1. Clinical Overview
A fixed-dose combination (FDC) antitussive, expectorant, and antihistamine used for symptomatic relief of cough and associated symptoms of upper respiratory tract infections (URTIs) and allergic conditions. Guaifenesin promotes mucus clearance, Dextromethorphan suppresses the cough reflex centrally, and Chlorpheniramine provides antihistaminic and mild sedative effects.
| Onset | Duration | Bioavailability |
|---|---|---|
| Guaifenesin: 15-30 minutes; Chlorpheniramine: 30-60 minutes; Dextromethorphan: 15-30 minutes. | Guaifenesin: 4-6 hours; Chlorpheniramine: 4-6 hours; Dextromethorphan: 5-6 hours. | Guaifenesin: ~45-60%; Chlorpheniramine: ~25-50%; Dextromethorphan: ~11% (extensive first-pass metabolism). |
2. Mechanism of Action
Guaifenesin enhances the output of respiratory tract fluid by reducing the adhesiveness and surface tension of secretions, facilitating mucus clearance. Dextromethorphan is a d-isomer of the codeine analog, levorphanol, and acts as a non-competitive NMDA receptor antagonist and sigma-1 receptor agonist. It raises the threshold for coughing in the cough center of the medulla without causing respiratory depression. Chlorpheniramine is a competitive reversible H1-receptor antagonist, inhibiting histamine-mediated symptoms and providing anticholinergic and sedative effects.
3. Indications & Uses
- Symptomatic relief of dry or non-productive cough associated with common cold
- Symptomatic relief of cough associated with allergic rhinitis
4. Dosage & Administration
Adult Dosage: 1-2 tablets/capsules/5ml syrup every 4-6 hours. Maximum: 4 doses in 24 hours.
Administration: Oral administration. Can be taken with or without food. Take with a full glass of water to aid expectorant action of Guaifenesin. Do not crush or chew sustained-release formulations if any. Syrup should be measured using the provided measuring cup or spoon.
5. Side Effects
Common side effects may include:
- Drowsiness/Sedation
- Dry mouth, nose, or throat
- Dizziness
- Gastrointestinal upset (nausea)
- Thickening of bronchial secretions
- Headache
- Fatigue
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Monoamine Oxidase Inhibitors (MAOIs) - Phenelzine, Tranylcypromine | Risk of severe serotonin syndrome, hyperpyrexia, hypertension, death. | Contraindicated |
| Selective Serotonin Reuptake Inhibitors (SSRIs) - Fluoxetine, Paroxetine | Increased risk of serotonin syndrome due to CYP2D6 inhibition and additive serotonergic effect. | Major |
| Other CNS Depressants - Alcohol, Benzodiazepines, Opioids, Sedating Antihistamines | Additive CNS depression, impaired alertness, increased risk of accidents. | Major |
| Anticholinergic Drugs - Atropine, Tricyclic Antidepressants, Antipsychotics | Additive anticholinergic side effects (dry mouth, constipation, urinary retention, blurred vision). | Moderate |
| CYP2D6 Inhibitors - Quinidine, Terbinafine | Increased plasma levels of Dextromethorphan and Chlorpheniramine, leading to increased effects/toxicity. | Moderate |
| Antihypertensives | Chlorpheniramine may reduce the effect of some antihypertensives. | Moderate |
7. Patient Counselling
- DO take with a full glass of water.
- DO measure syrup dose accurately.
- DO inform your doctor if you are taking any other medicines.
- DO NOT exceed the recommended dose or frequency.
- DO NOT drive or operate heavy machinery after taking this medicine.
- DO NOT consume alcohol.
- DO NOT use for chronic cough associated with smoking, asthma, or emphysema.
- DO NOT give to children under 2 years.
8. Toxicology & Storage
Overdose: Symptoms are primarily an extension of side effects: Severe CNS depression (somnolence, coma, respiratory depression) or stimulation (hallucinations, seizures, hyperexcitability especially in children). Anticholinergic toxidrome: flushed skin, dry mucous membranes, dilated pupils, tachycardia, hyperthermia, urinary retention. Nausea, vomiting. Severe overdose can lead to cardiac arrhythmias, hypotension, and death.
Storage: Store at room temperature (15-30°C), protected from light and moisture. Keep the bottle tightly closed. Keep out of reach of children. Do not freeze the syrup. Discard unused medicine after the expiry date.