Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
PROMETH W/ DEXTROMETHORPHAN vs AMMONIUM CHLORIDE 2.14%
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.
Ammonium chloride is an acidifying agent. It dissociates into ammonium and chloride ions. The ammonium ion is metabolized in the liver to urea and hydrogen ions, leading to metabolic acidosis. This reduces blood p H and increases renal excretion of alkaline urine.
Symptomatic relief of cough associated with upper respiratory tract infections,Allergic rhinitis,Motion sickness,Nausea and vomiting,Sedation
Treatment of metabolic alkalosis,Urinary acidification to enhance excretion of weak bases (e.g., amphetamines, quinidine) or to promote dissolution of calcium phosphate stones
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.
For metabolic alkalosis: 1.5 to 3 g (approximately 280 to 560 m Eq) intravenously over 4 to 6 hours; adjust based on serum chloride and p H.
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.
4-6 hours; prolonged in renal impairment (up to 12-15 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.
Converted to urea and hydrogen ions in the liver via the urea cycle.
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%).
Renal: >99% as ammonium ion and chloride; minimal biliary/fecal elimination.
Promethazine: 93% bound primarily to albumin. Dextromethorphan: 60-70% bound to albumin and alpha-1-acid glycoprotein.
Negligible (<1%); not significantly bound to plasma proteins.
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.
0.3-0.5 L/kg; distributes primarily in extracellular fluid; clinical meaning: low Vd reflects limited tissue penetration.
Promethazine: oral 25% (extensive first-pass metabolism), intramuscular 100%, rectal 70-80%. Dextromethorphan: oral 11-60% (dependent on CYP2D6 metabolism), intramuscular not available.
Oral: 100% (fully absorbed); IV: 100%; topical: non-systemic.
GFR ≥ 30 m L/min: no adjustment. GFR < 30 m L/min: avoid use due to risk of CNS depression and accumulation of metabolites.
Contraindicated in severe renal impairment (GFR <30 m L/min). For GFR 30-60 m L/min: reduce dose by 50% and monitor serum electrolytes. For GFR >60 m L/min: no adjustment.
Child-Pugh A (mild): no adjustment. Child-Pugh B (moderate): reduce dose by 50% or prolong dosing interval. Child-Pugh C (severe): avoid use.
No specific Child-Pugh based adjustment; use caution in severe hepatic impairment due to risk of ammonia toxicity.
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.
Neonates and children: 1-2 m Eq/kg intravenously per dose, infused over 2-4 hours; maximum 100 m Eq per dose. Titrate based on serum chloride and acid-base status.
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 adult dosing (e.g., 1.5 g intravenously) due to age-related decreased renal function; monitor electrolytes and renal function closely.
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
Avoid in patients with impaired renal or hepatic function; may cause hyperammonemia and hepatic coma.,Use with caution in patients with cardiac failure or pulmonary edema due to risk of fluid overload.,Monitor serum chloride, bicarbonate, and p H levels during therapy.
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)
Severe hepatic insufficiency,Severe renal impairment,Hyperammonemia,Uremia,Ammonium toxicity
Avoid grapefruit juice as it may increase dextromethorphan levels. No significant food interactions with promethazine.
No significant food interactions known. However, a diet low in chloride may reduce efficacy. Avoid excessive intake of alkalinizing foods (e.g., citrus fruits, vegetables) that may counteract the acidifying effect.
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).
Ammonium chloride is not known to be teratogenic in humans. No structural anomalies have been reported with first trimester exposure. In second and third trimesters, maternal acidosis from excessive dosing could potentially affect fetal acid-base balance, but no specific fetal risks are documented. Overall, classified as FDA Pregnancy Category C.
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.
Excretion into breast milk is unknown. M/P ratio not available. Caution advised due to potential for neonatal acidosis if maternal doses are high. Short-term use is likely compatible with breastfeeding.
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 specific dosing adjustments required in pregnancy. However, due to pregnancy-associated hyperventilation and renal changes, monitor acid-base status. Initiate at low doses and titrate based on serum chloride and bicarbonate levels.
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.
Ammonium chloride 2.14% is a systemic acidifying agent used to treat metabolic alkalosis. Monitor serum electrolytes (especially chloride and bicarbonate) and arterial blood gases closely. Avoid in patients with severe hepatic or renal impairment, as ammonium ions can precipitate hepatic encephalopathy or worsen acidosis. Infuse slowly to prevent hemolysis. Use with caution in patients with respiratory acidosis.
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.
This medication is used to treat low acid levels in the blood.,Your healthcare provider will monitor your blood tests regularly while on this medicine.,Report any signs of allergic reaction (rash, itching, swelling) or symptoms of acidosis (confusion, rapid breathing) immediately.,Avoid taking other medications or supplements without consulting your doctor, as they may interfere with this treatment.,Do not stop this medication abruptly without medical advice.
"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."
"Ammonium chloride, an acidifying agent, reduces urinary pH, which increases the renal clearance of lisdexamfetamine and its active metabolite d-amphetamine. This accelerated elimination leads to decreased systemic exposure and potentially diminished therapeutic efficacy of lisdexamfetamine. Clinically, patients may experience reduced symptom control for ADHD or binge eating disorder, requiring dose adjustments or alternative therapies."
"Sufentanil, a potent opioid analgesic, may increase renal excretion of ammonium chloride by promoting diuresis through opioid-induced release of antidiuretic hormone (ADH) and subsequent water reabsorption, leading to dilutional acidosis and enhanced ammonium excretion. This interaction can result in reduced serum ammonium levels and decreased efficacy of ammonium chloride as an acidifying agent, potentially compromising its therapeutic effect in metabolic alkalosis or urinary tract infections. Clinical outcomes may include incomplete correction of metabolic alkalosis or reduced antimicrobial activity of ammonium chloride in the urine."
"Ammonium chloride acidifies the urine, which increases the renal excretion of amphetamine by favoring its ionized form in the tubular lumen, thereby reducing its reabsorption. This leads to a decreased serum concentration of amphetamine and potentially diminished therapeutic efficacy. Clinically, patients may experience reduced mood-elevating or stimulant effects, requiring dose adjustment."
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about PROMETH W/ DEXTROMETHORPHAN vs AMMONIUM CHLORIDE 2.14%, 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.. AMMONIUM CHLORIDE 2.14% is a Expectorant/Systemic Acidifier that works by Ammonium chloride is an acidifying agent. It dissociates into ammonium and chloride ions. The ammonium ion is metabolized in the liver to urea and hydrogen ions, leading to metabolic acidosis. This reduces blood p H and increases renal excretion of alkaline urine.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between PROMETH W/ DEXTROMETHORPHAN and AMMONIUM CHLORIDE 2.14% 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 AMMONIUM CHLORIDE 2.14% is: For metabolic alkalosis: 1.5 to 3 g (approximately 280 to 560 m Eq) intravenously over 4 to 6 hours; adjust based on serum chloride and p H.. 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 AMMONIUM CHLORIDE 2.14% 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. AMMONIUM CHLORIDE 2.14% is classified as Category C. Ammonium chloride is not known to be teratogenic in humans. No structural anomalies have been reported with first trimester exposure. In second and third trimesters, maternal acido. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.