Usage
Ranitidine is prescribed for the treatment and prevention of various conditions related to excess stomach acid production. These include:
- Gastroesophageal Reflux Disease (GERD): A chronic digestive disease where stomach acid flows back into the esophagus, causing heartburn and other symptoms.
- Peptic Ulcers: Sores that develop in the lining of the stomach or duodenum (the first part of the small intestine).
- Zollinger-Ellison Syndrome: A rare condition characterized by tumors in the pancreas or duodenum that produce excessive amounts of gastrin, a hormone that stimulates stomach acid secretion.
- Stress Ulcer Prophylaxis: Prevention of ulcers in critically ill patients.
- Indigestion and Heartburn: Relief of occasional symptoms of heartburn and indigestion.
- Erosive Esophagitis: Inflammation and damage to the esophagus caused by stomach acid reflux.
Pharmacological Classification: Ranitidine belongs to the class of histamine H2-receptor antagonists (H2 blockers).
Mechanism of Action: Ranitidine competitively inhibits the binding of histamine to H2 receptors in the parietal cells of the stomach. This reduces the production of stomach acid.
Alternate Names
Ranitidine is the generic name. Brand names include Zantac, R-Loc, Ranitil, and others. There are no significant international or regional variations in the generic name. Zantac was a popular brand name but is currently unavailable in many countries.
How It Works
Pharmacodynamics: Ranitidine reduces the volume and acidity of gastric secretions. Its effects are dose-dependent.
Pharmacokinetics:
- Absorption: Ranitidine is well-absorbed after oral administration, with peak plasma concentrations reached in 1-3 hours.
- Metabolism: Ranitidine undergoes minimal first-pass metabolism in the liver.
- Elimination: Primarily eliminated by the kidneys (renal excretion), with about 30% of an oral dose and 70% of an intravenous dose excreted unchanged in the urine within 24 hours. It also undergoes hepatic metabolism to a small extent.
Mode of Action: Ranitidine competitively binds to H2 receptors on the basolateral membrane of parietal cells. This blocks histamine’s stimulatory effect on these receptors, thereby reducing the activation of adenylate cyclase, decreasing intracellular cyclic AMP levels, and ultimately lowering acid secretion.
Receptor Binding/Enzyme Inhibition: Ranitidine’s primary action is competitive antagonism of the H2 receptor. It does not significantly inhibit CYP450 enzymes, though some drug interactions can occur.
Dosage
Standard Dosage
Adults:
- Oral: 150 mg twice daily or 300 mg once daily at bedtime. Dosages up to 600 mg daily have been used for some conditions.
- Intravenous (IV): 50 mg every 6-8 hours. Alternatively, a continuous infusion of 6.25 mg/hour can be administered.
- Intramuscular (IM): 50 mg every 6-8 hours.
Children (1 month to 16 years):
- Oral: 2-4 mg/kg twice daily (maximum 300 mg/day) or 2 to 4 mg/kg once daily at bedtime.
- IV: 2-4 mg/kg/day divided every 6-8 hours (maximum 50 mg/dose).
Infants (under 1 month):
Dosing should be determined by a neonatologist or pediatrician experienced in neonatal care. Dosages will be weight-based, and IV administration is preferred.
Special Cases:
- Elderly Patients: Start at the lowest recommended dose and adjust based on renal function. Close monitoring is recommended.
- Patients with Renal Impairment: Dosage adjustment is required based on creatinine clearance (CrCl). For CrCl < 50 mL/min, the oral dose may be reduced to 150 mg at night. For IV or IM administration, a dose reduction may also be necessary.
- Patients with Hepatic Dysfunction: No specific dosage adjustments are typically necessary but caution is recommended.
- Patients with Comorbid Conditions: Dose adjustment may be required based on the specific comorbid condition.
Clinical Use Cases
The standard adult dosages as mentioned above apply to most clinical use cases. For intubation, surgical procedures, mechanical ventilation, ICU use, and emergency situations, IV administration is typically preferred for more rapid onset of action and better control of dosage.
Dosage Adjustments:
Adjustments are required based on renal function, age, and specific clinical response. Therapeutic drug monitoring may be helpful in certain situations to optimize dosage.
Side Effects
Common Side Effects:
- Headache
- Constipation
- Diarrhea
- Nausea
- Abdominal pain
- Dizziness
Rare but Serious Side Effects:
- Hepatitis
- Pancreatitis
- Blood disorders (e.g., leukopenia, thrombocytopenia)
- Confusion
- Hallucinations
- Bradycardia (with rapid IV administration)
Long-Term Effects:
- Potential for Vitamin B12 deficiency with prolonged use
Adverse Drug Reactions (ADR):
- Hypersensitivity reactions (rare)
- Stevens-Johnson syndrome (very rare)
Contraindications
- Hypersensitivity to ranitidine or other H2 blockers.
- Porphyria.
Drug Interactions
Ranitidine can interact with several medications, including:
- Antacids (may decrease ranitidine absorption)
- Ketoconazole, itraconazole (may reduce absorption of these antifungals)
- Warfarin (may enhance anticoagulant effects)
- Midazolam, triazolam (may increase levels of these benzodiazepines)
- Procainamide (may increase procainamide levels)
Pregnancy and Breastfeeding
- Pregnancy Safety Category: Ranitidine was previously categorized as Pregnancy Category B (no evidence of risk in humans), however, due to potential contamination with NDMA (N-Nitrosodimethylamine) the use during pregnancy is only recommended when clearly needed.
- Breastfeeding: Ranitidine is excreted in breast milk. While generally considered compatible with breastfeeding, due to the potential for NDMA contamination alternatives might be considered. The decision to use ranitidine during breastfeeding should be made in consultation with a healthcare professional.
Drug Profile Summary
- Mechanism of Action: H2 receptor antagonist, reducing gastric acid secretion.
- Side Effects: Headache, constipation, diarrhea, nausea, abdominal pain, dizziness; rarely, serious blood disorders, liver inflammation, or confusion.
- Contraindications: Hypersensitivity to ranitidine or other H2 blockers, porphyria.
- Drug Interactions: Antacids, ketoconazole, warfarin, midazolam, triazolam, procainamide.
- Pregnancy & Breastfeeding: Caution advised. Discuss risks and benefits with a physician.
- Dosage: Adults: 150 mg twice daily or 300 mg once daily. Children: 2-4 mg/kg twice daily. IV/IM dosages available.
- Monitoring Parameters: Renal function, liver function tests (if indicated), complete blood count (if indicated).
Popular Combinations
Ranitidine is often used in combination with antacids for symptom relief, although administration should be separated by at least one hour. In cases of H. pylori infection, ranitidine may be combined with antibiotics such as clarithromycin and amoxicillin.
Precautions
- Pre-existing liver or kidney disease.
- Chronic lung disease.
- Diabetes.
- Immunocompromised states.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Ranitidine?
A: Adults: 150 mg twice daily or 300 mg once daily. Children: 2-4 mg/kg twice daily. IV/IM options available. Dosage adjustments necessary for renal impairment and other special populations.
Q2: What are the common side effects of Ranitidine?
A: Common side effects include headache, constipation, diarrhea, nausea, and abdominal pain.
Q3: Is Ranitidine safe during pregnancy?
A: Due to the potential for NDMA contamination its use is only recommended if clearly needed. Consult a physician to discuss the risks and benefits.
Q4: Can I take Ranitidine while breastfeeding?
A: Ranitidine is excreted in breast milk, but usually at low levels. Due to the potential for NDMA contamination, alternatives may be preferable. Discuss with your doctor.
Q5: How does Ranitidine work?
A: It blocks H2 receptors in the stomach, reducing acid production.
Q6: What are the contraindications for Ranitidine?
A: Contraindications include hypersensitivity to ranitidine or other H2 blockers and porphyria.
Q7: Does Ranitidine interact with other medications?
A: Yes, it can interact with antacids, ketoconazole, warfarin, and certain other medications.
Q8: What should I monitor in patients taking Ranitidine?
A: Monitor renal and liver function and perform blood counts if clinically indicated.
Q9: Can Ranitidine be used for long-term treatment?
A: Yes, but long-term use may be associated with vitamin B12 deficiency.
