1. Clinical Overview
Dextromethorphan Hydrobromide is a centrally-acting, non-opioid antitussive agent. It is the d-isomer of the codeine analogue, levorphanol, but lacks significant analgesic, sedative, or addictive properties at therapeutic doses. It is a standard-of-care for the symptomatic relief of non-productive cough associated with upper respiratory tract infections and allergies. In the Indian context, it is widely available as a single ingredient or in combination with antihistamines, expectorants, and decongestants.
| Onset | Duration | Bioavailability |
|---|---|---|
| 15-30 minutes | 5-6 hours for immediate-release formulations | Approximately 11% due to extensive first-pass metabolism |
2. Mechanism of Action
Dextromethorphan and its active metabolite, dextrorphan, act centrally on the cough center in the medulla oblongata to elevate the cough threshold. It suppresses the cough reflex without inhibiting ciliary activity in the respiratory tract.
3. Indications & Uses
- Symptomatic relief of non-productive (dry) cough associated with upper respiratory tract infections (common cold, influenza)
- Symptomatic relief of cough associated with allergic conditions
4. Dosage & Administration
Adult Dosage: 10-20 mg every 4-6 hours, not to exceed 120 mg in 24 hours. For 10mg strength: 1-2 tablets/capsules/spoonful every 4-6 hours.
Administration: Can be taken with or without food. Oral administration. For liquid formulations, use the measuring cup/spoon provided. Do not crush or chew sustained-release formulations. Maintain adequate hydration.
5. Side Effects
Common side effects may include:
- Drowsiness
- Dizziness
- Nausea
- Gastrointestinal upset
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Monoamine Oxidase Inhibitors (MAOIs) - e.g., Phenelzine, Selegiline, Moclobemide | Risk of severe serotonin syndrome, hyperpyrexia, hypotension, coma, and death. | Contraindicated |
| Selective Serotonin Reuptake Inhibitors (SSRIs) - e.g., Fluoxetine, Paroxetine | Increased risk of serotonin syndrome. Paroxetine is also a strong CYP2D6 inhibitor. | Major |
| Other Serotonergic Drugs (Tramadol, TCAs, Triptans, Linezolid) | Additive serotonergic effects, risk of serotonin syndrome. | Major |
| CYP2D6 Inhibitors (Quinidine, Bupropion, Terbinafine) | Markedly increased dextromethorphan plasma levels, leading to increased effects and toxicity. | Major |
| CYP3A4 Inhibitors (Ketoconazole, Clarithromycin, Ritonavir) | Increased dextromethorphan levels. | Moderate |
| CNS Depressants (Alcohol, Benzodiazepines, Opioids, Sedating Antihistamines) | Additive CNS depression, sedation, and impaired psychomotor performance. | Major |
| Anticholinergic Drugs (Atropine, TCAs, Antipsychotics) | Additive anticholinergic side effects (dry mouth, blurred vision, constipation). | Moderate |
7. Patient Counselling
- DO take exactly as prescribed/directed on the label.
- DO NOT exceed the recommended dose or frequency.
- DO NOT use for chronic cough associated with smoking, asthma, or emphysema without consulting a doctor.
- DO NOT use to suppress a productive cough (cough with phlegm).
- DO NOT crush or chew sustained-release capsules/tablets.
- DO NOT take with alcohol or other sedative medications.
- DO inform your doctor about all other medications you are taking.
8. Toxicology & Storage
Overdose: Nystagmus, diplopia, blurred vision, dizziness, ataxia, hyperexcitability, lethargy, stupor, coma, respiratory depression (especially in children), seizures, tachycardia, hypertension, nausea/vomiting, toxic psychosis with hallucinations, and serotonin syndrome in combination with other serotonergic drugs.
Storage: Store at room temperature (15-30°C), protected from light and moisture. Keep in the original container, tightly closed. Keep out of reach of children and pets. Do not use after the expiry date. For liquid formulations, do not freeze.