1. Clinical Overview
A fixed-dose combination (FDC) of a selective calcium channel blocker (Cinnarizine) and a first-generation ethanolamine antihistamine (Dimenhydrinate). It is primarily used for the prophylaxis and treatment of vestibular vertigo and motion sickness. Cinnarizine acts by improving labyrinthine and cerebral blood flow and reducing vestibular excitability, while Dimenhydrinate provides central antiemetic and sedative effects via H1-antagonism and anticholinergic action. This combination offers a synergistic effect for managing vertigo and associated nausea/vomiting, making it a widely prescribed formulation in India for conditions like Ménière's disease and motion sickness.
| Onset | Duration | Bioavailability |
|---|---|---|
| Oral: 30 to 60 minutes. | Approximately 4 to 6 hours. | Cinnarizine: ~80-90%. Dimenhydrinate: Dimenhydrinate is a salt of diphenhydramine and 8-chlorotheophylline; diphenhydramine bioavailability is ~40-60%. |
2. Mechanism of Action
The combination exerts a dual mechanism. Cinnarizine is a selective calcium channel blocker that inhibits calcium influx into vascular smooth muscle cells and labyrinthine arterial cells, leading to vasodilation. This improves microcirculation in the inner ear (labyrinth) and brain. It also reduces the excitability of vestibular sensory cells and inhibits vestibular nuclei. Dimenhydrinate is a salt of diphenhydramine (an H1-antagonist) and 8-chlorotheophylline (a mild CNS stimulant). Its primary action is antagonism of histamine H1 receptors in the vomiting center and the vestibular pathway. It also possesses significant antimuscarinic (anticholinergic) activity, which further depresses vestibular stimulation and labyrinthine excitability. The combination provides synergistic control of vertigo, nausea, and vomiting.
3. Indications & Uses
- Prophylaxis and treatment of Vertigo (especially of vestibular origin e.g., Ménière's disease, labyrinthitis)
- Prophylaxis and treatment of Motion Sickness (travel sickness)
4. Dosage & Administration
Adult Dosage: One tablet (Cinnarizine 20mg + Dimenhydrinate 40mg) three times daily. For motion sickness prophylaxis: One tablet 30 minutes before travel, may repeat every 4-6 hours as needed (max 3 tablets in 24 hours).
Administration: Administer orally with or without food. Taking with food may reduce gastric irritation. Tablet should be swallowed whole with a glass of water. For motion sickness, take at least 30 minutes before exposure to motion.
5. Side Effects
Common side effects may include:
- Drowsiness/Sedation
- Dry mouth
- Fatigue
- Headache
- Gastrointestinal discomfort (dyspepsia)
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| CNS Depressants (Alcohol, Benzodiazepines, Opioids, Barbiturates) | Additive CNS depression, increased sedation, impaired psychomotor performance. | Major |
| Anticholinergic Drugs (Atropine, TCAs, Antipsychotics like clozapine) | Additive anticholinergic effects (dry mouth, constipation, urinary retention, blurred vision, confusion). | Major |
| MAO Inhibitors (Phenelzine, Tranylcypromine) | Increased anticholinergic and CNS depressant effects. Risk of hypertensive crisis. | Major |
| Other Antihypertensives | Potentiation of hypotensive effect. | Moderate |
| CYP2D6 Inhibitors (Fluoxetine, Paroxetine, Quinidine) | Increased plasma levels of both drugs, leading to enhanced effects and toxicity. | Moderate |
| Warfarin | Potential increased anticoagulant effect (theoretical). Monitor INR. | Moderate |
7. Patient Counselling
- DO take the tablet as prescribed, usually 30 minutes before travel for motion sickness.
- DO inform your doctor about all other medicines, including over-the-counter drugs and herbal supplements.
- DO NOT consume alcohol while on this medication.
- DO NOT drive, operate heavy machinery, or engage in activities requiring mental alertness.
- DO NOT take a double dose to make up for a missed one.
- DO inform your doctor if you are pregnant, planning pregnancy, or breastfeeding.
8. Toxicology & Storage
Overdose: Symptoms are primarily an extension of side effects: Severe CNS depression (coma, respiratory depression), profound anticholinergic effects (hyperthermia, flushed dry skin, dilated pupils, tachycardia, urinary retention, ileus), seizures (especially in children), hallucinations, cardiovascular collapse, and arrhythmias.
Storage: Store in a cool, dry place, protected from light and moisture. Keep at room temperature (below 30°C). Keep out of reach of children. Do not use after the expiry date printed on the pack.