1. Clinical Overview
A fixed-dose combination antitussive and expectorant syrup. Diphenhydramine is a first-generation ethanolamine-class antihistamine with potent anticholinergic and sedative properties, providing cough suppression via central action on the medullary cough center. Ammonium Chloride acts as an expectorant by irritating the gastric mucosa, leading to a reflex increase in respiratory tract secretions, thereby reducing sputum viscosity. Sodium Citrate acts as an alkalizing agent and systemic expectorant, increasing the pH of respiratory secretions and bronchial fluid, making them less viscous and easier to expel. This combination is primarily indicated for the symptomatic relief of dry, non-productive cough associated with upper respiratory tract infections, common cold, and allergic conditions.
| Onset | Duration | Bioavailability |
|---|---|---|
| Diphenhydramine: 15-30 minutes; Ammonium Chloride & Sodium Citrate: 30-60 minutes. | Diphenhydramine: 4-6 hours; Expectorant effect: 3-4 hours. | Diphenhydramine: ~40-60% (oral); Ammonium Chloride: Rapidly absorbed; Sodium Citrate: Well absorbed. |
2. Mechanism of Action
The combination works via three distinct mechanisms. 1) Diphenhydramine suppresses cough by a central action, depressing the cough center in the medulla oblongata. Its antihistaminic action also helps alleviate allergic components of cough. 2) Ammonium Chloride acts as a nauseant expectorant. After oral administration, it causes mild irritation of the gastric mucosa, which stimulates the vagal afferent nerves. This triggers a reflex via the medullary centers to increase the output of fluid by the bronchial glands, thereby thinning tenacious mucus. 3) Sodium Citrate, when absorbed, is metabolized to sodium bicarbonate, alkalinizing the blood and respiratory tract secretions. This change in pH reduces the viscosity of bronchial secretions, facilitating their removal.
3. Indications & Uses
- Symptomatic relief of dry, non-productive (tickly) cough
- Cough associated with upper respiratory tract infections (common cold, pharyngitis)
- Allergic cough
4. Dosage & Administration
Adult Dosage: 10 ml (2 teaspoonfuls) three to four times daily. Maximum: 40 ml per day.
Administration: To be taken orally. Use the measuring cup or spoon provided. Can be taken with or without food. Taking with food may reduce gastric irritation from ammonium chloride. Drink a full glass of water after each dose to aid expectorant action. Do not drive or operate machinery for 4-6 hours after a dose.
5. Side Effects
Common side effects may include:
- Drowsiness, sedation, sleepiness
- Dry mouth, nose, and throat
- Dizziness
- Gastrointestinal upset (nausea, epigastric discomfort)
- Thickening of bronchial secretions (paradoxical)
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Alcohol, Benzodiazepines, Opioids, other CNS Depressants | Additive CNS depression, increased risk of sedation, respiratory depression, and impaired psychomotor performance. | Major |
| Monoamine Oxidase Inhibitors (MAOIs) e.g., Phenelzine, Selegiline | Potentiation of anticholinergic effects (hyperpyrexia, hypertension, seizures). | Contraindicated |
| Anticholinergic drugs (e.g., Atropine, Tricyclic Antidepressants, Antipsychotics) | Additive anticholinergic side effects (dry mouth, urinary retention, constipation, tachycardia, confusion). | Major |
| Drugs metabolized by CYP2D6 (e.g., Codeine, Metoprolol, Flecainide) | Diphenhydramine may inhibit CYP2D6, increasing plasma levels of these drugs. | Moderate |
| Urinary Alkalinizers (e.g., Acetazolamide, Sodium Bicarbonate) | May reduce renal excretion of diphenhydramine, increasing its levels and effects. | Moderate |
| Antihypertensives | Diphenhydramine may counteract the effect of some antihypertensives and cause tachycardia. | Moderate |
7. Patient Counselling
- DO take the exact dose as prescribed by your doctor.
- DO use the measuring device provided with the syrup.
- DO drink plenty of water/fluids while taking this medicine to help loosen mucus.
- DO NOT drive, operate machinery, or perform hazardous tasks for at least 4-6 hours after a dose.
- DO NOT consume alcohol or other sedative medications while on this therapy.
- DO NOT take it for chronic cough without consulting a doctor.
- DO NOT give this medicine to children under 2 years of age.
- DO NOT take it if you are pregnant or breastfeeding without medical advice.
8. Toxicology & Storage
Overdose: Anticholinergic Toxidrome: Severe CNS depression (coma, respiratory depression) or paradoxical CNS stimulation (hallucinations, seizures). Other symptoms: fixed dilated pupils, flushing, hyperthermia, tachycardia, hypertension followed by hypotension, urinary retention, dry mouth. In severe cases: rhabdomyolysis, cardiac arrhythmias, and death.
Storage: Store at room temperature (15-25°C), protected from light and moisture. Keep the bottle tightly closed. Keep out of reach and sight of children. Do not use after the expiry date printed on the label. Do not freeze.