What is the recommended management for an otherwise healthy adult presenting with mild to moderate watery diarrhea, including rehydration (oral rehydration solution), diet, anti‑motility therapy, and indications for intravenous fluids or antibiotics?

Management of Mild to Moderate Watery Diarrhea in Healthy Adults

For an otherwise healthy adult with mild to moderate watery diarrhea, reduced osmolarity oral rehydration solution (ORS) is the first-line treatment, empiric antibiotics should be avoided, and loperamide may be used cautiously only after adequate hydration in the absence of fever or bloody stools. 1

Rehydration Strategy

Oral Rehydration Solution (First-Line)

• Reduced osmolarity ORS (<250 mmol/L) is the cornerstone of treatment for mild to moderate dehydration 1
• Commercial formulations include Pedialyte, CeraLyte, or Enfalac Lytren 1, 2
• Adults should receive ad libitum ORS, up to approximately 2 liters per day 2
• Replace ongoing losses with ORS: 120-240 mL after each diarrheal stool 2
• Do not use apple juice, Gatorade, or soft drinks for rehydration—these have incorrect osmolarity and can worsen electrolyte imbalances 1, 2

When to Escalate to Intravenous Fluids

Isotonic IV fluids (lactated Ringer's or normal saline) are indicated when: 1

• Severe dehydration is present (≥10% fluid deficit with altered mental status, shock, poor perfusion)
• ORS therapy fails
• Patient has ileus
• Patient cannot tolerate oral intake despite attempts

Administer 20 mL/kg boluses rapidly and repeat until vital signs stabilize (pulse, perfusion, mental status normalize) 3

Dietary Management

• Resume age-appropriate usual diet during or immediately after rehydration is completed 1
• Do not withhold food or delay reintroduction—early feeding improves outcomes 1
• Diluted formulas or restrictive diets confer no benefit 1

Anti-Motility Therapy

Loperamide Use (With Strict Precautions)

• Loperamide may be given to immunocompetent adults with acute watery diarrhea ONLY after adequate hydration 1, 2
• Initial dose: 4 mg, followed by 2 mg every 2-4 hours or after each unformed stool 1
• Maximum daily dose: 16 mg 1

Absolute Contraindications to Loperamide

Do not give loperamide if: 1, 2

• Fever is present
• Bloody diarrhea (suggests inflammatory/invasive disease)
• Suspected toxic megacolon risk
• Any concern for STEC or inflammatory diarrhea

Antibiotic Therapy

When to Avoid Antibiotics (Most Cases)

• In most adults with acute watery diarrhea without recent international travel, empiric antimicrobial therapy is NOT recommended 1, 2
• Antibiotics increase resistance and may worsen STEC infections (risk of hemolytic uremic syndrome) 1, 2

Exceptions Where Antibiotics Should Be Considered

Consider empiric antibiotics only in: 1, 2

• Immunocompromised patients with severe illness
• Clinical features of sepsis with suspected enteric fever
• Bloody diarrhea with fever suggesting invasive bacterial infection

Avoid antibiotics entirely in suspected STEC O157 or Shiga toxin 2-producing E. coli 1, 2

Adjunctive Therapies

Antiemetics

• Ondansetron may be given to facilitate tolerance of oral rehydration in adults with significant vomiting 1, 2

Probiotics

• Probiotic preparations may be offered to reduce symptom severity and duration in immunocompetent adults 1

Common Pitfalls to Avoid

1. Do not withhold ORS in favor of IV fluids for mild-to-moderate dehydration—ORS is equally effective and avoids IV complications (phlebitis, infection risk) 1, 2

2. Do not give loperamide before ensuring adequate hydration—this can mask worsening dehydration and increase risk of complications 1, 2

3. Do not prescribe antibiotics empirically for simple watery diarrhea—this increases resistance without benefit in most cases 1, 2

4. Do not use sports drinks or juice for rehydration—incorrect osmolarity worsens electrolyte imbalances 1, 2

5. Monitor for signs of worsening dehydration during ORS administration—reassess frequently to ensure improvement 1