Dextromethorphan + Phenylephrine
Dose Calculator
India · Paediatric (4 yr+) & Adult · Dry Cough + Nasal Congestion · Kofarest · Ascoril DX · Grilinctus · Alex
Cough Syrup Dose Calculator
| Component | Per dose | Max/day | Safe limit |
|---|
Kofarest-D — DXM 10mg + PE 5mg/5ml
Alex — DXM 10mg + PE 5mg/5ml
Grilinctus DX — DXM 10mg + PE 5mg/5ml
Ascoril DX — DXM 10mg + PE 5mg/5ml
Wikoryl — DXM 5mg + PE 5mg/5ml (paeds)
Coscopin-D — DXM 10mg + PE 5mg/5ml
⚠️ Always check the label — strengths vary between brands
🚫 Critical safety warnings — read before prescribing
- Under 4 years: Absolutely contraindicated. CDSCO, FDA, MHRA, and WHO all advise against DXM-containing cough syrups in children under 4 (and ideally under 6) years. There is no proven benefit, and the risks include respiratory depression, sedation, seizures, and death from accidental overdose.
- DXM abuse potential: At high doses (10× therapeutic), dextromethorphan causes dissociative effects ("robo-tripping"). Ensure the dose prescribed is age and weight appropriate. Do not dispense large quantities to adolescents without clinical justification.
- MAO inhibitor interaction — life-threatening: DXM is absolutely contraindicated with MAO inhibitors (phenelzine, tranylcypromine, selegiline, linezolid). The combination causes serotonin syndrome — hyperthermia, agitation, rigidity, autonomic instability. Allow ≥14 days washout after MAOI before giving DXM.
- Phenylephrine in hypertension: Even oral phenylephrine can raise blood pressure. Avoid in uncontrolled hypertension, within 14 days of MAOI, in hyperthyroidism, and with certain antidepressants (TCAs, SNRIs).
- Wet / productive cough: Do not suppress a productive cough in children — the cough reflex helps clear secretions and prevents pneumonia. Antitussives should only be used for dry, non-productive cough.
- Do not use for longer than 7 days without medical review. Persistent cough may indicate asthma, TB, whooping cough, or another underlying cause requiring investigation.
- Always use a measuring syringe — never a household teaspoon. A standard teaspoon holds 3–5 ml; inaccurate measuring is a leading cause of overdose in children.
Dextromethorphan + Phenylephrine — Dosing Reference Table
| Age group | DXM dose | Volume (10mg/5ml syrup) | Frequency | Max/day |
|---|---|---|---|---|
| Under 4 years | NOT RECOMMENDED | Do not use | Contraindicated | — |
| 4–6 years (15–20 kg) | 2.5–5 mg per dose | 1.25–2.5 ml | Every 6–8 hours PRN | 15 mg/day (doctor supervised) |
| 6–12 years (20–40 kg) | 5–10 mg per dose | 2.5–5 ml | Every 6–8 hours PRN | 30–40 mg/day |
| 12–18 years (≥40 kg) | 10–15 mg per dose | 5–7.5 ml | Every 6–8 hours | 60 mg/day |
| Adult | 10–20 mg per dose | 5–10 ml (or 1 × 30mg tab) | Every 4–8 hours | 120 mg/day |
| Adult — phenylephrine | PE 5–10 mg per dose | As per combination product | Every 4–6 hours | PE max 60 mg/day |
Dextromethorphan + Phenylephrine — Clinical Guide India
Dextromethorphan (DXM) and phenylephrine (PE) combination cough syrups are among the most commonly purchased OTC medications in India under brand names including Kofarest-D, Alex, Grilinctus DX, Ascoril DX, and Coscopin-D. DXM is an antitussive (cough suppressant) that works by suppressing the cough reflex centre in the medulla via NMDA receptor antagonism. Phenylephrine is a decongestant that reduces nasal mucosal oedema through α1-adrenergic vasoconstriction. The combination is intended for dry, irritating cough accompanied by nasal congestion — typically in URTI, post-nasal drip, and allergic rhinitis.
Age restrictions — why under-4 is an absolute limit
The Central Drugs Standard Control Organisation (CDSCO), the US FDA, UK MHRA, and WHO all advise that DXM-containing cough syrups should not be used in children under 4 years of age. In 2022, CDSCO updated labelling requirements to prominently state this on all DXM products. The key reasons: children under 4 have a steep dose-response curve for DXM's CNS effects; the ratio between therapeutic and toxic doses is narrow; and accidental overdose (by giving multiple doses or using concentrated adult formulations) is easy and has caused deaths. Additionally, the cough reflex in young children is physiologically protective — suppressing it in bronchiolitis, pneumonia, or other lower respiratory infections can delay secretion clearance and worsen outcomes.
For children aged 4–6 years, cough syrups should only be used under a doctor's prescription, with weight-based dosing strictly followed. Even in this age group, first-line management of cough should be saline nasal drops for congestion, adequate hydration, and honey (for children over 1 year) — which has evidence comparable to DXM for symptomatic cough relief.
DXM serotonin syndrome and MAOI interaction
Dextromethorphan inhibits serotonin reuptake at higher doses and can precipitate serotonin syndrome when combined with MAO inhibitors (phenelzine, tranylcypromine, selegiline, and the antibiotic linezolid which has weak MAOI activity). Serotonin syndrome causes hyperthermia, agitation, myoclonus, hyperreflexia, diaphoresis, and tachycardia — it can be life-threatening. A 14-day washout period after stopping any MAOI is mandatory before DXM can be safely given. Always screen for MAOI use before prescribing or recommending any DXM-containing product.
Phenylephrine — the oral decongestant controversy
The clinical evidence for oral phenylephrine as a nasal decongestant has been controversial. A 2023 FDA advisory committee concluded that oral phenylephrine at the standard OTC dose (10 mg per dose) is no more effective than placebo for nasal congestion when taken orally — due to extensive first-pass hepatic metabolism reducing bioavailability to approximately 38%. Despite this, oral PE is still widely used in India and remains included in most combination cough syrups. At clinical doses in combination products, the nasal decongestion benefit may be modest, but cardiovascular side effects (blood pressure elevation, tachycardia) are still possible, particularly in patients with hypertension or thyroid disease.