Usage
- This combination medication is primarily prescribed for the temporary relief of cough and upper respiratory symptoms (such as runny nose, sneezing, itchy or watery eyes) associated with the common cold or allergies.
- Pharmacological Classification: Antitussive (dextromethorphan) and antihistamine (promethazine).
- Mechanism of Action: Dextromethorphan suppresses the cough reflex by acting on the cough center in the medulla oblongata. Promethazine blocks the effects of histamine, reducing allergy symptoms.
Alternate Names
- Promethazine DM
- Promethazine with Dextromethorphan
- Promethazine with DM
How It Works
- Pharmacodynamics: Dextromethorphan acts centrally on the cough center in the brain. Promethazine exerts its antihistaminic effects by blocking H1 receptors, thereby reducing symptoms like itching, sneezing, and runny nose. It also has anticholinergic and sedative properties.
- Pharmacokinetics:
- Absorption: Both drugs are absorbed orally.
- Metabolism: Both are primarily metabolized in the liver by the CYP2D6 enzyme.
- Elimination: Primarily eliminated via renal excretion.
- Mode of Action: Dextromethorphan acts on sigma opioid receptors in the central nervous system, suppressing the cough reflex. It does not have analgesic or addictive properties like other opioids. Promethazine competes with histamine for H1 receptor sites on effector cells in the respiratory tract, blood vessels, and gastrointestinal smooth muscle.
- Receptor Binding/Enzyme Inhibition/Neurotransmitter Modulation: Dextromethorphan: Sigma opioid receptor agonist. Promethazine: H1 receptor antagonist.
Dosage
Standard Dosage
Adults and children 12 years and older:
- 5 mL (1 teaspoon) orally every 4 to 6 hours.
- Maximum: 30 mL in 24 hours.
Children:
- 6 to 11 years: 2.5 mL to 5 mL (1/2 to 1 teaspoon) orally every 4 to 6 hours. Maximum: 20 mL in 24 hours.
- 2 to 5 years: 1.25 mL to 2.5 mL (1/4 to 1/2 teaspoon) orally every 4 to 6 hours. Maximum: 10 mL in 24 hours.
Note: This medication is contraindicated in children under 2 years of age due to the risk of fatal respiratory depression.
Special Cases:
- Elderly Patients: Lower doses may be necessary.
- Patients with Renal Impairment: Dose adjustment may be required.
- Patients with Hepatic Dysfunction: Dose adjustment may be required.
- Patients with Comorbid Conditions: Use with caution in patients with cardiovascular disease, respiratory conditions like asthma or COPD, glaucoma, prostatic hypertrophy, or bladder neck obstruction.
Clinical Use Cases
This combination is generally not indicated for the listed clinical scenarios. Its use is primarily limited to symptomatic relief of cough and cold symptoms.
Dosage Adjustments
Dose modifications may be necessary based on renal or hepatic function, age, and other patient-specific factors.
Side Effects
Common Side Effects
- Drowsiness
- Dizziness
- Blurred vision
- Dry mouth
- Nausea
- Vomiting
Rare but Serious Side Effects
- Respiratory depression
- Extrapyramidal symptoms (e.g., dystonia, akathisia, tardive dyskinesia)
- Neuroleptic malignant syndrome
- Seizures
- Allergic reactions (e.g., rash, hives, angioedema)
Long-Term Effects
Chronic use of promethazine can lead to tardive dyskinesia.
Adverse Drug Reactions (ADR)
Severe allergic reactions, respiratory depression, neuroleptic malignant syndrome.
Contraindications
- Children under 2 years of age
- Hypersensitivity to promethazine or other phenothiazines
- Coma
- Monoamine oxidase inhibitor (MAOI) use within the past 14 days
- Asthma or lower respiratory tract symptoms
Drug Interactions
- MAOIs
- Alcohol
- CNS depressants (e.g., sedatives, hypnotics, opioids, some antidepressants)
- Anticholinergic drugs
- Antihypertensive medications
Pregnancy and Breastfeeding
- Pregnancy: Use only if clearly needed and the potential benefit outweighs the potential risk to the fetus.
- Breastfeeding: Use with caution. Promethazine is excreted in breast milk. Consider the risks and benefits.
Drug Profile Summary
- Mechanism of Action: Dextromethorphan: Centrally acting cough suppressant. Promethazine: H1 receptor antagonist.
- Side Effects: Drowsiness, dizziness, blurred vision, dry mouth, nausea, vomiting.
- Contraindications: Age <2 years, hypersensitivity, coma, MAOI use.
- Drug Interactions: MAOIs, alcohol, CNS depressants.
- Pregnancy & Breastfeeding: Use with caution.
- Dosage: See dosage section.
- Monitoring Parameters: Respiratory rate, mental status.
Popular Combinations
This is often used alone and not in combination with other medications for this indication. Other medications may be indicated based on the symptoms being addressed.
Precautions
- Use cautiously in patients with cardiovascular disease, liver dysfunction, respiratory conditions, glaucoma, prostatic hypertrophy, or bladder neck obstruction.
- Avoid activities requiring alertness.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Dextromethorphan Hydrobromide + Promethazine?
A: See the detailed dosage section above.
Q2: Can this combination be used in children under 2?
A: No, it’s contraindicated due to the risk of respiratory depression.
Q3: What are the major drug interactions to be aware of?
A: MAOIs, alcohol, and CNS depressants are the most significant interactions.
Q4: What are the common side effects?
A: Drowsiness, dizziness, blurred vision, dry mouth, nausea, and vomiting.
Q5: Is it safe to use during pregnancy or breastfeeding?
A: Use with caution during pregnancy only if the benefits outweigh the risks. Limited information is available regarding breastfeeding; consult with a physician to assess risk/benefit.
Q6: Can patients operate machinery while taking this medication?
A: No, it can cause drowsiness and impair cognitive function.
Q7: How does dextromethorphan work to suppress cough?
A: It acts on the cough center in the brain.
Q8: How does promethazine alleviate allergy symptoms?
A: It blocks the action of histamine by acting as an H1 receptor antagonist.
Q9: What should be done in case of an overdose?
A: Seek immediate medical attention.
