Usage
- This combination medication is primarily prescribed for the temporary relief of symptoms associated with the common cold or allergies, including cough, nasal congestion, and runny nose. It is also used to treat symptoms of the flu such as cough, fever, headache, aches, and sore throat.
- Pharmacological Classification: Antitussive (dextromethorphan), antihistamine (diphenhydramine), and decongestant (phenylpropanolamine).
- Mechanism of Action: Dextromethorphan suppresses cough by acting on the cough center in the brain. Diphenhydramine reduces allergic symptoms by blocking histamine receptors. Phenylpropanolamine relieves nasal congestion by constricting blood vessels in the nasal passages.
Alternate Names
This specific combination does not have a widely recognized international nonproprietary name (INN). The components, however, are known by their respective INNs. It is marketed regionally under various brand names, some of which include Bromfed-DM, Dimetane DX, and Robitussin Cough and Allergy.
How It Works
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Pharmacodynamics: Dextromethorphan acts centrally on the cough center in the medulla to suppress the cough reflex. Diphenhydramine acts peripherally by blocking the H1 histamine receptors, reducing allergy symptoms like sneezing and runny nose. Phenylpropanolamine, a sympathomimetic amine, acts as an alpha-adrenergic agonist, causing vasoconstriction in the nasal mucosa, which reduces nasal congestion.
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Pharmacokinetics:
- Absorption: All three components are absorbed from the gastrointestinal tract.
- Metabolism: Dextromethorphan is primarily metabolized in the liver by the cytochrome P450 enzyme system, specifically CYP2D6. Diphenhydramine is also metabolized in the liver. Phenylpropanolamine is partially metabolized in the liver and partially excreted unchanged in the urine.
- Elimination: Dextromethorphan and its metabolites are primarily excreted in the urine. Diphenhydramine is excreted in the urine, primarily as metabolites. Phenylpropanolamine is excreted in the urine, both as unchanged drug and metabolites.
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Mode of Action: Dextromethorphan’s antitussive effect is thought to involve sigma-1 receptor agonism and antagonism of nicotinic acetylcholine receptors. Diphenhydramine competes with histamine for H1 receptor sites. Phenylpropanolamine stimulates alpha-adrenergic receptors in the nasal mucosa, leading to vasoconstriction and reduced congestion.
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Receptor Binding, Enzyme Inhibition, or Neurotransmitter Modulation: As described earlier, dextromethorphan is a sigma-1 receptor agonist and nicotinic receptor antagonist; diphenhydramine is an H1 receptor antagonist; phenylpropanolamine is an alpha-adrenergic receptor agonist.
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Elimination Pathways: Primarily renal excretion for all three drugs, after varying degrees of hepatic metabolism. Dextromethorphan is metabolized by CYP2D6 and CYP3A4.
Dosage
Standard Dosage
Children: Dosing in children is weight and age-dependent and should be carefully determined based on product-specific recommendations. Use in children under 2 years of age is generally not recommended.
Special Cases:
- Elderly Patients: Lower doses may be needed due to decreased clearance.
- Patients with Renal Impairment: Dose reduction may be necessary.
- Patients with Hepatic Dysfunction: Dose adjustment is often required.
- Patients with Comorbid Conditions: Caution is advised in patients with cardiovascular disease, diabetes, glaucoma, hyperthyroidism, prostatic hypertrophy, and other medical conditions.
Clinical Use Cases
This combination medication is not typically used in clinical settings like intubation, surgical procedures, mechanical ventilation, or the ICU due to the potential for adverse effects like sedation, respiratory depression, and cardiovascular effects.
Dosage Adjustments
Adjustments are necessary for patients with renal or hepatic impairment.
Side Effects
Common Side Effects
Drowsiness, dizziness, dry mouth, constipation, blurred vision, and urinary retention.
Rare but Serious Side Effects
Allergic reactions (e.g., rash, itching, swelling), difficulty breathing, irregular heartbeat, hallucinations, and seizures.
Long-Term Effects
Chronic use may increase the risk of cognitive impairment, especially in older adults. Overuse can lead to dependence.
Adverse Drug Reactions (ADR)
Severe allergic reactions, cardiac arrhythmias, and serotonin syndrome (when combined with other serotonergic drugs).
Contraindications
Hypersensitivity to any of the components, MAOI use within 14 days, severe cardiovascular disease, narrow-angle glaucoma, urinary retention, and severe hepatic or renal dysfunction.
Drug Interactions
MAOIs, alcohol, other CNS depressants, anticholinergic drugs, and certain antidepressants.
Pregnancy and Breastfeeding
Use with caution during pregnancy and breastfeeding due to potential risks to the fetus or infant.
Drug Profile Summary
- Mechanism of Action: Centrally acting antitussive, H1-receptor antagonist, alpha-adrenergic agonist.
- Side Effects: Drowsiness, dizziness, dry mouth, constipation, blurred vision.
- Contraindications: Hypersensitivity, MAOI use, severe cardiovascular disease.
- Drug Interactions: MAOIs, alcohol, CNS depressants.
- Pregnancy & Breastfeeding: Use with caution.
- Dosage: Adult and pediatric dosages vary based on the specific product.
- Monitoring Parameters: Respiratory rate, blood pressure, heart rate.
Popular Combinations
This particular combination is itself a popular combination for cold and allergy symptoms. It is sometimes combined with analgesics/antipyretics like acetaminophen for additional symptom relief.
Precautions
- Patients should be screened for relevant medical conditions before use.
- Caution in patients with underlying cardiovascular disease, hepatic/renal impairment, or glaucoma.
- Avoid concurrent use with alcohol or other CNS depressants.
- Driving or operating machinery may be impaired due to drowsiness.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Dextromethorphan Hydrobromide + Diphenhydramine + Phenylpropanolamine?
A: It varies based on the formulation. Consult the product’s labeling for specific instructions. Typically for adults, the doses range from 10-30mg for dextromethorphan, 12.5-50mg for diphenhydramine, and 5-15mg for phenylpropanolamine every 4-6 hours. Doses are typically lower for children and adjusted downwards further in cases of liver and kidney problems.
Q2: What are the key contraindications?
A: Concurrent or recent MAOI use, severe liver or kidney disease, certain heart problems, glaucoma, and difficulty urinating.
Q3: What are the common side effects?
A: Drowsiness, dry mouth, blurred vision, constipation, and dizziness.
Q4: Can this medication be used during pregnancy?
A: Consult a physician. There may be risks associated. If so, caution and appropriate monitoring are essential.
Q5: Can I operate machinery while taking this medication?
A: No, it may cause drowsiness and impair alertness and reaction time.
Q6: Is this drug addictive?
A: While the components alone do not pose an addictive risk at the recommended doses, DXM abuse can be encountered and is often accompanied by concomitant abuse of other agents, leading to physiological and psychological issues including dependence, overdose, acute psychosis and fatal serotonin syndrome.
Q7: What if I miss a dose?
A: Take the missed dose as soon as you remember, unless it’s close to the next scheduled dose. Do not double the dose.
Q8: Can this be taken with alcohol?
A: No, avoid alcohol while taking this medicine as it can potentiate drowsiness and other CNS depressant effects.
Q9: What is this combination medicine typically used to treat?
A: It is usually used for relieving symptoms related to the common cold or allergies including cough, nasal congestion, and runny nose.
Q10: How long should I take this medication?
A: It should only be used for short-term symptom relief. If symptoms persist for more than 7 days or worsen, consult a physician.
