Dextromethorphan Hydrobromide is a synthetic, centrally-acting, non-opioid antitussive agent. It is the d-isomer of the codeine analogue, levorphanol, but lacks significant analgesic, sedative, or respiratory depressant properties at therapeutic doses. It is a Schedule H drug in India, widely used for the symptomatic relief of non-productive (dry) cough associated with upper respiratory tract infections, allergies, and common cold. It acts by elevating the cough threshold in the medullary cough center.
Adult: 10-20 mg every 4 hours, or 30 mg every 6-8 hours. Maximum: 120 mg per day.
Note: For oral use only. Can be taken with or without food. Shake the syrup well before use. Use the measuring cup or spoon provided for accurate dosing. Do not crush or chew sustained-release formulations.
Dextromethorphan and its primary metabolite, dextrorphan, act as non-competitive antagonists at the N-methyl-D-aspartate (NMDA) receptor. This action is responsible for its cough suppressant effect by depressing the cough center in the medulla oblongata. It also acts as an agonist at sigma-1 receptors and inhibits the reuptake of serotonin and norepinephrine, though these effects are more relevant at higher, non-therapeutic doses.
Pregnancy: Category C (US FDA). Animal studies have shown adverse effects. There are no adequate and well-controlled studies in pregnant women. Use only if the potential benefit justifies the potential risk to the fetus. Avoid in the first trimester unless clearly needed.
Driving: May cause dizziness and drowsiness. Patients should be cautioned against driving or operating heavy machinery until their response to the drug is known.
| Monoamine Oxidase Inhibitors (MAOIs) e.g., Phenelzine, Selegiline, Moclobemide | Risk of life-threatening serotonin syndrome, hyperpyrexia, and death. | 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 plasma levels of dextromethorphan, leading to enhanced effects and toxicity. | Moderate |
| CYP3A4 Inhibitors (e.g., Ketoconazole, Clarithromycin, Ritonavir) | Increased plasma levels of dextromethorphan. | Moderate |
| CYP3A4 Inducers (e.g., Rifampicin, Carbamazepine, Phenytoin) | Decreased plasma levels and efficacy of dextromethorphan. | Moderate |
| Alcohol, Benzodiazepines, Opioids, Sedative-hypnotics | Additive CNS depression, impaired alertness, and increased risk of respiratory depression. | Major |
| Antihistamines (e.g., Chlorpheniramine, Diphenhydramine) | Additive sedative effects. | Moderate |
Same composition (Dextromethorphan Hydrobromide (NA)), different brands: