Laxatives

Therapeutic Class: Gastrointestinal agents
Pharmacological Class: Laxatives / Cathartics
ATC Code: A06A
Regulatory Category: Mostly Over-the-Counter (OTC), some Prescription-Only (POM)
Available Forms: Oral tablets, capsules, powders, granules, syrups, liquids, enemas, suppositories

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Definition and Classification

Laxatives are a class of agents that promote defecation, either by increasing the bulk and moisture of stools, stimulating peristalsis, lubricating the intestinal tract, or softening the stool consistency. They are primarily indicated for short-term management of constipation, preparation for diagnostic procedures, and, in some cases, chronic bowel regulation under medical supervision.

Laxatives are pharmacologically classified into the following major categories:

1. Bulk-forming laxatives

2. Osmotic laxatives

3. Stimulant (contact) laxatives

4. Stool softeners (emollient laxatives)

5. Lubricant laxatives

6. Enemas and suppositories

7. Chloride channel activators and secretagogues (for chronic constipation, prescription-only)

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1. Bulk-Forming Laxatives

Examples:

• Psyllium (Metamucil)

• Methylcellulose (Citrucel)

• Sterculia

• Calcium polycarbophil

Mechanism:

Absorb water in the intestine to form a viscous compound, which increases stool bulk and triggers peristalsis.

Onset:

12–72 hours

Clinical Use:

• First-line for chronic constipation

• Safe in long-term use

• Useful in IBS with constipation

Cautions:

• Must be taken with adequate fluids to prevent intestinal obstruction

• Not suitable for patients with dysphagia or significant narrowing of the GI tract

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2. Osmotic Laxatives

Subtypes and Examples:

• Saline osmotics:

  • Magnesium hydroxide

  • Magnesium sulfate

  • Sodium phosphate

• Non-saline osmotics:

  • Lactulose

  • Sorbitol

  • Polyethylene glycol (PEG/macrogol)

  • Glycerol suppositories

Mechanism:

Draw water into the colon via osmosis, increasing water content of the stool and promoting bowel movement.

Onset:

• PEG: 24–72 hours

• Lactulose: 24–48 hours

• Saline types: 0.5–3 hours

Clinical Use:

• Short-term relief of occasional constipation

• Bowel cleansing before surgery or colonoscopy (PEG, sodium phosphate)

Cautions:

• Risk of electrolyte imbalance in elderly and renal impairment

• Avoid phosphate enemas in frail or renally impaired individuals

• Lactulose can cause flatulence and bloating

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3. Stimulant (Contact) Laxatives

Examples:

• Senna

• Bisacodyl

• Sodium picosulfate

• Cascara

• Castor oil (rarely used today)

Mechanism:

Stimulate the enteric nerves to induce peristalsis and increase secretion of fluids and electrolytes in the colon.

Onset:

• Oral: 6–12 hours

• Rectal: 15–60 minutes

Clinical Use:

• Short-term constipation

• Bowel prep (e.g., bisacodyl with PEG)

Cautions:

• Risk of cramping and electrolyte imbalance

• Avoid long-term use due to possible cathartic colon, dependence, and melanosis coli

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4. Stool Softeners (Emollient Laxatives)

Examples:

• Docusate sodium (Colace)

• Docusate calcium

• Liquid paraffin (mineral oil)

Mechanism:

Reduce surface tension of the stool, allowing water and fats to penetrate and soften fecal mass.

Onset:

12–72 hours (oral), 2–15 minutes (rectal)

Clinical Use:

• Patients who should avoid straining (e.g., post-MI, anal fissures, hemorrhoids)

• Adjunct in opioid-induced constipation

Cautions:

• Not very effective as monotherapy

• Risk of lipoid pneumonia with aspiration of mineral oil

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5. Lubricant Laxatives

Examples:

• Mineral oil (liquid paraffin)

Mechanism:

Coat the stool and intestinal mucosa to reduce water absorption and ease passage.

Onset:

6–8 hours (oral), ~15 minutes (rectal)

Cautions:

• Decreases absorption of fat-soluble vitamins (A, D, E, K)

• Not recommended for chronic use

• Risk of aspiration in bedridden patients

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6. Rectal Agents: Enemas and Suppositories

Examples:

• Glycerin suppository

• Bisacodyl suppository

• Sodium phosphate enema

• Microlax (sodium citrate enema)

• Soap suds enema

Mechanism:

Direct stimulation or osmotic effect in the rectum, promoting defecation reflex.

Onset:

• Suppositories: 15–60 minutes

• Enemas: 5–15 minutes

Use:

• Rapid relief of acute constipation

• Commonly used in pediatric patients

• Hospital use for rectal clearance

Cautions:

• Electrolyte disturbances with repeated phosphate enemas

• Avoid frequent use to prevent dependency and mucosal damage

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7. Prescription Agents for Chronic Idiopathic Constipation

Examples:

• Lubiprostone: Chloride channel activator

• Linaclotide: Guanylate cyclase-C agonist

• Plecanatide

• Prucalopride: 5-HT4 agonist (prokinetic)

Mechanism:

Enhance intestinal secretion and motility through specific receptor activation.

Indication:

• Chronic idiopathic constipation (CIC)

• Irritable bowel syndrome with constipation (IBS-C)

Use:

• For patients unresponsive to conventional laxatives

• Prescription-only, usually reserved for specialist recommendation

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General Clinical Indications

• Acute constipation

• Opioid-induced constipation (often requires stimulant + stool softener)

• Preparation for colonoscopy or surgery

• Chronic idiopathic constipation (with monitoring)

• Preventing straining in cardiovascular, neurological, or anorectal conditions

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Contraindications (General)

• Bowel obstruction or perforation

• Inflammatory bowel diseases (active phase)

• Severe dehydration or electrolyte imbalance

• Undiagnosed abdominal pain

• Rectal bleeding of unknown origin

• Hypersensitivity to ingredients

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Adverse Effects (Class-Specific)

Class	Adverse Effects
Bulk-forming	Bloating, flatulence, esophageal obstruction (if dry)
Osmotic	Diarrhea, electrolyte loss (especially Mg or Na)
Stimulant	Abdominal cramps, dependency, melanosis coli
Stool softeners	Minimal; rare diarrhea or throat irritation (liquid)
Lubricants	Aspiration pneumonia, malabsorption
Enemas/suppositories	Mucosal irritation, phosphate overload
Secretagogues	Diarrhea, nausea, flatulence

Drug Interactions

• Mineral oil reduces absorption of fat-soluble vitamins

• Sodium phosphate enemas may cause hyperphosphatemia in those on ACE inhibitors, diuretics, or NSAIDs

• Bulk-forming agents may reduce absorption of oral medications – separate by at least 2 hours

• Lactulose and antacids: may neutralize acidic pH needed for lactulose fermentation

• Polyethylene glycol (PEG) may affect absorption of poorly soluble drugs like digoxin

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Use in Special Populations

Children:

• Glycerin suppositories, lactulose, and PEG are preferred

• Avoid stimulant and phosphate enemas unless advised by a physician

Pregnancy:

• Bulk-forming agents and lactulose are considered safe

• Avoid stimulant and lubricant laxatives unless clinically necessary

Elderly:

• Prefer osmotic or bulk agents

• Watch for dehydration, electrolyte imbalances

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Monitoring Parameters

• Frequency and consistency of bowel movements

• Electrolyte levels with prolonged use

• Signs of dependence (frequent use of stimulants)

• Hydration status

• Underlying causes of constipation (diet, inactivity, medications)

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Patient Counseling Points

• Maintain adequate hydration (1.5–2.5 L/day)

• Increase dietary fiber intake gradually to avoid bloating

• Establish a regular bowel routine

• Avoid overuse of stimulant laxatives

• Report signs of rectal bleeding, persistent constipation, or abdominal pain

• For bulk-forming agents: Take with a full glass of water

• For rectal agents: Only for short-term, emergency use

• Review any medications causing constipation (opioids, anticholinergics, calcium supplements, etc.)