1. Clinical Overview
A fixed-dose combination (FDC) of a selective 5-HT3 receptor antagonist (Ondansetron) and a histamine H2-receptor antagonist (Ranitidine). It provides synergistic antiemetic and gastroprotective action, primarily used for the prevention and treatment of nausea and vomiting associated with chemotherapy, radiotherapy, and postoperative recovery, while also reducing gastric acid secretion. This combination is particularly relevant in the Indian context for managing chemotherapy-induced nausea and vomiting (CINV) and post-operative nausea and vomiting (PONV) in patients with concomitant risk of acid-related disorders.
| Onset | Duration | Bioavailability |
|---|---|---|
| Ondansetron: Oral: 30-60 minutes; IV: Immediate. Ranitidine: Oral: 1-3 hours for acid suppression. | Ondansetron: 8-12 hours. Ranitidine: 8-12 hours for acid suppression. | Ondansetron: Approximately 60% (oral). Ranitidine: Approximately 50% (oral). |
2. Mechanism of Action
The combination works via two distinct pathways. Ondansetron selectively blocks serotonin (5-HT3) receptors peripherally (on vagal nerve terminals in the gastrointestinal tract) and centrally (in the chemoreceptor trigger zone of the area postrema). This blockade inhibits the vomiting reflex triggered by cytotoxic drugs and radiation. Ranitidine competitively inhibits histamine at H2 receptors of gastric parietal cells, leading to a reduction in basal and stimulated gastric acid secretion, volume, and hydrogen ion concentration.
3. Indications & Uses
- Prevention of nausea and vomiting associated with highly emetogenic cancer chemotherapy.
- Prevention of nausea and vomiting associated with radiotherapy.
- Prevention and treatment of post-operative nausea and vomiting (PONV).
4. Dosage & Administration
Adult Dosage: One tablet (Ondansetron 4mg + Ranitidine 50mg) two to three times daily, as directed by the physician. For chemotherapy: Often given 30 minutes before chemotherapy. Max: Ondansetron 24mg/day; Ranitidine 300mg/day.
Administration: Tablet can be taken with or without food. Swallow whole with a glass of water. For PONV prophylaxis, administer 1 hour before anesthesia. Do not crush or chew.
5. Side Effects
Common side effects may include:
- Headache
- Constipation
- Diarrhea
- Dizziness
- Drowsiness
- Local injection site reactions (if IV)
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Apomorphine | Profound hypotension and loss of consciousness. | Contraindicated |
| Drugs prolonging QT interval (e.g., Amiodarone, Sotalol, Moxifloxacin, Antipsychotics) | Additive risk of QT prolongation and cardiac arrhythmias. | Major |
| Phenytoin, Carbamazepine, Rifampicin | Induce CYP450 enzymes, reducing Ondansetron plasma levels. | Moderate |
| Cimetidine | May inhibit metabolism of Ondansetron, increasing its plasma concentration. | Moderate |
| Antacids, Sucralfate | Reduce absorption of Ranitidine. Administer at least 2 hours apart. | Moderate |
| Warfarin | Ranitidine may alter warfarin clearance; monitor INR. | Moderate |
| Midazolam, Triazolam | Ranitidine may decrease their metabolism, increasing sedation. | Moderate |
7. Patient Counselling
- Do take the tablet as prescribed, usually 30 minutes before chemotherapy or 1 hour before surgery.
- Do inform your doctor if you have a history of heart problems, liver disease, or kidney disease.
- Do not take with apomorphine.
- Do not crush or chew the tablet.
- Do inform your doctor of all other medicines you are taking, including over-the-counter drugs and herbal supplements.
8. Toxicology & Storage
Overdose: Manifestations may include sudden visual loss (Ondansetron), severe constipation, hypotension, dizziness, and acute agitation. ECG changes (QT prolongation, bradycardia) may occur.
Storage: Store below 30°C. Protect from light and moisture. Keep out of reach of children. Do not use after the expiry date printed on the pack.