Usage
Dextromethorphan Hydrobromide + Diphenhydramine is primarily prescribed for the temporary relief of cough and cold symptoms, including:
- Dry, non-productive cough
- Runny nose
- Sneezing
- Itching
- Watery eyes
It’s also used to aid restful sleep when cough interferes with it.
Pharmacological Classification:
- Antitussive (Dextromethorphan)
- Antihistamine (Diphenhydramine)
Mechanism of Action:
Dextromethorphan suppresses cough by acting on the cough center in the medulla oblongata within the brainstem, thereby increasing the threshold for the cough reflex. Diphenhydramine, as an antihistamine, works by blocking the effects of histamine, a chemical mediator responsible for allergic symptoms like runny nose, sneezing, and itching. Additionally, diphenhydramine has sedative properties.
Alternate Names
While “Dextromethorphan Hydrobromide + Diphenhydramine” is the generic name, there may be regional or international variations. Brand names vary depending on the region and manufacturer. Some examples include Hydryllin DM syrup, Robitussin DM and others.
How It Works
Pharmacodynamics: Dextromethorphan acts centrally on the cough center in the brain. Diphenhydramine acts peripherally by blocking histamine H1 receptors.
Pharmacokinetics:
- Absorption: Both drugs are well-absorbed from the gastrointestinal tract.
- Metabolism: Dextromethorphan is extensively metabolized in the liver, primarily by the cytochrome P450 enzyme system. Diphenhydramine is also metabolized in the liver.
- Elimination: Both drugs and their metabolites are primarily excreted in the urine.
Mode of Action: Dextromethorphan acts primarily within the central nervous system by suppressing the cough reflex. It binds to sigma-1 receptors and, to a lesser extent, NMDA receptors in the brain. The exact mechanism isn’t fully understood, but it increases the cough threshold and doesn’t have opioid-like effects despite its structural similarity to codeine. Diphenhydramine competitively antagonizes the effects of histamine at H1 receptors. This leads to a reduction in allergic symptoms such as sneezing, rhinorrhea, and itching.
Receptor Binding/Enzyme Inhibition/Neurotransmitter Modulation: Dextromethorphan primarily acts on sigma-1 receptors and, to a lesser extent, on NMDA receptors in the brain. Diphenhydramine binds to and blocks H1 histamine receptors.
Elimination Pathways: Both drugs and their metabolites are primarily eliminated through renal excretion.
Dosage
Standard Dosage
Adults: A typical dose is 10-20 mg of dextromethorphan and 12.5-25 mg of diphenhydramine every 4-6 hours as needed. The maximum daily dose for dextromethorphan should not exceed 120 mg. For diphenhydramine, the maximum daily dose should not exceed 300 mg.
Children: Dosage should be based on the child’s weight and age. Consult a healthcare professional for specific pediatric dosing recommendations. Do not use this medicine only to make a child sleepy.
Special Cases: Dosage adjustments may be necessary based on organ function and other medical conditions. Consult medical resources for specific guidelines for these situations.
Clinical Use Cases
The combination of Dextromethorphan Hydrobromide + Diphenhydramine is typically not used in clinical settings like intubation, surgical procedures, mechanical ventilation, ICU, or emergency situations.
Dosage Adjustments
Adjustments are necessary for patients with renal or hepatic impairment. Consult medical guidelines for specific recommendations based on creatinine clearance or liver function tests.
Side Effects
Common Side Effects
- Drowsiness
- Dizziness
- Dry mouth
- Blurred vision
- Constipation
- Nausea
- Upset stomach
- Restlessness or excitability (especially in children)
Rare but Serious Side Effects
- Allergic reactions (e.g., hives, difficulty breathing, swelling)
- Seizures
- Severe drowsiness
- Fast or irregular heartbeat
- Difficulty urinating
- Confusion, anxiety, irritability, tremors
Long-Term Effects
Chronic complications from prolonged use are uncommon, but it is important to avoid overuse and consult a physician if symptoms persist.
Adverse Drug Reactions (ADR)
Clinically significant ADRs that necessitate immediate intervention include severe allergic reactions, seizures, cardiac arrhythmias, and signs of serotonin syndrome (if taken with serotonergic drugs).
Contraindications
- Hypersensitivity to either drug
- MAO inhibitor use within the past 14 days
- Asthma, COPD, or other respiratory conditions
- Blockage in the digestive tract
- Glaucoma
Drug Interactions
- MAO inhibitors (can cause a dangerous drug interaction)
- CNS depressants (e.g., alcohol, opioids, sedatives) – may increase drowsiness
- Anticholinergic drugs – may increase anticholinergic effects
- Serotonergic drugs – may increase risk of serotonin syndrome
Pregnancy and Breastfeeding
- Pregnancy: Consult medical advice before use. There is limited data about its effect on an unborn baby. Dextromethorphan is generally considered safe, while diphenhydramine’s safety profile is less clear.
- Breastfeeding: Use with caution. Both drugs can pass into breast milk, although in small amounts. Monitor the infant for drowsiness or poor feeding.
Drug Profile Summary
- Mechanism of Action: See “How It Works” section
- Side Effects: See “Side Effects” section
- Contraindications: See “Contraindications” section
- Drug Interactions: See “Drug Interactions” section
- Pregnancy & Breastfeeding: See “Pregnancy and Breastfeeding” section
- Dosage: See “Dosage” section
- Monitoring Parameters: Monitor for side effects, especially drowsiness and respiratory depression. Evaluate cough and cold symptoms.
Popular Combinations
Dextromethorphan and diphenhydramine are often combined with other medications, such as guaifenesin (an expectorant) and phenylephrine (a decongestant), to address multiple cold and flu symptoms.
Precautions
- General Precautions: Screen patients for allergies, other medical conditions, current medications.
- Specific Populations: Consult guidelines for dosage adjustments during pregnancy, breastfeeding, and in pediatric and elderly patients.
- Lifestyle Considerations: Caution patients about driving or operating machinery while taking the medication due to potential drowsiness. Advise against alcohol consumption.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Dextromethorphan Hydrobromide + Diphenhydramine?
A: The typical adult dose is 10-20 mg of dextromethorphan and 12.5-25 mg of diphenhydramine every 4-6 hours as needed. Pediatric dosing should be determined by a healthcare professional based on the child’s weight and age.
Q2: What are the common side effects?
A: Common side effects include drowsiness, dizziness, dry mouth, blurred vision, constipation, and nausea.
Q3: Can pregnant or breastfeeding women take this medication?
A: Consult a healthcare professional before use during pregnancy or breastfeeding.
Q4: What are the serious side effects to watch out for?
A: Serious side effects include allergic reactions, seizures, severe drowsiness, fast or irregular heartbeat, and difficulty urinating.
Q5: What are the contraindications to this medication?
A: Contraindications include hypersensitivity to the drugs, MAO inhibitor use, severe respiratory conditions, glaucoma, and blockage in the digestive tract.
Q6: What other medications interact with this combination?
A: It interacts with MAO inhibitors, CNS depressants, and some other medications.
Q7: Can this medicine be used to treat a cough caused by smoking or asthma?
A: No, this medicine is not effective for coughs caused by smoking, asthma, or emphysema.
Q8: What should patients avoid while taking this medication?
A: Patients should avoid alcohol, driving, and operating machinery. They should also avoid taking other medications that contain dextromethorphan or diphenhydramine without consulting a doctor.
Q9: What should a patient do if they experience side effects?
A: Contact a healthcare professional if side effects are bothersome or severe. For serious side effects, seek immediate medical attention.
Q10: Is it safe to take this medication with other cold and flu medications?
A: It is best to avoid taking this combination with other cold and flu medications without first consulting a doctor or pharmacist. Some other cold and flu medications might contain the same ingredients and could lead to an overdose if taken together.
