Drugs Acting on the Gastrointestinal System

Alumkal

Introduction

  • The gastrointestinal (GIT) system plays a vital role in digestion, absorption of nutrients, and elimination of waste products.

  • Various disorders such as vomiting, diarrhoea, constipation, hyperacidity, and intestinal infections can disturb normal GIT function.

  • Drugs acting on the GIT system are used to control symptoms, correct physiological disturbances, and treat underlying causes of digestive disorders.

  • These drugs may either stimulate or inhibit gastrointestinal motility, secretion, or absorption.

  • Important groups include emetics, anti-emetics, anti-diarrhoeal drugs, laxatives, purgatives, antacids, and drugs affecting gastric secretion.

  • Among them, emetics, anti-diarrhoeal agents, and laxatives are commonly used in clinical practice.

  • These drugs act through different mechanisms such as stimulation of vomiting centre, inhibition of intestinal motility, or facilitation of bowel movement.

  • Understanding their mechanism of action, therapeutic uses, side effects, and adverse effects is essential for safe clinical use.

 

Emetics

Emetics are drugs that induce vomiting by stimulating the vomiting center or chemoreceptor trigger zone (CTZ) in the brain.

Mechanism of Action

  • Emetics act mainly by two mechanisms:

    • Central action: Stimulate the chemoreceptor trigger zone in the medulla.

    • Peripheral action: Irritate the gastric mucosa, which sends signals to the vomiting center.

Examples of Emetics

Drug Mechanism Notes
Apomorphine Stimulates CTZ in brain Acts rapidly
Ipecac syrup Gastric irritation + CTZ stimulation Traditionally used in poisoning
Copper sulfate Irritates stomach mucosa Rarely used

Therapeutic Uses

  • Used in acute poisoning to remove toxic substances from the stomach.

  • Used when gastric lavage is not immediately available.

  • Used in overdose of certain drugs when vomiting can remove the toxin.

  • Previously used in household poisoning emergencies.

Side Effects

  • Nausea

  • Excessive vomiting

  • Abdominal cramps

  • Gastric irritation

Adverse Effects

  • Aspiration pneumonia

  • Electrolyte imbalance

  • Severe dehydration

  • Damage to gastric mucosa

 

Anti-Diarrhoeal Drugs

Anti-diarrhoeal drugs are medications that reduce intestinal motility, secretion, or infection, thereby controlling diarrhoea.

Causes of Diarrhoea

  • Bacterial infections

  • Viral infections

  • Food poisoning

  • Irritable bowel syndrome

  • Inflammatory bowel disease

Classification of Anti-Diarrhoeal Drugs

Class Examples Mechanism
Opioid derivatives Loperamide, Diphenoxylate Reduce intestinal motility
Adsorbents Kaolin, Pectin Adsorb toxins and microorganisms
Anticholinergic drugs Atropine Reduce intestinal spasms
Antimicrobial drugs Metronidazole, Ciprofloxacin Kill infectious organisms
Probiotics Lactobacillus Restore intestinal flora

Mechanism of Action

  • Decrease intestinal motility allowing more water absorption.

  • Reduce intestinal secretion.

  • Adsorb toxins produced by bacteria.

  • Eliminate infectious microorganisms.

Therapeutic Uses

  • Acute diarrhoea

  • Traveller’s diarrhoea

  • Chronic diarrhoea

  • Irritable bowel syndrome

  • Infective diarrhoea (with antimicrobials)

Side Effects

  • Constipation

  • Abdominal discomfort

  • Drowsiness

  • Dry mouth

Adverse Effects

  • Paralytic ileus

  • Toxic megacolon (rare)

  • Severe dehydration if untreated infection persists

  • Drug dependency (with opioid derivatives)

 

Laxatives and Purgatives

  • Laxatives are drugs that promote bowel movement and relieve constipation.

  • Purgatives are stronger agents that cause complete evacuation of the bowel.

Classification of Laxatives

Type Examples Mechanism
Bulk forming laxatives Psyllium, Bran, Methylcellulose Increase stool bulk
Osmotic laxatives Lactulose, Magnesium sulfate Draw water into intestine
Stimulant laxatives Senna, Bisacodyl, Castor oil Stimulate intestinal motility
Stool softeners Docusate sodium Soften stool by increasing water penetration
Lubricant laxatives Liquid paraffin Lubricate intestinal contents

Mechanism of Action

  • Bulk forming agents: Increase fecal mass and stimulate peristalsis.

  • Osmotic agents: Retain water in intestine, softening stool.

  • Stimulant laxatives: Directly stimulate intestinal muscles.

  • Stool softeners: Reduce surface tension allowing water entry into stool.

  • Lubricants: Coat intestinal wall and stool to ease passage.

Therapeutic Uses

  • Treatment of constipation

  • Preparation of bowel before surgery or colonoscopy

  • Prevention of straining in hemorrhoids, hernia, and cardiovascular diseases

  • Used in hepatic encephalopathy (lactulose) to reduce ammonia levels

Side Effects

  • Abdominal cramps

  • Diarrhoea

  • Nausea

  • Flatulence

Adverse Effects

  • Electrolyte imbalance

  • Dehydration

  • Intestinal obstruction (rare)

  • Dependency with prolonged use

  • Malabsorption of fat-soluble vitamins (with liquid paraffin)

 

Comparison of Major GIT Drug Groups

Drug Group Main Function Examples Major Use
Emetics Induce vomiting Apomorphine, Ipecac Poison removal
Anti-diarrhoeal drugs Reduce diarrhoea Loperamide, Diphenoxylate Acute diarrhoea
Laxatives Relieve constipation Senna, Lactulose Constipation treatment

 

General Precautions in GIT Drug Therapy

  • Use emetics only under medical supervision.

  • Avoid anti-diarrhoeal drugs in severe bacterial infection with high fever.

  • Maintain adequate hydration during diarrhoea.

  • Avoid chronic use of stimulant laxatives to prevent dependency.

  • Consider underlying cause of GIT disorder before drug therapy.

  • Monitor electrolyte balance and hydration status.