Introduction
Ranitidine is a commonly used drug, classified as a histamine H2-receptor antagonist, and belongs to the same drug class as cimetidine and famotidine. This drug helps to prevent and treat gastric-acid associated conditions, including ulcers, because of its ability to decrease gastric acid secretion. Ranitidine is often referred to as Zantac, and is available in various forms, including tablet, injection, and effervescent tablet preparations.
The prevalence of GERD is thought to be 10-20% in western countries. Ranitidine has proven to be an effective treatment for relieving uncomfortable symptoms of gastric acid associated conditions and is therefore widely used in GERD and other gastric-acid related conditions.
Uses
Ranitidine is a histamine H2 antagonist used to treat duodenal ulcers, Zollinger-Ellison syndrome, gastric ulcers, GERD, and erosive esophagitis.
This drug is used alone or with concomitant antacids for the following conditions: short-term treatment of active duodenal ulcer, treating gastric acid hypersecretion due to Zollinger-Ellison syndrome, systemic mastocytosis, and other conditions that may pathologically raise gastric acid levels. It also used in the short term treatment of active benign gastric ulcers and maintenance therapy of gastric ulcers at a reduced dose. In addition to the above, ranitidine can be used for the treatment of GERD symptoms, treatment of erosive esophagitis (endoscopically diagnosed) and the maintenance of gastric or duodenal ulcer healing.
Associated Conditions
Pharmacodynamics
Ranitidine decreases the secretion of gastric acid stimulated by food and drugs. It also reduces the secretion of gastric acid in hypersecretory conditions such as Zollinger-Ellison syndrome. Marked improvements in the appearance of the esophageal tissues have been observed by endoscopic imaging after ranitidine therapy.
Mechanism of Action
After a meal, the hormone gastrin, produced by cells in the lining of the stomach, stimulates the release of histamine, which then binds to histamine H2 receptors, leading to the secretion of gastric acid. Ranitidine reduces the secretion of gastric acid by reversible binding to histamine (H2) receptors, which are found on gastric parietal cells. This process leads to the inhibition of histamine binding to this receptor, causing the reduction of gastric acid secretion. The relief of gastric-acid related symptoms can occur as soon as 60 minutes after administration of a single dose, and the effects can last from 4-10 hours, providing fast and effective symptomatic relief.
Absorption
Ranitidine is rapidly absorbed with peak concentrations reached within 1-3 hours after administration, and varying greatly among patients. Bioavailability is about 50%-60% due to hepatic metabolism. In a pharmacokinetic study of healthy males, the AUC 0-infinity was about 2,488.6 ng x h/mL and the median Tmax was 2.83 hours. Food or antacids have limited effects on absorption. One clinical study found that the administration of a potent antacid (150 mmol) in subjects in the fasted state led to decreased absorption of ranitidine.
Volume of Distribution
The volume of distribution is higher than body volume, and measures at approximately 1.4 L/kg. It concentrates in breast milk, but does not readily distribute into the cerebrospinal fluid.
Protein Binding
The plasma protein binding of ranitidine is approximately 15%.
Route of Elimination
This drug is mainly excreted in the urine but also excreted in the feces. About 30% of a single oral dose has been measured in the urine as unchanged drug within 24 hours of ingestion.
Half Life
The elimination half-life or ranitidine is about 2.5-3 hours. It may be longer after oral administration versus injection. The plasma half-life is longer for elderly patients population due to a decrease in renal function, and is measured at 3-4 hours.
Clearance
Renal clearance is about 410 mL/min according to FDA prescribing information. Another resource mentions a plasma clearance of approximately 600 ml/min. Clearance is decreased in the elderly and those with impaired or hepatic renal function. It is recommended to decrease the dose of ranitidine by one-half in patients with renal impairment.
Toxicity
Oral doses of 1,000 mg/kg in mice and rats were not found to be lethal. Intravenous LD50 values in mice and rats were 77 and 83 mg/kg, respectively.
Overdose information
There has been limited experience with ranitidine overdose. Reported acute ingestions of up to 18 grams orally were followed by temporary adverse effects similar to the normal adverse effects of this drug, including tachycardia, bradycardia, dizziness, diarrhea, nausea, and vomiting, among other effects. Gait abnormalities and hypotension have also been observed. When an overdose with ranitidine is suspected, remove unabsorbed ranitidine from the gastrointestinal tract if possible, and monitor the patient and provide supportive therapy as required.
Food Interactions
- Take with or without food. The absorption is unaffected by food.
Dosage
Ranitidine Tablet & Syrup:
Duodenal and gastric ulcer: The usual dosage is 150 mg twice daily taken in the morning and evening or 300 mg as a single daily dose at night for 4 to 8 weeks.Reflux oesophagitis: 150 mg twice daily or 300 mg at bed time for up to 8 weeks.
Zollinger Ellison syndrome: 150 mg 3 times daily and increased if necessary up to 6 g daily in divided doses. Dosage should be continued as long as clinically indicated.
Episodic dyspepsia: 150 mg twice daily or 300 mg at bed time for up to 6 weeks.
Maintenance: 150 mg at night for preventing recurrences.
Child (peptic ulcer): 2-4 mg/kg twice daily, maximum 300 mg daily.
Ranitidine IV injection & IV Infusion:
Ranitidine injection may be given either as a slow (over a period of at least two minutes) intravenous injection of 50 mg, after dilution to a volume of 20 ml per 50 mg dose, which may be repeated every six to eight hours; or as an intermittent intravenous infusion at a rate of 25 mg per hour for two hours; the infusion may be repeated at six to eight hour intervals; or as an intramuscular injection of 50 mg (2 ml) every six to eight hours. In the prophylaxis of haemorrhage from stress ulceration in seriously ill patients or the prophylaxis of recurrent haemorrhage in patients bleeding from peptic ulceration, parenteral administration may be continued until oral feeding commences.In the prophylaxis of upper gastrointestinal haemorrhage from stress ulceration in seriously ill patient sapriming dose of 50 mg as low as intravenous injection followed by a continuous intravenous infusion of 0.125-0.250 mg/kg/hour may be preferred. In patients considered to be at risk of developing aspiration syndrome Ranitidine injection 50 mg may be given intramuscularly or by slow intravenous injection 45 to 60 minutes before induction of general anaesthesia.
Children: The recommended oral dose for the treatment of peptic ulcer in children is 2 mg/kg to 4 mg/kg twice daily to a maximum of 300 mg ranitidine per day. Safety and effectiveness of Ranitidine injection have not been established in case of children.
