Robitussin
Robitussin
Generic Name
Robitussin
Mechanism
- Dextromethorphan (DM)
- Acts as a *non‑competitive NMDA receptor antagonist* in the medullary cough center, thereby reducing the cough reflex.
- Also functions as a *sigma‑1 receptor agonist* and *opioid receptor modulator*, contributing to its antitussive effect.
- Guaifenesin
- Exerts *mucolytic activity* by reducing airway mucus viscosity, facilitating expectoration.
- Induces *augmented bronchial secretions* and enhances sputum clearance through increased ciliary motility.
- Other Active Ingredients (if present)
- *Diphenhydramine*: antagonises H1 receptors, decreasing histamine‑mediated cough and wheeze.
- *Benzydamine*: non‑steroidal anti‑inflammatory; reduces airway irritation.
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Pharmacokinetics
| Parameter | Key Points | Notes |
| Absorption | Rapid oral absorption; peak plasma concentrations within 15–60 min. | Bioavailability ~30–40 % for DM due to first‑pass metabolism. |
| Distribution | Widely distributed; cross‑blood‑brain barrier. | Volume of distribution ~1.5 L/kg for DM. |
| Metabolism | Predominantly hepatic via CYP2E1 (DM) and CYP1A2 (guaifenesin). | Genetic polymorphisms influence DM clearance (slow vs fast metabolizers). |
| Excretion | Renal excretion of metabolites mostly; <5% unchanged drug. | Clearance: 12–14 L/h in adults. |
| Half‑life | DM: 3–5 h; Guaifenesin: 5–8 h. | Accumulates with frequent dosing; monitor for CNS effects. |
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Indications
- Acute Dry (Non‑productive) Cough
- *Robitussin DM* or *Robitussin DM with antiallergic* for post‑viral cough.
- Productive (Wet) Cough
- *Robitussin HC* (guaifenesin) for clearing mucus in bronchitis, sinusitis, or COPD exacerbations.
- Cough‑with‑Fever or Congestion
- *Robitussin CF* (DM + decongestant + antipyretic) for colds.
- Post‑Operative Cough or Asthma‑Related Cough
- When combined with bronchodilator rescue (respectful of local guidelines).
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Contraindications
- Contraindicated
- Severe CNS depression or hypersensitivity to DM or guaifenesin.
- Elderly or debilitated patients with impaired hepatic function (prolonged DM activity).
- Pregnancy: Formulation with DM classified as *Category B*; use cautiously; prefer milder expectorants if possible.
- Breastfeeding: Both DM and guaifenesin may pass into milk; discontinue if clinically required.
- Warnings
- CNS depression: risk of dizziness, somnolence, or respiratory depression in high doses or with alcohol.
- Drug interactions:
- MAO inhibitors or CNS depressants (benzodiazepines, opioids) amplify DM effects.
- CYP2E1 inhibitors (e.g., chlorothalonil) increase DM plasma levels.
- Idiosyncratic reactions: rare anaphylaxis, photosensitivity.
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Dosing
| Formulation | Adult Dose | Pediatric Dose | Frequency |
| Robitussin DM (10 mg/mL) | 10 mg (1 mL) *every 4–6 h*; max 60 mg/24 h | 0.5 mg/kg *every 4–6 h*; max 30 mg/24 h | PRN |
| Robitussin HC (200 mg/mL) | 200 mg (1 mL) *every 4–6 h*; max 800 mg/24 h | 10 mg/kg *every 4–6 h*; max 400 mg/24 h | PRN |
| Robitussin CF (cough+fever) | 5 mL *every 6 h* for adults; add decongestant portion | 0.5 mL/kg * *every 6 h* | PRN |
| Robitussin DM + Diphenhydramine (DM 10 mg, Diphenhydramine 4.5 mg/mL) | 4.5 mL (DM 45 mg) *every 6 h*; max 180 mg/24 h | 0.45 mg/kg *every 6 h*; max 90 mg/24 h | PRN |
• Administration
• Use a calibrated oral syringe or dosing cup.
• Shake well before each dose.
• Administer with food or water to reduce GI discomfort.
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Adverse Effects
- Common
- Dizziness, somnolence, mild nausea.
- Dry mouth (more frequent with DM).
- Muscle aches or mild headache.
- Serious
- CNS depression → respiratory arrest *in overdose*.
- Visual disturbances (blurred vision).
- Allergic reactions: rash, urticaria, anaphylaxis (rare).
- Impaired liver function in chronic use or high doses.
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Monitoring
- Baseline
- Liver function tests (ALT/AST) if chronic use or hepatic impairment.
- Respiratory status in patients with COPD or asthma.
- During Use
- Assess for CNS depression: check alertness, ventilation rate.
- Monitor weight and hydration if using decongestant variants.
- Evaluate improvement in cough severity; consider tapering if resolution.
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Clinical Pearls
1. Dual‑action benefit: Use Robitussin DM for cough suppression *before* using Robitussin HC for mucus clearance to avoid *excessive bronchodilation* that might worsen cough reflex.
2. Drug‑Herb Interaction: Herbal supplements like St. John’s Wort induce CYP2E1, reducing DM efficacy; advise patients to avoid concurrent use.
3. Avoid concurrent alcohol: Alcohol potentiates CNS depression; counsel patients to delay or reduce alcohol intake during therapy.
4. Pediatric dosing: Use weight‑based calculations; the maximum pediatric dose is typically 30 mg/24 h for DM, 400 mg/24 h for HC.
5. Pregnancy & Lactation: While DM is Category B, choose guaifenesin alone when possible to minimize fetal exposure.
6. Withdrawal vs Tolerance: Cough suppression is short‑term; chronic use can yield tolerance; avoid >2 weeks of continuous DM therapy.
7. Guaifenesin’s Efficacy: Only modest; best combined with saline inhalation or steam therapy for, e.g., bronchial inflammation.
8. Patient Education: Clarify that “cough syrup” is not a cure for underlying respiratory disease; treat the underlying cause (e.g., infection, COPD) concurrently.
9. Contact Red Flag: Immediate medical attention if the patient experiences reduced breathing, black vomitus (possible overdose), or severe rash.
10. Pharmacogenomics: *CYP2E1* slow metabolizers may exhibit prolonged DM action (24 h). Consider genotyping in chronic cough management.
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• References
To maintain up‑to‑date accuracy, consult the official product literature, FDA drug labeling, and peer‑reviewed pharmacology texts (e.g., *Goodman & Gilman’s The Pharmacological Basis of Therapeutics*, *Harrison’s Principles of Internal Medicine*).