Drug Class

H2 receptor antagonist (H2 blocker)
Antiulcer drug
Reduces gastric acid secretion

H2 receptors are present in:

• Stomach parietal cells

Brand Names

India:

• Rantac
• Aciloc
• Zinetac

USA

• Zantac (discontinued)

UK / Europe:

• Zantac

Approved By

• FDA (United States)
• CDSCO (India)
• EMA (Europe)

⚠️ Note: Ranitidine has been withdrawn or restricted in many countries due to NDMA impurity concerns.

Available Strengths & Dosage Forms

• Tablet: 150 mg, 300 mg
• Syrup: 75 mg / 5 ml
• Injection: 25 mg / ml

Purpose / Indications

It is used to reduce stomach acid and treat acid-related disorders.

Symptoms Ranitidine May Cure

• Acid reflux
• Heartburn
• Peptic ulcer
• GERD (Gastroesophageal reflux disease)
• Gastritis
• Zollinger-Ellison syndrome

Dosage

Adults

• GERD / Ulcer:
  150 mg twice daily
  Or
  300 mg once daily

Children

• Dose depends on body weight and physician prescription

⚠️ Dose should be adjusted as directed by a physician.

Mechanism of Action

Ranitidine blocks H2 receptors in gastric parietal cells

This leads to:

Reduced acid secretion
Reduced gastric volume
Reduced acidity

Result: Relief from ulcer and reflux symptoms

Detailed Explanation

Let’s first understand the role of histamines in stomach acid production, then we will be able to understand role of antihistamines in prevention of stomach acid production.

Role of histamine in stomach acid production

H2 receptors are present on the surface of gastric parietal cells in the stomach lining. These receptors regulate acid secretion. When histamine binds to H2 receptors, it activates parietal cells and stimulates the secretion of hydrochloric acid.

Role of Ranitidine in prevention of excessive stomach acid production

Ranitidine blocks these H2 receptors, preventing histamine from activating acid production. This reduces gastric acid secretion and helps treat conditions such as GERD, peptic ulcer, and acid reflux.

In one Line: H2 receptors are acid control switches on parietal cells, and Ranitidine blocks these switches to reduce acid production.

Additional pharmacological points

Bioavailability

Bioavailability refers to the percentage of a drug that reaches systemic circulation in an active form after administration.

Bioavailability of ranitidine is Approximately 50%

Half life

Half-life is the time required for the plasma concentration of a drug to reduce to half of its original value.

Half-life of ranitidine is 2–3 hours

Summary statement:

Ranitidine is an H₂ receptor blocker that reduces stomach acid production. In the stomach, histamine normally binds to H₂ receptors on parietal cells and stimulates acid secretion. Ranitidine blocks these H₂ receptors, preventing histamine from activating acid release. As a result, gastric acid secretion decreases, which helps treat conditions such as GERD, peptic ulcers, and acid reflux.

Side Effects

Common Side Effects

• Headache
• Dizziness
• Constipation
• Diarrhea

Less Common / Rare

• Confusion (elderly)
• Bradycardia
• Hypersensitivity

Contraindications

• Known hypersensitivity.
• Severe renal impairment (dose adjustment may be required)

Use in Special Populations

Pregnancy

• Generally considered safe (Category B– FDA older classification)
• Use only if clearly needed and prescribed by a physician

A drug is placed in Category B when animal reproductive studies have not shown a risk to the fetus, but there are no adequate and well-controlled studies in pregnant women. That means:

• Animal studies: Did not show evidence that the medicine causes fetal harm.
• Human data: Not enough good studies yet to confirm whether it’s absolutely safe or risky.

So Category B suggests the medicine may be safer than other categories, but this is not a guarantee—doctors still use it only if benefits outweigh potential risks.

Lactation

• Passes into breast milk
• Use cautiously

Elderly

• Usually safe
• Dose adjustment may be required in renal impairment

Drug Interactions

May interact with:

• Warfarin
• Ketoconazole
• Other acid-reducing drugs

Important Safety Note

Ranitidine has been withdrawn in many countries due to contamination with NDMA, a probable carcinogen.

Country / Region	Regulatory Authority	Year	Current Status
United States	FDA (Food and Drug Administration)	April 2020	❌ Withdrawn / banned
European Union	EMA (European Medicines Agency)	April 2020	❌ Suspended
United Kingdom	MHRA (Medicines and Healthcare products Regulatory Agency)	April 2020	❌ Suspended
Canada	Health Canada	April 2020	❌ Suspended
Australia	TGA (Therapeutic Goods Administration)	April 2020	❌ Banned
Germany	BfArM	2020	❌ Suspended
France	ANSM	2020	❌ Suspended
Italy	AIFA	2020	❌ Suspended
Spain	AEMPS	2020	❌ Suspended
India	CDSCO (Central Drugs Standard Control Organization)	2019	⚠️ Restricted / limited use
Japan	PMDA	2020	❌ Suspended
Switzerland	Swissmedic	2020	❌ Suspended

Cause	Details
Contaminant	NDMA (N-Nitrosodimethylamine)
Risk	Probable human carcinogen
Problem discovered	2018
Major withdrawal year	2020

Other safer alternatives include:

Famotidine
Omeprazole

Storage Instructions

• Store at room temperature
• Keep away from moisture and direct sunlight
• Keep out of reach of children

Disclaimer

This information is for educational purposes only and should not be used as a substitute for professional medical advice. Always consult a doctor or pharmacist before using any medication.

Key points / Revision

Point	Details
Drug Class	H2 blocker
Mechanism	Blocks H2 receptors
Use	GERD, ulcer
Acid secretion	Reduced
Duration	8–12 hours
Half-life	2–3 hours
Major concern	NDMA impurity
Alternative	Famotidine