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PH6.3 | PH6.3 | Diarrhoea Pharmacotherapy — SDL Guide — SDL Guide (Part 3)
Management Plans — Acute and Chronic Diarrhoea
A management plan for diarrhoea must follow a logical decision sequence: classify the type → assess severity (dehydration grade) → identify the population (child vs adult, immunocompromised vs healthy) → match therapy to mechanism. The errors that cause harm almost always stem from skipping the classification step and going directly to 'give something to stop the diarrhoea.'
Management plan for acute watery diarrhoea (secretory, non-invasive):
Step 1: Assess dehydration — WHO grades: No dehydration (treat at home with ORS), Some dehydration (ORS 75 mL/kg over 4 hours, supervised), Severe dehydration (IV Ringer's lactate 100 mL/kg, then ORS when tolerating oral fluids).
Step 2: ORS — start immediately and continue until diarrhoea stops. Calculate ORS volumes by weight: 100 mL/kg for replacement + ongoing losses (10 mL/kg per stool). If the patient vomits, give smaller, more frequent sips.
Step 3: Zinc (children under 5) — 20 mg elemental zinc/day for 10–14 days, starting with rehydration.
Step 4: Anti-motility agent (adults, non-invasive) — loperamide may be added for non-bloody, non-febrile adult diarrhoea (travellers' diarrhoea, non-invasive acute gastroenteritis) to reduce stool frequency and allow normal activity.
Step 5: Continue feeding — do NOT withhold food or breast milk. Early refeeding prevents nutrition-related mucosal atrophy and accelerates mucosal recovery.
Management plan for acute invasive/dysenteric diarrhoea:
- ORS (always) + appropriate antibiotic (pathogen-matched or empirical ciprofloxacin/azithromycin)
- NO loperamide or anti-motility agents
- Stool culture if available (to guide antibiotic choice and detect resistant organisms)
- Notification to public health authority if Shigella or cholera (statutory notifiable disease in India)
Management plan for chronic diarrhoea:
- Full aetiological workup (colonoscopy, stool microbiology, coeliac serology, thyroid function, malabsorption tests)
- Treat the cause: IBD → 5-ASA/corticosteroids/biologics; IBS-D → loperamide + dietary modification (low-FODMAP); malabsorption → treat specific deficiency; Giardia → metronidazole
- Probiotics as adjunct in antibiotic-associated diarrhoea
| Clinical context | ORS | Zinc | Anti-motility | Antibiotic | Notes |
|---|---|---|---|---|---|
| Acute watery diarrhoea, child <5 | Yes | Yes | Avoid (racecadotril if needed) | No (viral) | WHO protocol |
| Acute watery diarrhoea, adult | Yes | No | Loperamide OK if non-invasive | No (unless Giardia/travellers') | — |
| Acute dysentery (bloody + fever) | Yes | — | CONTRAINDICATED | Yes (empirical) | Culture first if possible |
| C. difficile colitis | Yes | — | CONTRAINDICATED | Metronidazole/vancomycin | Stop precipitating antibiotic |
| IBS-D (chronic) | — | — | Loperamide (symptom control) | No | Diet modification first |
CLINICAL PEARL
The loperamide contraindication in invasive diarrhoea is a life-saving concept:
In 1996, a cluster of deaths occurred in Sub-Saharan Africa during a Shigella outbreak when loperamide was distributed as the antidiarrhoeal. By slowing intestinal motility, loperamide kept the invasive Shigella organisms in contact with the colonic mucosa for longer, worsening bacteraemia and systemic toxicity. In the context of E. coli O157:H7 (which produces Shiga toxin), anti-motility agents increase intestinal transit time, prolonging Shiga toxin contact with the gut epithelium and dramatically increasing the risk of haemolytic uraemic syndrome (HUS) — the leading cause of acute kidney injury in children in some regions.
The clinical rule is simple: blood in the stool + fever = stop, do not give loperamide. Assess for invasive diarrhoea first. In practice, if a patient presents with bloody diarrhoea and fever and asks for 'something to stop the diarrhoea,' the pharmacologically correct and potentially life-saving answer is to withhold the anti-motility agent, start ORS, and begin pathogen-targeted antibiotic therapy.
Self-Assessment — Diarrhoea Pharmacotherapy
The highest-yield clinical distinctions in diarrhoea pharmacotherapy are the ones that directly prevent patient harm. The self-assessment scenarios below test your ability to classify diarrhoea by mechanism and then select a therapy that is matched to that classification — or to recognise and reject a therapy that would cause harm. Two of the three questions involve identifying what NOT to give: prescribing restraint in the face of a request for inappropriate medication is a core clinical skill, particularly in a setting where loperamide is widely available over the counter and patients or parents often expect 'a tablet to stop the diarrhoea immediately.' Work through the pathophysiology for each scenario before looking at the options.
The highest-yield clinical distinctions in diarrhoea pharmacotherapy are the ones that directly prevent patient harm. The scenarios below test your ability to classify diarrhoea correctly and then select therapy that matches that classification. Two of the three questions involve recognising what NOT to give — a prescribing skill that is equally important as selecting the correct drug. For each scenario, work through the pathophysiology before looking at the options: what type of diarrhoea is this? What receptor or mechanism is appropriate? What is the contraindicated agent and why?
Work through the micro-quiz below before reviewing the explanations.
SELF-CHECK
A 60-year-old diabetic woman who completed a 10-day course of clindamycin for a skin infection 5 days ago now presents with profuse watery diarrhoea, abdominal cramping, and fever. Stool C. difficile toxin is positive. WBC is 18,000/mm³. What is the MOST appropriate antibiotic?
A. Oral metronidazole 400 mg three times daily for 10 days
B. Oral vancomycin 125 mg four times daily for 10 days
C. IV metronidazole 500 mg three times daily for 10 days
D. Restart clindamycin to restore normal gut flora
Reveal Answer
Answer: B. Oral vancomycin 125 mg four times daily for 10 days
This patient has severe C. difficile infection — high WBC (>15,000/mm³) is a marker of severity per IDSA guidelines. For severe C. difficile, oral vancomycin 125 mg four times daily × 10 days is the drug of choice. Metronidazole is inferior to vancomycin for severe disease (multiple RCTs demonstrate worse outcomes with metronidazole in severe CDI). Oral vancomycin works by remaining in the colon (it is not absorbed — negligible systemic bioavailability) and eliminating C. difficile directly from the intestinal lumen. IV metronidazole may be used as an adjunct when ileus prevents oral delivery, but oral vancomycin is the primary treatment for severe disease. Restarting clindamycin is the opposite of correct — stop all precipitating antibiotics and do not add more. Fidaxomicin is preferred for recurrent episodes.