What is the recommended management for an otherwise healthy adult with mild‑to‑moderate acute watery diarrhea lasting less than 14 days?

Management of Acute Watery Diarrhea in Healthy Adults

Begin immediate oral rehydration with reduced-osmolarity ORS and avoid empiric antibiotics—rehydration prevents morbidity and mortality, while antibiotics offer no benefit in uncomplicated cases. 1, 2

Immediate Rehydration: The Cornerstone of Treatment

Reduced-osmolarity oral rehydration solution (65–70 mEq/L sodium, 75–90 mmol/L glucose) is first-line therapy for all adults with acute watery diarrhea, regardless of severity. 1, 2

• Prescribe 2.2–4.0 liters of total fluid intake per day, matching ongoing losses from urine (approximately 1 L/day), insensible losses (30–50 mL/hour), and stool output. 2
• For mild dehydration (3–5% fluid deficit with slight thirst and mildly dry mucous membranes): administer 50 mL/kg ORS over 2–4 hours. 2
• For moderate dehydration (6–9% deficit with loss of skin turgor and dry mucous membranes): administer 100 mL/kg ORS over 2–4 hours. 2, 3
• Continue ORS until clinical signs of dehydration resolve and diarrhea stops. 1, 2
• If commercial ORS is unavailable, diluted fruit juices with saltine crackers and broths can meet fluid and salt needs for mild illness, though ORS is superior. 2

When to Escalate to Intravenous Fluids

Switch immediately to isotonic IV fluids (lactated Ringer's or normal saline) if any of the following develop: 1, 2, 3

• Severe dehydration (≥10% fluid deficit) with prolonged skin tenting >2 seconds, cool/poorly perfused extremities, or decreased capillary refill
• Altered mental status or inability to tolerate oral intake
• Shock (hypotension, tachycardia unresponsive to oral fluids)
• Failure of oral rehydration therapy or presence of ileus

Administer IV fluids at 60–100 mL/kg over the first 2–4 hours until pulse, perfusion, and mental status normalize, then transition to ORS for remaining deficit replacement. 2, 3, 4

Antibiotic Stewardship: When NOT to Prescribe

Do not prescribe empiric antibiotics for uncomplicated acute watery diarrhea in stable, immunocompetent adults without recent international travel. 1, 2, 3

• Antibiotics do not shorten illness duration in viral or non-invasive bacterial diarrhea and promote antimicrobial resistance. 1, 2
• Absence of fever indicates low probability of invasive bacterial pathogens (Shigella, Campylobacter, Salmonella). 2
• Lack of blood or leukocytes in stool excludes dysentery and inflammatory diarrhea, the only scenarios where antibiotics demonstrate benefit. 2

Exceptions: When Antibiotics ARE Indicated

Reserve antibiotics for: 1, 2, 5

• Fever with bloody diarrhea (suggesting invasive pathogens)
• Recent international travel with severe, incapacitating symptoms (travelers' diarrhea)
• Immunocompromised patients or ill-appearing infants
• Suspected enteric fever with sepsis features

Preferred regimen: Azithromycin 500 mg single dose for watery diarrhea or 1,000 mg single dose for dysentery. 2, 5 Fluoroquinolones (ciprofloxacin 750 mg or levofloxacin 500 mg single dose) are alternatives but face rising resistance, particularly in Campylobacter. 2, 5

Symptomatic Management with Loperamide

After adequate rehydration, loperamide may be used in immunocompetent adults with watery diarrhea to reduce stool frequency and improve quality of life. 1, 2, 6

• Dosing: 4 mg initially, then 2 mg after each loose stool, maximum 16 mg daily. 2, 6
• Never use loperamide if fever or bloody stools are present—this suggests inflammatory diarrhea where antimotility agents risk toxic megacolon and prolonged infection. 1, 2, 3, 6
• Never use loperamide in children <18 years. 1, 3, 6
• Avoid in elderly patients taking QT-prolonging drugs (Class IA or III antiarrhythmics) due to cardiac risk. 6
• Caution with concomitant CYP3A4 inhibitors (itraconazole), CYP2C8 inhibitors (gemfibrozil), or P-glycoprotein inhibitors (quinidine, ritonavir), as these increase loperamide exposure and cardiac adverse reaction risk. 6

Dietary Management

Resume a normal, age-appropriate diet immediately after rehydration is complete. 1, 2, 3

• Early feeding improves outcomes; do not restrict diet during or after rehydration. 3
• Initially favor small, light meals and avoid heavy, fatty, spicy foods and caffeine for comfort. 2

Adjunctive Therapies

• Antiemetic agents (ondansetron) may be considered after adequate rehydration to facilitate ORS tolerance, but they do not replace fluid therapy. 1, 3
• Probiotics may be offered to reduce symptom severity and duration, though evidence is mixed and benefits appear modest. 2, 3, 7

Critical Pitfalls to Avoid

• Never prioritize antimotility agents over rehydration—dehydration, not diarrhea itself, drives morbidity and mortality in diarrheal illness. 2, 3
• Never use antibiotics routinely—they promote resistance without benefit in uncomplicated watery diarrhea. 1, 2, 3
• Never use loperamide when fever or bloody stools develop—this risks toxic megacolon. 1, 2, 3, 6
• Never treat asymptomatic contacts with empiric or preventive antibiotics; advise hand hygiene and infection control measures instead. 1, 3
• Avoid overhydration in elderly patients with heart or kidney failure—frequent reassessment is essential. 2

When to Reassess or Escalate Care

• If no clinical improvement occurs within 48 hours, discontinue loperamide and contact a healthcare provider. 6, 8
• Obtain stool cultures or microbiologic studies only if symptoms persist >14 days, fever develops, bloody stools appear, or empiric therapy fails. 2
• Seek immediate care for fainting, rapid or irregular heartbeat, or unresponsiveness. 6