H2 Antagonist (Ranitidine)

Summary

In this video, Yamant Pant provides a detailed explanation of ranitidine, an H2 antagonist used to reduce stomach acid production. He covers its history, mechanism of action, pharmacokinetics, indications, contraindications, and common side effects. Ranitidine blocks histamine binding to H2 receptors, effectively managing conditions like GERD, gastric ulcers, and Zollinger-Ellison syndrome. Pant also discusses the drug's dosing, potential drug interactions, and precautions, noting its temporary withdrawal from the U.S. market in 2020 due to impurity-related hepatotoxicity concerns. The video offers a thorough understanding of ranitidine's clinical use and precautions for healthcare professionals and students.

Takeaways

• 😀 Ranitidine is an H2 antagonist that reduces stomach acid secretion by blocking histamine from binding to its receptors on gastric parietal cells.
• 😀 Ranitidine was initially withdrawn from the U.S. market in 2020 due to concerns over hepatotoxicity, but later reintroduced after confirming the issue was due to impurity levels.
• 😀 Ranitidine is available in various forms, including tablets (150 mg, 300 mg) and injections (25 mg/ml), with multiple brands on the market like Zyntak, Rantac, and Estelog.
• 😀 The drug has a bioavailability of 50-60%, meaning only a portion of the oral dose reaches the bloodstream. Peak plasma concentrations occur within 1-3 hours of oral administration.
• 😀 The primary metabolism of ranitidine occurs in the liver, and it is excreted through urine, with a plasma half-life of 2.5-3 hours, which may be extended in elderly patients.
• 😀 Ranitidine works by inhibiting the action of histamine at H2 receptors, which in turn reduces gastric acid secretion, helping conditions like ulcers and GERD.
• 😀 Common clinical indications for ranitidine include gastric ulcers, gastroesophageal reflux disease (GERD), Zollinger-Ellison Syndrome (ZES), and duodenal ulcers.
• 😀 Ranitidine should not be used in patients with a history of acute porphyria, a condition that impairs the body's ability to convert porphyrins into heme.
• 😀 Common adverse effects include headache, dizziness, confusion, hypersensitivity reactions, and in rare cases, hallucinations, especially in elderly patients.
• 😀 Drug interactions with ranitidine may include decreased absorption of other drugs like ketoconazole, and smoking may reduce the drug’s plasma levels, requiring dose adjustments.
• 😀 In patients with renal impairment (creatinine clearance < 50 mL/min), the dosage of ranitidine should be reduced, but no dosage adjustment is needed for those with liver impairment.

Q & A

What is Ranitidine and what is its primary function?

Ranitidine is an H2 receptor antagonist used primarily to reduce stomach acid production. It works by blocking histamine from binding to the H2 receptors in the parietal cells of the stomach, thereby decreasing the secretion of gastric acid.

What was the reason for Ranitidine being withdrawn from the U.S. market in 2020?

Ranitidine was withdrawn from the U.S. market in April 2020 due to concerns over a contaminant that could cause liver toxicity. However, it was later determined that the toxicity was due to an impurity in the formulation, and the drug has since returned to the market.

What are the typical dosages of Ranitidine for common conditions?

For gastric ulcers, the usual dose is 150 mg every 6 hours or 50 mg IM/IV every 6 to 8 hours. For hypersecretory conditions, doses can go up to 6 grams per day, with a maximum of 400 mg per day intravenously or intramuscularly.

What are the common side effects associated with Ranitidine?

Common side effects of Ranitidine include headache, dizziness, confusion, and hallucinations. It can also cause rare side effects such as hepatotoxicity, pancreatitis, joint pain, and muscle pain.

How does Ranitidine interact with other drugs or substances?

Ranitidine can interact with antacids, which may reduce its absorption due to changes in the gastric pH. It can also interact with ketoconazole, reducing its absorption, and smoking can decrease the plasma levels of Ranitidine, potentially reducing its effectiveness.

What is the mechanism of action of Ranitidine in the stomach?

Ranitidine works by inhibiting the binding of histamine to H2 receptors in the parietal cells of the stomach, which reduces the secretion of hydrochloric acid. This mechanism is particularly useful in treating conditions like acid reflux and ulcers.

What should be the dosage adjustments for Ranitidine in patients with kidney impairment?

In patients with renal impairment and creatinine clearance less than 50 mL/min, the dosage of Ranitidine should be reduced to avoid toxicity. The dosing frequency or amount should be adjusted based on the severity of kidney dysfunction.

Can Ranitidine be prescribed to pregnant or breastfeeding women?

Ranitidine is generally considered safe during pregnancy, but it should only be prescribed when necessary, with a careful risk-benefit analysis. It is not recommended during breastfeeding without medical advice due to limited data on its excretion in breast milk.

What is the bioavailability of Ranitidine, and how is it absorbed in the body?

Ranitidine has a bioavailability of 50-60% when taken orally. Its peak concentration in the bloodstream occurs within 1-3 hours after oral administration, and within 15 minutes when administered intramuscularly.

What precautions should be taken when administering Ranitidine to elderly patients?

In elderly patients, the half-life of Ranitidine can be prolonged due to decreased renal function. Therefore, the dosage should be reduced, and the patient should be monitored closely for any adverse effects, especially in those with renal or hepatic impairment.