A fixed-dose combination (FDC) of Ondansetron, a selective 5-HT3 receptor antagonist, and Ranitidine, a histamine H2-receptor antagonist. This combination provides synergistic antiemetic and gastroprotective effects by targeting both the chemoreceptor trigger zone (CTZ) and gastric acid secretion. It is primarily used for the prevention and treatment of nausea and vomiting associated with chemotherapy, radiotherapy, and postoperative recovery, while also preventing stress ulceration and acid reflux. The FDC is widely used in Indian clinical practice, especially in oncology and surgical settings, though its regulatory status has been scrutinized by the Indian drug regulatory authority.
Adult: Typically, one tablet twice daily. Common strengths: Ondansetron 4 mg + Ranitidine 150 mg or Ondansetron 8 mg + Ranitidine 300 mg. For Chemotherapy: Ondansetron 8 mg + Ranitidine 150 mg twice daily, starting before chemotherapy. For PONV: Single dose preoperatively or postoperatively. Maximum daily dose of Ondansetron: 24 mg (as per most guidelines).
Note: Tablets: Swallow whole with a glass of water, with or without food. To prevent chemotherapy-induced nausea/vomiting, take the first dose 30-60 minutes before the start of chemotherapy. For postoperative use, administer 1 hour before anesthesia. Do not crush or chew unless specified (e.g., dispersible).
The combination works via two distinct pathways. Ondansetron selectively blocks serotonin (5-HT3) receptors centrally in the chemoreceptor trigger zone (CTZ) of the area postrema and peripherally on vagal nerve terminals in the gastrointestinal tract, inhibiting the vomiting reflex. Ranitidine competitively inhibits histamine at H2 receptors of gastric parietal cells, leading to a marked reduction in basal and stimulated gastric acid secretion, volume, and hydrogen ion concentration. The combined action provides comprehensive management of nausea/vomiting while protecting the esophageal and gastric mucosa from acid-related damage, which is common during chemotherapy or post-surgery.
Pregnancy: Ondansetron: Category B (US FDA). Epidemiological studies show no clear increased risk of major malformations, but some data suggest a small increased risk of oral clefts. Use only if clearly needed and benefit justifies potential risk. Ranitidine: Category B (US FDA). Considered relatively safe, but long-term use not recommended. The FDC should be avoided in pregnancy unless no safer alternative exists and the condition is severe (e.g., hyperemesis gravidarum).
Driving: May cause dizziness, drowsiness, or blurred vision in some individuals. Patients should not drive or operate machinery until they know how the medication affects them.
| Apomorphine | Profound hypotension and loss of consciousness. | Contraindicated |
| Drugs prolonging QT interval (e.g., Class IA/III antiarrhythmics, macrolides, fluoroquinolones) | Additive risk of QT prolongation and cardiac arrhythmias. | Major |
| Phenytoin, Carbamazepine, Rifampicin | Induce CYP450 enzymes, reducing plasma concentration of ondansetron. | Moderate |
| CYP2D6 inhibitors (e.g., Fluoxetine, Quinidine) | May increase ondansetron concentration. | Moderate |
| Antacids, Sucralfate | May reduce absorption of ranitidine; administer at least 2 hours apart. | Moderate |
| Warfarin | Ranitidine may alter warfarin metabolism; monitor INR closely. | Moderate |
| Midazolam, Triazolam | Ranitidine may decrease hepatic metabolism, increasing their effect. | Moderate |
| Procainamide | Ranitidine may reduce renal clearance of procainamide, increasing toxicity risk. | Moderate |
| Dopamine agonists (e.g., Bromocriptine) | Ondansetron may antagonize the therapeutic effect. | Moderate |
Same composition (Ondansetron (NA) + Ranitidine (NA)), different brands: