Can you write a prescription for an adult with acute gastroenteritis (watery diarrhea, no blood or mucus, no high fever) including oral rehydration solution, ondansetron, loperamide, Saccharomyces boulardii, and conditional azithromycin or ciprofloxacin if fever >38.5 °C, bloody stool, severe abdominal pain, or symptoms >3 days?

Prescription for Acute Gastroenteritis

For an adult with uncomplicated acute gastroenteritis presenting with watery diarrhea, the prescription should prioritize oral rehydration solution as first-line therapy, with ondansetron to facilitate oral intake if vomiting is significant, and reserve antibiotics strictly for specific high-risk scenarios (fever >38.5°C with dysentery, bloody stools, or immunocompromised status). 1

Oral Rehydration Solution (ORS)

• Prescribe low-osmolarity ORS as the cornerstone of treatment 1, 2
• Dosing: 50-100 mL/kg over 2-4 hours for moderate dehydration (6-9% fluid deficit) 2
• Replace ongoing losses: 10 mL/kg for each watery stool 2
• Continue until clinical dehydration is corrected and diarrhea resolves 1
• ORS is as effective as intravenous therapy for mild-to-moderate dehydration and should be the first-line approach 1, 3

Ondansetron (Antiemetic)

• Ondansetron 8 mg orally once, may repeat in 8 hours if needed (maximum 16 mg/day) 1, 4
• Indication: Significant vomiting that impairs oral rehydration tolerance 1, 4
• Ondansetron facilitates oral rehydration compliance and decreases hospitalization rates 5, 6
• Administer only after initial assessment confirms no bloody diarrhea or high fever suggesting bacterial/inflammatory etiology 4
• Contraindications: Avoid in bloody diarrhea, fever suggesting bacterial gastroenteritis, or known QT prolongation 4

Loperamide (Antimotility Agent)

• Loperamide 4 mg initially, then 2 mg after each unformed stool (maximum 16 mg/day) 1
• Only for immunocompetent adults with acute watery diarrhea, once adequately hydrated 1
• Absolute contraindications: bloody diarrhea, high fever (>38.5°C), suspected inflammatory/bacterial diarrhea, or any concern for toxic megacolon 1
• Stop immediately if fever develops or stools become bloody 1

Probiotics (Saccharomyces boulardii)

• Saccharomyces boulardii 250-500 mg orally twice daily for 5-7 days 1, 2
• May reduce symptom severity and duration in immunocompetent adults 1
• Safe adjunctive therapy with minimal side effects 1

Conditional Antibiotic Therapy

Do NOT prescribe antibiotics empirically for uncomplicated watery diarrhea 1, 7. Antibiotics are indicated ONLY if specific criteria develop:

Azithromycin 500 mg orally daily for 3 days (or 1 gram single dose) IF:

• Fever ≥38.5°C PLUS bloody stools (dysentery pattern suggesting Shigella) 7
• Severe abdominal pain with systemic toxicity 7
• Symptoms persisting >3 days with fever and bloody stools 7
• Recent international travel to high-risk regions with fever ≥38.5°C or sepsis signs 7
• Immunocompromised status (HIV, transplant, chemotherapy) with severe illness and bloody diarrhea 7

Ciprofloxacin 500 mg orally twice daily for 3 days (alternative to azithromycin) IF:

• Same criteria as above, but azithromycin is preferred due to rising fluoroquinolone resistance 7
• Consider in regions with documented azithromycin resistance 7

Critical Antibiotic Contraindication:

• NEVER give antibiotics if Shiga toxin-producing E. coli (STEC/O157) is suspected, as this increases hemolytic uremic syndrome risk 7
• Suspect STEC with bloody diarrhea after consuming undercooked beef or unpasteurized dairy 7

Dietary Instructions

• Resume normal age-appropriate diet immediately during or after rehydration 1, 2
• Avoid caffeinated beverages (coffee, tea, energy drinks), alcohol, and foods high in simple sugars 2
• Continue regular meals; fasting or restrictive diets are not recommended 1, 2

Red Flags Requiring Immediate Re-evaluation

• Severe dehydration signs: altered mental status, prolonged skin tenting >2 seconds, cool extremities, decreased capillary refill 2
• Persistent vomiting despite ondansetron and small-volume ORS administration 2
• Development of bloody stools with fever 2, 7
• Signs of shock: hypotension, tachycardia unresponsive to oral fluids 1
• Absent bowel sounds (ileus) 2

Infection Control

• Practice rigorous hand hygiene with soap and water after toilet use, before eating, and after handling soiled items 1, 2
• Alcohol-based sanitizers are less effective against norovirus and some enteric pathogens 1
• Avoid food preparation for others until 48 hours after symptom resolution 2

Common Pitfalls to Avoid

• Do not prescribe antibiotics empirically for watery diarrhea without fever or blood 1, 7
• Do not use sports drinks or juices as primary rehydration—they lack appropriate electrolyte composition and have excessive sugar 2
• Do not give loperamide with any fever or bloody stools 1
• Do not delay ORS while awaiting diagnostic testing 2
• Do not use metoclopramide—it has no role in gastroenteritis management and may worsen diarrhea 2