1. Clinical Overview
Ranitidine is a competitive, reversible antagonist of histamine at the H2-receptors of the gastric parietal cells, leading to a marked reduction in gastric acid secretion (both basal and stimulated). It is a second-generation H2-receptor antagonist (H2RA) with greater potency and longer duration of action than cimetidine. The 75mg/5ml oral liquid formulation is commonly used for symptomatic relief in acid-related disorders, particularly in pediatric and geriatric populations or those with swallowing difficulties. Its use has been significantly restricted globally and in India following the 2019-2020 recalls due to contamination with the probable human carcinogen N-Nitrosodimethylamine (NDMA). In India, it is now available only under strict regulatory scrutiny for specific, short-term indications where alternatives are not suitable.
| Onset | Duration | Bioavailability |
|---|---|---|
| Oral: 1-3 hours for peak acid suppression. | Approximately 12 hours for a single 75mg dose. | Approximately 50% (oral). Bioavailability is reduced by food and antacids. |
2. Mechanism of Action
Ranitidine competitively and reversibly inhibits the binding of histamine to the H2-receptors located on the basolateral membrane of gastric parietal cells. This blockade prevents the activation of adenylate cyclase, reducing intracellular cyclic AMP (cAMP) levels. The decrease in cAMP inhibits the activation of the proton pump (H+/K+ ATPase), leading to a significant reduction in both the volume and hydrogen ion concentration of gastric acid secretion. It suppresses basal (fasting) acid output, as well as acid secretion stimulated by food, histamine, pentagastrin, caffeine, and insulin.
3. Indications & Uses
- Symptomatic relief in heartburn, acid indigestion, and sour stomach (occasional use).
- Short-term treatment of active duodenal ulcer.
- Maintenance therapy for healed duodenal ulcer (at reduced dose).
- Treatment of benign gastric ulcer.
- Pathological hypersecretory conditions (e.g., Zollinger-Ellison syndrome).
4. Dosage & Administration
Adult Dosage: For symptomatic relief (Heartburn/Acid Indigestion): 75mg (5ml) dissolved in a glass of water, up to twice daily. Maximum: 150mg in 24 hours. Not to be used for more than 14 days continuously without medical advice. For active duodenal ulcer: 150mg twice daily or 300mg at bedtime. Maintenance: 150mg at bedtime.
Administration: Shake the bottle well before use. Use the measuring cup or oral syringe provided. The 5ml dose can be swallowed directly or mixed with a small amount of water (30-60ml) and drunk immediately. Can be taken with or without food, but for predictable absorption, take 1 hour before or 2 hours after meals. Do not take simultaneously with antacids; separate by at least 1 hour.
5. Side Effects
Common side effects may include:
- Headache
- Constipation
- Diarrhea
- Nausea/vomiting
- Abdominal discomfort
- Drowsiness/dizziness
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Warfarin | Ranitidine may slightly alter warfarin absorption; monitor INR as effect is variable. | Moderate |
| Midazolam, Triazolam | Ranitidine may increase bioavailability of these benzodiazepines, potentiating sedation. | Moderate |
| Procainamide | Ranitidine may reduce renal clearance of procainamide, increasing risk of toxicity. | Moderate |
| Glipizide, Glyburide | Ranitidine may potentiate hypoglycemic effect; monitor blood glucose. | Moderate |
| Ketoconazole, Itraconazole, Atazanavir | Ranitidine increases gastric pH, significantly reducing absorption of these pH-dependent drugs. Separate administration by at least 2 hours. | Major |
| Sucralfate | May decrease absorption of ranitidine. Administer ranitidine at least 2 hours before sucralfate. | Moderate |
| Antacids | May decrease absorption of ranitidine. Separate administration by at least 1 hour. | Minor |
7. Patient Counselling
- DO take the medicine exactly as prescribed or directed on the label.
- DO shake the bottle well before measuring each dose.
- DO use the provided measuring device (cup/syringe) for accuracy.
- DO inform your doctor if you are pregnant, planning pregnancy, or breastfeeding.
- DO inform your doctor about all other medicines, vitamins, and herbal supplements you are taking.
- DONT take the medicine for more than 14 days for self-treatable symptoms without consulting a doctor.
- DONT take a double dose to make up for a missed one.
- DUNT take antacids within 1 hour of taking ranitidine.
- DONT consume alcohol while on this medication.
8. Toxicology & Storage
Overdose: Symptoms are generally extensions of side effects: CNS effects (lethargy, dizziness, confusion, agitation, blurred vision), GI disturbances (nausea, vomiting), Bradycardia or tachycardia, Hypotension. Seizures have been reported with massive overdose.
Storage: Store at a temperature not exceeding 30°C, in a cool, dry place. Protect 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 the oral liquid.