Anticholinergics
Anticholinergics (e.g., atropine sulphate) reduce the rhythmic contractions and smooth muscle tone of the GI tract, thereby slowing peristalsis. They also have a drying effect and reduce gastric secretions.
Opiates
Opiate-related drugs, including loperamide and diphenoxylate hydrochloride with atropine, decrease bowel motility by acting on opiate receptors in the intestinal wall. This increases transit time, allowing for better absorption of water and electrolytes.
- Loperamide: The only opiate-related antidiarrheal available over-the-counter (OTC).
- Diphenoxylate with Atropine: A prescription-only combination; the atropine is included in subtherapeutic amounts to discourage recreational misuse.
Probiotics
Probiotics (e.g., Lactobacillus) are intestinal flora modifiers. They replenish the normal bacterial flora that may have been destroyed by antibiotics, helping to suppress the growth of diarrhea-causing bacteria.
⚠️ Clinical Warning: Patients with diarrhea caused by bacterial or parasitic infections must not use antidiarrheal drugs, as these medications can cause the organism to stay in the body longer, delaying recovery.
Laxatives
Laxatives are used to treat constipation through several different mechanisms.
Bulk-Forming Laxatives
These are considered the safest for long-term use and act similarly to dietary fiber. They absorb water into the intestine, increasing the bulk of the stool to distend the bowel and initiate reflex bowel activity.
- Examples: Methylcellulose (synthetic) and psyllium (natural).
- Patient Teaching: These must be taken with large amounts of water to prevent esophageal obstruction or fecal impaction.
Emollient Laxatives
Emollients are categorized into two types:
- Stool Softeners: Such as docusate sodium, which lower the surface tension of GI fluids to allow more water and fat to be absorbed into the stool.
- Lubricant Laxatives: Such as mineral oil, which lubricate the fecal material and the intestinal wall.
Hyperosmotic and Saline Laxatives
- Hyperosmotic Laxatives: Drugs like lactulose and polyethylene glycol (PEG) increase fecal water content through osmosis, resulting in distension and increased peristalsis.
- Saline Laxatives: Such as magnesium-based laxatives, increase osmotic pressure in the small intestine by inhibiting water absorption and increasing electrolyte secretion.
Stimulant Laxatives
Stimulant laxatives, including bisacodyl and senna, stimulate the nerves that innervate the intestines, directly increasing peristalsis.
- Caution: Long-term or inappropriate use of stimulant laxatives can lead to laxative dependency, a "lazy" or stretched colon, and nutrient malabsorption.
Clinical Monitoring and Patient Teaching
Fluid and Electrolyte Replacement
One of the most critical aspects of managing diarrhea is monitoring for fluid and electrolyte loss. Patients should be assessed for signs of dehydration, such as:
- Weakness or lethargy
- Decreased urinary output
- Dizziness
- Dry mucous membranes
Adverse Effects and Interactions
Pharmacological interventions carry specific risks:
- Anticholinergics: May cause urinary retention, blurred vision, and dry skin.
- Adsorbents: Can decrease the absorption of other drugs, such as digoxin or warfarin.
- Laxatives: Can cause electrolyte imbalances and, in the case of mineral oil, may decrease the absorption of fat-soluble vitamins (A, D, E, and K).
💡 Exam Tip: When teaching about bulk-forming laxatives like methylcellulose, always emphasize that the powder must be stirred into liquid and consumed immediately to prevent the product from congealing and causing esophageal obstruction.
Summary of Implementation
Effective bowel management involves a collaborative plan. For constipation, clinicians should encourage non-pharmacological interventions like increased fiber, fluid intake, and physical activity. For diarrhea, the priority is identifying the cause and ensuring the patient remains hydrated.
References
Antidiarrheal Drugs & Laxatives (Ch. 40).pdf
