1. Clinical Overview
Dextromethorphan Hydrobromide is a centrally-acting, non-opioid antitussive agent. It is the d-isomer of the codeine analog, levorphanol, but lacks significant analgesic, sedative, or addictive properties at therapeutic doses. It is a standard component in numerous over-the-counter (OTC) and prescription cough and cold formulations in India, widely used for the symptomatic relief of non-productive (dry) cough.
| 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 suppresses cough by elevating the threshold for coughing in the cough center located in the medulla oblongata. It does not inhibit ciliary activity. Its action is not mediated through opioid receptors, hence it lacks respiratory depression and significant constipation at standard antitussive doses.
3. Indications & Uses
- Symptomatic relief of non-productive (dry) cough associated with upper respiratory tract infections (common cold, influenza)
- Symptomatic relief of cough due to minor throat and bronchial irritation.
4. Dosage & Administration
Adult Dosage: 5mg to 20mg every 4 to 8 hours. Maximum: 120mg per 24 hours. Typical OTC dose: 5-10mg.
Administration: Oral administration. Can be taken with or without food. Tablet/Syrup: Swallow whole with water. Do not crush or chew sustained-release formulations. Use a calibrated measuring device for liquid formulations. Do not use for more than 7 days for self-medication. If cough persists, consult a physician.
5. Side Effects
Common side effects may include:
- Drowsiness
- Dizziness
- Nausea
- Gastrointestinal upset
- Fatigue
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Monoamine Oxidase Inhibitors (MAOIs) e.g., Phenelzine, Selegiline, Moclobemide | Risk of severe, potentially fatal serotonin syndrome. | Contraindicated |
| Selective Serotonin Reuptake Inhibitors (SSRIs) e.g., Fluoxetine, Sertraline | Increased risk of serotonin syndrome. | Major |
| Serotonin-Norepinephrine Reuptake Inhibitors (SNRIs) e.g., Venlafaxine, Duloxetine | Increased risk of serotonin syndrome. | Major |
| Other serotonergic drugs (Tramadol, Tapentadol, Triptans, Linezolid) | Increased risk of serotonin syndrome. | Major |
| CYP2D6 Inhibitors (e.g., Quinidine, Paroxetine, Fluoxetine) | Increased dextromethorphan levels, converting extensive metabolizers to poor metabolizer phenotype, increasing toxicity risk. | Moderate |
| CYP3A4 Inhibitors (e.g., Ketoconazole, Clarithromycin, Grapefruit juice) | Increased dextromethorphan levels. | Moderate |
| Alcohol, Benzodiazepines, Opioids, Sedative Antihistamines | Additive CNS depression (drowsiness, dizziness, impaired coordination). | Moderate |
| Anticholinergic drugs | Additive anticholinergic effects (dry mouth, blurred vision, urinary retention). | Moderate |
7. Patient Counselling
- DO take exactly as directed. Do not exceed the recommended dose or frequency.
- DO use a proper measuring spoon/cup for liquid doses.
- DO consult a doctor if cough persists for more than 7 days, is accompanied by high fever, rash, or persistent headache.
- DO NOT take with alcohol or other sedative medicines.
- DO NOT give to children under 4 years of age without doctor's advice.
- DO NOT use for chronic cough due to smoking, asthma, or emphysema unless directed by a doctor.
- DO NOT crush or chew sustained-release tablets.
8. Toxicology & Storage
Overdose: Nausea, vomiting, drowsiness, dizziness, blurred vision, nystagmus, ataxia, slurred speech, tachycardia, hypertension, respiratory depression (at very high doses), stupor, coma, seizures, serotonin syndrome (if combined with other serotonergics), and death in extreme cases.
Storage: Store at room temperature (15-30°C), protected from light and moisture. Keep in original container, tightly closed. Keep out of reach and sight of children. Do not use after the expiry date printed on the pack. Do not freeze syrups.