What is the recommended assessment and management of acute diarrhea, including severity assessment, oral rehydration therapy, antidiarrheal and antibiotic use, and red‑flag criteria, especially in children, elderly, pregnant or immunocompromised patients?

Management of Acute Diarrhea

Immediate Assessment of Dehydration Severity

Classify dehydration immediately using clinical signs: mild (3-5% fluid deficit), moderate (6-9% deficit), or severe (≥10% deficit with shock), as this single determination drives all subsequent management decisions. 1

• Capillary refill time is the most reliable predictor of dehydration in children, superior to sunken fontanelle or absent tears 1
• Examine skin turgor (pinch test showing tenting), mucous membranes (dry vs moist), mental status (lethargy, irritability), pulse quality, and breathing pattern (rapid/deep suggests acidosis) 2, 1
• Obtain body weight immediately to calculate precise fluid deficit 1
• Severe dehydration signs: severe lethargy or altered consciousness, prolonged skin tenting >2 seconds, cool poorly perfused extremities, delayed capillary refill, rapid deep breathing 1

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Rehydration Protocol by Severity

Severe Dehydration (≥10% deficit) – MEDICAL EMERGENCY

Administer 20 mL/kg boluses of Ringer's lactate or normal saline IV immediately, repeating boluses until pulse, perfusion, and mental status normalize. 1

• Do not delay IV access; this is life-saving 1
• Once circulation restored, transition to oral rehydration solution (ORS) for remaining deficit 1
• Monitor continuously for improvement in vital signs and perfusion 1

Moderate Dehydration (6-9% deficit)

Administer 100 mL/kg of ORS containing 50-90 mEq/L sodium over 2-4 hours. 1

• Start with very small volumes (one teaspoon) using spoon, syringe, or medicine dropper, gradually escalating as tolerated 1
• Consider nasogastric administration if oral intake not tolerated 1

Mild Dehydration (3-5% deficit)

Administer 50 mL/kg of ORS over 2-4 hours using the same small-volume, frequent administration technique. 1

No Dehydration

Skip rehydration phase entirely and proceed directly to maintenance therapy with ongoing loss replacement. 2

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Managing Concurrent Vomiting

Give 5 mL of ORS every 1-2 minutes using a spoon or syringe; vomiting often decreases as dehydration corrects. 2, 1

• Gradual, supervised administration prevents triggering more vomiting 3
• For persistent vomiting despite this technique, consider continuous slow nasogastric infusion 3
• Ondansetron may reduce vomiting in children >4 years but is contraindicated in infants <4 years 3

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Replacing Ongoing Losses

Administer 10 mL/kg of ORS for each watery/loose stool and 2 mL/kg for each vomiting episode throughout the illness. 2, 1

• Measure or estimate stool losses; if measured accurately, give 1 mL ORS per gram of diarrheal stool 2
• Continue replacement until diarrhea and vomiting resolve 3

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Reassessment and Monitoring

Reassess hydration status after 2-4 hours of rehydration therapy. 1

• If rehydrated, transition to maintenance phase with ongoing loss replacement 1
• If still dehydrated, recalculate fluid deficit and restart rehydration protocol 3
• Hydration status should be assessed frequently during therapy 2

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Nutritional Management

Infants

Continue breastfeeding on demand without any interruption throughout the entire diarrheal episode. 2, 1, 3

For formula-fed infants, resume full-strength, lactose-free or lactose-reduced formula immediately upon rehydration. 2, 1, 3

• When lactose-free formulas unavailable, use full-strength lactose-containing formula under supervision 2, 3
• True lactose intolerance is indicated by severe worsening diarrhea upon reintroduction, not just low stool pH (<6.0) or reducing substances (>0.5%) 2, 1
• If lactose intolerance confirmed, temporarily reduce or remove lactose from diet 2

Older Children

Resume age-appropriate diet immediately upon rehydration: starches, cereals, yogurt, fruits, and vegetables. 2, 1

• Avoid foods high in simple sugars and fats during acute phase as they exacerbate stool output 2, 1
• Do not impose "bowel rest"—there is no justification for withholding food 1

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Zinc Supplementation

Administer oral zinc supplementation in children 6 months to 5 years, particularly those with signs of malnutrition, as it reduces diarrhea duration. 3

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Antibiotic Therapy – Rarely Indicated

Antibiotics are NOT routinely indicated for acute watery diarrhea. 2, 1, 3

Consider antibiotics only when:

• Dysentery (bloody diarrhea) with high fever is present 2, 1
• Watery diarrhea persists >5 days 2, 1
• Stool cultures indicate specific pathogen requiring treatment 2, 1

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Antidiarrheal Agents – CONTRAINDICATED in Children

Loperamide and all antimotility drugs are ABSOLUTELY CONTRAINDICATED in all children <18 years due to risks of respiratory depression and serious cardiac adverse reactions. 1, 4

• This is an FDA black-box level contraindication 4
• Even in adults, avoid dosages >16 mg/day due to cardiac risks 4

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Red-Flag Criteria Requiring Immediate Medical Evaluation

Instruct caregivers to return immediately if any of the following develop: 1, 3

• Persistent watery stools continuing or worsening
• High fever
• Bloody diarrhea
• Intractable vomiting preventing fluid intake
• Decreased urine output (fewer than 3 wet diapers in 24 hours)
• Sunken eyes or increased thirst
• Severe lethargy, irritability, or worsening mental status
• High stool output (>10 mL/kg/hour)

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Special Populations

Elderly Patients

• More susceptible to QT prolongation effects; avoid loperamide in elderly taking Class IA or III antiarrhythmics 4
• No dose adjustment of loperamide required for renal impairment, but use caution in hepatic impairment due to increased systemic exposure 4

Immunocompromised Patients

• Higher risk of complications and severe dehydration 5
• Lower threshold for antibiotic therapy 2
• More aggressive monitoring required 5

Pregnant Patients

• Prioritize oral rehydration to avoid IV access risks when possible 6
• Avoid antimotility agents 7

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Fluid Selection: What NOT to Use

Do NOT use cola, apple juice, sports drinks, or other "clear liquids" for rehydration—they contain inadequate sodium and excessive sugar, causing osmotic diarrhea and electrolyte imbalance. 3

• Use commercially prepared ORS (e.g., Pedialyte with ~45-90 mEq/L sodium) 1, 3
• Homemade salt-sugar solutions lack proper electrolyte composition 1

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Home Management and Prevention

Parents should keep ORS sachets at home and begin administration at the first sign of diarrhea. 3

• Provide detailed written and oral instructions on mixing ORS from powder formulations 3
• Educate parents at first newborn visit and reinforce at well-baby examinations 2
• Hand hygiene after diaper changes, before food preparation, and before eating prevents transmission 3

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Common Pitfalls to Avoid

• Do not withhold food—"bowel rest" delays nutritional recovery and has no evidence base 1
• Do not rely solely on sunken fontanelle or absent tears for dehydration assessment; use capillary refill and skin turgor 1
• Do not routinely order laboratory tests for mild-moderate dehydration without specific clinical indications 1
• Do not use stimulant laxatives (this is for constipation, not diarrhea) 8
• Do not assume antibiotics are needed—most acute diarrhea is viral and self-limited 2, 3