Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
PROMETH W/ DEXTROMETHORPHAN vs MUCINEX DM
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
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.
Guaifenesin increases respiratory tract fluid secretion to reduce mucus viscosity; dextromethorphan acts on sigma-1 receptors and NMDA receptor antagonism to suppress cough reflex.
Symptomatic relief of cough associated with upper respiratory tract infections,Allergic rhinitis,Motion sickness,Nausea and vomiting,Sedation
Temporary relief of cough due to minor throat and bronchial irritation,Temporary relief of chest congestion and mucus buildup
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.
One tablet (guaifenesin 600 mg / dextromethorphan HBr 30 mg) orally every 12 hours, not to exceed 2 tablets in 24 hours.
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.
Guaifenesin: 1-3 hours. Dextromethorphan: 3-30 hours depending on CYP2D6 phenotype; extensive metabolizers 3-8 hours, poor metabolizers 15-30 hours.
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.
Guaifenesin undergoes hepatic metabolism via oxidation and conjugation; dextromethorphan is metabolized by CYP2D6 to dextrorphan, an active metabolite.
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%).
Guaifenesin: renal (primarily as inactive metabolites, <1% unchanged). Dextromethorphan: renal (as unchanged drug and metabolites, including dextrorphan). Approximately 80% eliminated in urine as metabolites.
Promethazine: 93% bound primarily to albumin. Dextromethorphan: 60-70% bound to albumin and alpha-1-acid glycoprotein.
Guaifenesin: approximately 30% to albumin. Dextromethorphan: approximately 50% to albumin and alpha-1-acid glycoprotein.
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.
Guaifenesin: 0.8-1.5 L/kg. Dextromethorphan: 5-10 L/kg (extensive tissue binding).
Promethazine: oral 25% (extensive first-pass metabolism), intramuscular 100%, rectal 70-80%. Dextromethorphan: oral 11-60% (dependent on CYP2D6 metabolism), intramuscular not available.
Oral: Guaifenesin ~100% (tablet/syrup). Dextromethorphan ~11% (extensive first-pass metabolism; varies with CYP2D6 phenotype).
GFR ≥ 30 m L/min: no adjustment. GFR < 30 m L/min: avoid use due to risk of CNS depression and accumulation of metabolites.
Cr Cl 30-50 m L/min: administer every 24 hours. Cr Cl <30 m L/min: not recommended. Hemodialysis: not recommended. Peritoneal dialysis: not recommended.
Child-Pugh A (mild): no adjustment. Child-Pugh B (moderate): reduce dose by 50% or prolong dosing interval. Child-Pugh C (severe): avoid use.
Child-Pugh A: no adjustment. Child-Pugh B: reduce dose by 50% or extend interval to every 24 hours. Child-Pugh C: not recommended.
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.
Children ≥12 years: same as adult. Children 6-11 years: guaifenesin 300 mg / dextromethorphan 15 mg orally every 12 hours, not to exceed 2 doses in 24 hours. Children <6 years: not recommended.
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.
Start at lower end of dosing range (e.g., one tablet every 24 hours) due to age-related renal and hepatic decline; monitor for CNS effects and constipation.
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.
None
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
Do not use for persistent/chronic cough, cough with excessive phlegm, or cough due to smoking/asthma/COPD/emphysema,Serotonin syndrome risk with MAOIs or other serotonergic drugs,Dextromethorphan abuse potential,Hypersensitivity reactions
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)
Concomitant use with MAOIs or within 14 days of MAOI therapy,Hypersensitivity to any component
Avoid grapefruit juice as it may increase dextromethorphan levels. No significant food interactions with promethazine.
No significant food-drug interactions. However, alcohol may potentiate CNS effects (drowsiness/dizziness) and should be avoided.
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).
FDA Category C for guaifenesin and dextromethorphan. First trimester: limited human data; animal studies show no evidence of teratogenicity at clinically relevant doses. Second and third trimesters: no known fetal risks at recommended doses. Avoid high doses of dextromethorphan due to potential serotonin reuptake inhibition and theoretical risk of fetal serotonin syndrome.
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.
Guaifenesin: excreted into breast milk in small amounts; no known adverse effects in infants at maternal therapeutic doses. Dextromethorphan: likely excreted into breast milk in low concentrations; M/P ratio not established. Use caution; monitor infant for sedation, respiratory depression, or constipation.
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.
No dose adjustment required for guaifenesin or dextromethorphan during pregnancy. Pharmacokinetic changes in pregnancy (e.g., increased renal clearance) are not clinically significant at standard doses. Use the lowest effective dose for the shortest duration.
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.
Mucinex DM combines guaifenesin (expectorant) and dextromethorphan (antitussive). Guaifenesin is best taken with adequate fluid intake to thin mucus. Dextromethorphan is contraindicated with MAOIs and in patients with serotonin syndrome risk. Avoid use in patients with chronic cough due to smoking, asthma, or COPD without physician guidance.
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.
Take with a full glass of water to help loosen phlegm.,Do not crush or chew extended-release tablets; swallow whole.,Avoid driving or operating machinery if drowsy or dizzy.,Do not use with other cough/cold medications containing dextromethorphan.,Stop use and consult doctor if cough persists >7 days or with fever, rash, or headache.
"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."
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about PROMETH W/ DEXTROMETHORPHAN vs MUCINEX DM, answered by our medical review team.
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.. MUCINEX DM is a Expectorant/Antitussive Combination that works by Guaifenesin increases respiratory tract fluid secretion to reduce mucus viscosity; dextromethorphan acts on sigma-1 receptors and NMDA receptor antagonism to suppress cough reflex.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between PROMETH W/ DEXTROMETHORPHAN and MUCINEX DM 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 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.. The standard adult dose of MUCINEX DM is: One tablet (guaifenesin 600 mg / dextromethorphan HBr 30 mg) orally every 12 hours, not to exceed 2 tablets 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 PROMETH W/ DEXTROMETHORPHAN and MUCINEX DM 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. 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. MUCINEX DM is classified as Category C. FDA Category C for guaifenesin and dextromethorphan. First trimester: limited human data; animal studies show no evidence of teratogenicity at clinically relevant doses. Second and. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.