What should I prescribe for an adult with acute gastroenteritis presenting with non‑bloody diarrhea and no contraindications?

Management of Acute Gastroenteritis in Adults with Non-Bloody Diarrhea

For an adult with acute gastroenteritis presenting with non-bloody diarrhea and no contraindications, prescribe oral rehydration solution (ORS) as first-line therapy, and consider loperamide only after adequate hydration is achieved if the patient is immunocompetent and has no fever. 1

Primary Treatment: Oral Rehydration

Reduced osmolarity ORS is the cornerstone of therapy for mild to moderate dehydration and should be initiated immediately. 1 This recommendation comes from the 2017 Infectious Diseases Society of America guidelines, which provide the most authoritative guidance on this topic.

• Administer ORS until clinical dehydration is corrected, then continue to replace ongoing losses until diarrhea resolves 1
• For each watery stool, replace with approximately 200-400 mL of ORS 2
• ORS is as effective as intravenous therapy for mild to moderate dehydration 3

Nutritional Management

Resume a normal, age-appropriate diet immediately during or after rehydration—do not restrict food intake. 1

• Continue regular eating throughout the illness; early refeeding speeds recovery 1, 2
• Avoid foods high in simple sugars (soft drinks, undiluted apple juice) as they worsen diarrhea through osmotic effects 2
• Limit or avoid caffeinated beverages (coffee, tea, energy drinks) as caffeine stimulates intestinal motility and worsens symptoms 2

Pharmacological Considerations

Loperamide (Antimotility Agent)

Loperamide may be prescribed for immunocompetent adults with acute watery diarrhea, but only after adequate hydration. 1

• Maximum dose: 16 mg per day (initial 4 mg, then 2 mg after each unformed stool) 4, 5
• Absolute contraindications: fever, bloody diarrhea, suspected inflammatory diarrhea, or signs suggesting toxic megacolon 1, 4
• Loperamide should be avoided in elderly patients taking QT-prolonging medications (Class IA or III antiarrhythmics) 5
• Use caution with CYP3A4 inhibitors (itraconazole), CYP2C8 inhibitors (gemfibrozil), or P-glycoprotein inhibitors (quinidine, ritonavir), as these significantly increase loperamide exposure and cardiac risk 5

Antiemetics

• Ondansetron may be considered to facilitate oral rehydration if significant vomiting is present, though this is more commonly used in children over 4 years 1, 6
• Antiemetics are not a substitute for fluid therapy 1

Probiotics

• Probiotic preparations may be offered to reduce symptom severity and duration in immunocompetent adults 1, 2
• Specific strains, dosages, and formulations vary; consult product literature 1

What NOT to Prescribe

Avoid antimicrobial agents unless specific indications are present (bloody diarrhea, recent antibiotic use, recent foreign travel, immunodeficiency, or identified pathogen requiring treatment). 2 Viral agents cause approximately 70% of acute gastroenteritis cases, making antibiotics ineffective in most situations. 7

• Do not prescribe metoclopramide—it has no role in gastroenteritis management and may worsen outcomes by accelerating transit 2
• Avoid adsorbents, antisecretory drugs, and toxin binders—they do not reduce diarrhea volume or duration 2

Escalation Criteria

Switch to intravenous rehydration with isotonic fluids (lactated Ringer's or normal saline) if: 1

• Severe dehydration, shock, or altered mental status develops
• Oral rehydration therapy fails
• Ileus is present
• Patient cannot tolerate oral intake despite antiemetics

Red Flags Requiring Immediate Reevaluation

• High fever (>38.5°C) with bloody stools suggests dysentery; avoid loperamide and consider stool culture 1, 4
• Signs of severe dehydration (≥10% fluid deficit): altered mental status, prolonged skin tenting, poor perfusion 2
• Persistent symptoms beyond 48 hours without improvement warrant reassessment 5
• Development of abdominal distention or absent bowel sounds 5

Common Pitfalls to Avoid

• Do not delay rehydration while awaiting diagnostic testing—begin ORS immediately 2
• Do not use sports drinks or juices as primary rehydration solutions for moderate dehydration; low-osmolarity ORS is superior 2
• Do not prescribe loperamide before ensuring adequate hydration 1, 4
• Do not unnecessarily restrict diet—early refeeding improves outcomes 1, 2