Antidiarrhoeals and Laxatives: Classification


  • What are they?

Diarrhea can be explained as a frequent, often precipitate passage of poorly formed stools. The WHO defines the condition as 3 or more loose or watery stools in a period of 24-hours. Pathologically, it can be explained as a condition where the excess passage of water occurs in the feces. Diarrhea can be a cause of

  • Decreased electrolyte and water absorption
    • Increased secretion by the intestinal mucosa
    • Increased luminal osmotic load
    • Inflammation of mucosa and exudation into the lumen.

The drugs used for such conditions are known as antidiarrheal drugs.

  • How do they work?

Rational management for diarrhea treatment depends on investigating the underlying cause and prescribing drugs for specific therapy (if necessary). Since most diarrheas are self-limiting, it is not advisable to take self-medication until necessary.

The majority of diarrhea-causing entero-pathogens are prevented from causing infection, by motility and other protective gut mechanisms. Drugs for therapeutic management can be broadly grouped into:                                            

(a) Treatment of fluid depletion, shock, and acidosis – rehydration is majorly required that can be done orally or I.V. depending on the severity.

(b) Maintenance of nutrition   – the patients of diarrhea should not be starved or given lesser food. This is because fasting decreases the brush-border enzymes that reduce salt, water, and nutrient absorption, leading to malnutrition. Simple food like half-strength buffalo milk, boiled potato, rice, chicken soup, banana should be given as soon as the patient can eat.

(c) Drug therapy – these are the drugs used to calm irritated bowel for symptomatic relief.

The severity and nature of diarrhea govern the relative importance of each measure.

  • Different classes of these drugs

Rehydrating agents

  1. Intravenous rehydration – needed in severe fluid loss (>10% of body weight). Recommended I.V. fluid composition – 5g NaCl, 1g KCl, 4g NaHCO3 in 1L water, or 5% glucose solution. (Dhaka fluid). The volume equal to 10% body weight is infused over 2-4 hours.
  2. Oral rehydration therapy (ORT) – ORT is the widely used treatment in the cases of mild (5-7% of body weight) to moderate (7.5-10% of body weight) fluid loss from the very beginning. Patients are advised to drink ORS as 30-60 minutes interval.

Drug therapy

  1. Bulking agents (absorbents)– these agents are used for diarrhea in functional bowel disease.

Drugs – guar gum or plant fibers (bran, sterculia, isabgol)

  • Absorbents – absorb toxic substances that cause infective diarrhea  

Drug – Methylcellulose, carboxymethyl cellulose, kaolin, pectin, attapulgite

  • Anti-inflammatory – Locally coat the lining of the GIT to soothe the irritation that may stimulate the reflex

Drugs – bismuth subsalicylate (anti-inflammatory – subsalicylate, anti-bacterial – bismuth)

  • Anticholinergics – reduce intestinal movement and are effective against both diarrhea and accompanying cramping

Drugs – metoclopramide, neostigmine, atropine

  • Opioids – Opioids have agonist actions on the intestinal opioid receptors, which when activated cause constipation

Drugs – loperamide, opium tincture, difenoxin, diphenoxylate

  • Probiotics – used as dietary supplementation for bacterial replacement

Drug- Lactobacillus acidophilus

  • Indications in which they are used
  • Acute (2-3 weeks) and chronic diarrhea (>3 weeks)
  • Reduction of fecal discharges from ileostomies
  • Management and treatment of Traveler’s diarrhea
  • Poisoning
  • Drug allergy
  • GI obstruction
  • Acute abdominal conditions
  • Ulcerative colitis
  • Side effects
  • Constipation
  • Nausea, vomiting
  • Abdominal distention and discomfort
  • Toxic megacolon
  • Contraindications
  • Loperamide contraindicated in children below 4 years of age
  • Loperamide contraindicated in infective diarrhea, ulcerative colitis, irritable bowel syndrome
  • All drugs are contraindicated in bloody diarrhea, fever, or systemic toxicity
  • Discontinue the therapy if the condition does not improve
  • Bile tract disease
  • Crohn’s disease


  • What are they?

Known by several different names – aperients, purgatives, cathartics; these drugs are used for management and treatment of conditions associated with GIT, wherein the normal motility is greatly reduced. Laxatives aid the patients with fecal retention problems directly by increasing the bulk and smoothening the bowel movement.

Upon long term use, they interfere with the natural bowel movement, causing discomfort.

The distinction of drugs is sometimes made on the intensity of action, as many drugs in low doses act as laxatives and as purgatives at larger doses.

  • How do they work?

The laxative drugs primarily aid in increasing the water content in the feces. The action can be achieved by several different mechanisms that form the basis of different types of drugs used for laxative action. The effect is generally achieved by one or more than one of the following mechanisms

  • An osmotic action that causes water and electrolytes accumulation, in intestinal lumen. This increases the volume of fecal content and makes it easier to excrete.
  • Action on mucosa epithelia, decreasing the overall absorption of water and electrolytes. The intestinal transit is enhanced indirectly by the liquid bulk.
  • Cause an increase in the propulsive activity as a primary action that allows less time for absorption of water and salt as a secondary effect.

Laxatives thus modify the fluid dynamic and mucosal epithelia causing fluid accumulation in the lumen by regulating intracellular responses and physiological processes

  • Different classes of drugs

Bulk-forming laxatives – the laxatives under this class are high-fiber content compounds that absorb water to increase the bulk, hence the name. The formed bulk then distends the bowel movement to initiate reflex bowel activity. These compounds also help in softening the stool for easy passage.

Drugs – psyllium husk, methylcellulose, polycarbophil, bran

Emollient – these laxatives are stool softeners and lubricants. These soften stool by water accumulation in the lumen by action on bolus and increase the penetration of water into the feces. Other than water, they also promote fat into the stools, lubricating both fecal material and intestinal walls.

Drugs – docusate salts (DOSS), liquid paraffin

Hyperosmotic – these are solutes going unabsorbed in the intestine, have a property to retain water osmotically, and distend the bowel; increasing the peristalsis indirectly

Drugs – polyethylene glycol, sorbitol, glycerin, lactulose

Saline – saline laxatives increase the osmotic pressure within the intestinal tract, which results in a higher amount of water to move into the intestinal lumen. The action results in bowel distention, increased peristalsis, and evacuation

Drugs – magnesium sulfate, magnesium hydroxide, magnesium citrate, sodium phosphate

Stimulant – as the name suggests, these agents stimulate the intestinal nervous network. The action on myenteric plexes increases the peristalsis and motility. More importantly, they aid in intestinal water and electrolyte accumulation by modulating the absorptive and secretory activity of mucosal epithelia.

Drugs – castor oil, senna, cascara, bisacodyl

  • Indications in which they are preferred
  • Adjunct in anti-helminthic therapy
  • Chronic and acute constipation
  • Hepatocellular failure
  • Preparation and cleaning bowel before radiography of GIT, proctoscopy or colonoscopy
  • For rapid removal of poisonous substance in the GI tract
  • As a post-operative medication to avoid strain
  • In bedridden patients
  • To avoid strain in patients with a hernia, hemorrhoids, and cardiovascular disease
  • Side effects

Common side effects of all laxatives –

  • Diarrhea
  • Abdominal cramping
  • Nausea
  • Fluid and electrolyte imbalance
  • Sympathetic reactions – sweating, palpitations, flushing, and fainting
  • Cathartic dependence

Specific side effects –

  • Bulk Forming Laxatives – Impaction and fluid overload
  • Emollient Laxatives –  Skin rashes and decreased vitamin
  • Hyperosmotic Laxatives – Abdominal bloating and rectal irritations
  • Saline Laxatives –  Magnesium toxicity (renal insufficient patients), cramping, diarrhea, increased thirst
  • Stimulant Laxatives – Nutrient malabsorption, skin rashes, gastric irritation, rectal irritation
  • Contraindications
    • Appendicitis, diverticulitis, ulcerative colitis
    • Absence of peristalsis
  • A sudden, unexpected change in bowel movement
  • Oesophageal obstruction
  • Intestinal obstruction
  • Fecal impaction
  • Undiagnosed abdominal pain
  • Colic pain and vomiting
  • Drug-induced secondary constipation
  • Secondary constipation due to – hypothyroidism, hypercalcemia, malignancies, stricture

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