression, especially in children and elderly,CNS depression and impaired alertness,Anticholinergic effects (e.g., dry mouth, urinary retention),Extrapyramidal symptoms with high doses,Neuroleptic malignant syndrome (rare),Photo-sensitivity,Seizure threshold lowering,Increased risk of hypotension,Hepatic impairment may require dose adjustment
Hypersensitivity to codeine or homatropine; respiratory depression; acute or severe bronchial asthma; GI obstruction; paralytic ileus; children <12 years; children <18 years with tonsillectomy/adenoidectomy; use with MAOIs or within 14 days; breastfeeding women with CYP2D6 ultrarapid metabolism.
Hypersensitivity to promethazine, dextromethorphan, or any component,Children younger than 2 years,Comatose states,Use of MAO inhibitors within 14 days,Lower respiratory tract symptoms including asthma,Severe CNS depression,Angle-closure glaucoma (relative),Prostatic hypertrophy (relative),Seizure disorders (caution)
Grapefruit juice may inhibit CYP2D6 and reduce codeine conversion to morphine, potentially decreasing efficacy. High-fat meals may delay absorption of codeine. Avoid alcohol.
Avoid grapefruit juice as it may increase dextromethorphan levels. No significant food interactions with promethazine.
Based on available data, codeine is pregnancy category C. First trimester: Avoid due to possible association with congenital malformations (e.g., cardiovascular defects) from retrospective studies, though risk is low. Second and third trimesters: Risk of neonatal respiratory depression if used near term; chronic use may lead to neonatal withdrawal syndrome. Avoid if possible.
First trimester: Limited human data; animal studies with promethazine show no consistent teratogenicity. Dextromethorphan is not teratogenic in animal studies. Second/third trimester: Use of promethazine near term may cause respiratory depression or extrapyramidal symptoms in neonates. Dextromethorphan has minimal fetal risk. Overall, FDA Pregnancy Category C for promethazine; dextromethorphan is Category A (no evidence of risk).
Codeine is excreted into breast milk. M/P ratio is approximately 2.5. Use with caution due to risk of infant CNS depression, especially in mothers who are CYP2D6 ultra-rapid metabolizers. AAP recommends lowest effective dose for shortest duration; monitor infant for drowsiness, difficulty breathing, or poor feeding.
Promethazine is excreted into breast milk in small amounts; M/P ratio not well established. Dextromethorphan is excreted in breast milk but levels are low. Use with caution; monitor infant for drowsiness or irritability.
No standard dose adjustment required, but avoid use in third trimester due to risk of neonatal respiratory depression. If used, use lowest effective dose for shortest duration. Monitor for signs of maternal respiratory depression; consider reduced dose in patients with decreased respiratory reserve.
No specific dosing adjustments required for pregnancy; however, use lowest effective dose and shortest duration. Consider increased renal clearance of dextromethorphan in pregnancy, but no dose adjustment is established.
CODEPREX (codeine/guaifenesin) is a combination antitussive/expectorant. Codeine is a prodrug metabolized by CYP2D6 to morphine; ultra-rapid metabolizers risk toxicity. Avoid in children <18 years due to respiratory depression risk. Use with caution in patients with COPD or respiratory insufficiency. Constipation is common; consider prophylactic laxatives.
Promethazine (a phenothiazine antiemetic/antihistamine) combined with dextromethorphan (an NMDA receptor antagonist/antitussive) is used for cough and cold symptoms. Promethazine can cause respiratory depression, especially in children, and is contraindicated under age 2. Dextromethorphan at high doses can cause dissociative effects; avoid concurrent use with MAOIs or serotonergic drugs. This combination has significant anticholinergic effects (dry mouth, urinary retention, constipation). Use cautiously in patients with asthma, COPD, or sleep apnea due to respiratory depression risk.
Do not exceed recommended dose; may cause drowsiness, avoid driving or operating machinery until you know how this medication affects you.,Avoid alcohol and other CNS depressants as they increase sedation and respiratory depression risk.,Do not use in children under 18 years of age due to risk of serious breathing problems.,Contact your doctor if cough persists for more than 7 days or is accompanied by fever, rash, or persistent headache.,May cause constipation; increase fluid and fiber intake, and consider a stool softener if needed.,Store at room temperature away from moisture and heat.
Do not use in children younger than 2 years due to risk of serious breathing problems.,May cause drowsiness or dizziness; avoid driving or operating heavy machinery until you know how you react.,Avoid alcohol and other CNS depressants (e.g., benzodiazepines, opioids) as they increase sedation and respiratory depression risk.,Do not take with MAO inhibitors or within 14 days of stopping them.,Increase fluid intake to help loosen mucus.,Stop use and seek medical attention if cough persists > 1 week, is accompanied by fever or rash, or if excessive sedation occurs.
No interactions on record
"The combination of dextromethorphan, a centrally acting antitussive with NMDA receptor antagonist and sigma-1 receptor agonist properties, and aceprometazine, a phenothiazine neuroleptic with strong antihistaminergic and moderate anticholinergic and antidopaminergic effects, can result in additive central nervous system depression. This interaction may lead to excessive sedation, respiratory depression, impaired psychomotor function, and an increased risk of falls or cognitive impairment, particularly in elderly or debilitated patients. Concurrent use may also lower the seizure threshold, especially in patients with predisposing factors."
"Dextromethorphan, a serotonergic agent metabolized by CYP2D6, when combined with cariprazine, a dopamine D3/D2 receptor partial agonist, may increase the risk of serotonin syndrome due to additive serotonergic effects. Cariprazine can inhibit CYP2D6, reducing dextromethorphan clearance and elevating its plasma concentration, leading to enhanced serotonin activity. Clinically, patients may present with altered mental status, autonomic instability, and neuromuscular abnormalities."
"Dextromethorphan inhibits CYP2B6 and CYP2C9, which are involved in valproic acid metabolism. This results in decreased valproic acid clearance, potentially elevating valproic acid serum concentrations and increasing the risk of dose-dependent adverse effects such as hepatotoxicity, thrombocytopenia, and sedation. Concurrent use requires dose adjustment and close monitoring for signs of valproate toxicity."
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about CODEPREX vs PROMETH W/ DEXTROMETHORPHAN, answered by our medical review team.
CODEPREX is a Antitussive Combination that works by Codeine is a prodrug converted to morphine via CYP2D6; morphine acts as a mu-opioid receptor agonist, while homatropine is an anticholinergic that reduces respiratory secretions.. PROMETH W/ DEXTROMETHORPHAN is a Antihistamine-antitussive combination that works by Promethazine is a phenothiazine derivative that acts as a central H1 receptor antagonist with anticholinergic, antiemetic, and sedative properties. Dextromethorphan is a non-competitive NMDA receptor antagonist and sigma-1 receptor agonist that suppresses cough by acting on the cough center in the medulla oblongata.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between CODEPREX and PROMETH W/ DEXTROMETHORPHAN depend on the specific clinical indication. These are agents from distinct pharmacological classes and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of CODEPREX is: Adults: 1 tablet (containing 5 mg hydrocodone and 325 mg acetaminophen) orally every 4-6 hours as needed for pain; maximum 6 tablets per day.. The standard adult dose of PROMETH W/ DEXTROMETHORPHAN is: Adults: 10 m L (containing promethazine 6.25 mg and dextromethorphan 15 mg) orally every 4-6 hours, not to exceed 4 doses (40 m L) in 24 hours.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between CODEPREX and PROMETH W/ DEXTROMETHORPHAN in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. CODEPREX is classified as Category C. Based on available data, codeine is pregnancy category C. First trimester: Avoid due to possible association with congenital malformations (e.g., cardiovascular defects) from retro. PROMETH W/ DEXTROMETHORPHAN is classified as Category C. First trimester: Limited human data; animal studies with promethazine show no consistent teratogenicity. Dextromethorphan is not teratogenic in animal studies. Second/third trimest. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.