What is the appropriate prescription for a patient presenting to the OPD with acute gastroenteritis?

Management of Acute Gastroenteritis in the Outpatient Setting

For a patient presenting with acute gastroenteritis in the OPD, prescribe oral rehydration solution (ORS) as the primary treatment, with ondansetron if vomiting is significant, and reserve antibiotics only for specific bacterial pathogens confirmed by clinical features or testing. 1

Initial Assessment and Hydration Status

Evaluate dehydration severity through specific clinical signs rather than relying on laboratory tests:

• Mild dehydration (3-5% fluid deficit): Normal mental status, slightly dry mucous membranes, normal skin turgor 1
• Moderate dehydration (6-9% fluid deficit): Dry mucous membranes, decreased skin turgor with tenting when pinched, reduced urine output 1
• Severe dehydration (≥10% fluid deficit): Severe lethargy or altered consciousness, prolonged skin tenting (>2 seconds), cool extremities with poor capillary refill, rapid deep breathing 1

The most reliable clinical predictors are prolonged skin retraction time, abnormal capillary refill, and rapid deep breathing—more so than sunken fontanelle or absence of tears. 1, 2

Primary Treatment: Oral Rehydration Therapy

Prescribe low-osmolarity oral rehydration solution (ORS) as first-line therapy for all patients with mild to moderate dehydration. 1, 3

ORS Administration Protocol:

• For moderate dehydration: Administer 100 mL/kg ORS over 2-4 hours 1
• If vomiting is present: Start with small volumes (5-10 mL) every 1-2 minutes using a spoon or syringe, gradually increasing as tolerated 1, 3
• Replace ongoing losses: Give 10 mL/kg ORS for each watery stool and 2 mL/kg for each vomiting episode 1
• Reassess after 2-4 hours: If still dehydrated, reestimate deficit and restart rehydration 1

This approach successfully rehydrates >90% of patients without requiring intravenous therapy. 1

Antiemetic Therapy

Prescribe ondansetron for patients >4 years with significant vomiting that hinders oral rehydration. 1

Ondansetron reduces vomiting, improves oral intake success, decreases need for IV hydration, and shortens emergency department stays with minimal adverse effects. 4, 5, 2, 6, 7 While older guidelines discouraged routine antiemetic use, recent high-quality evidence has changed recommendations to support ondansetron when vomiting limits ORS tolerance. 5, 7

Do NOT prescribe metoclopramide—it is explicitly contraindicated in gastroenteritis as it accelerates gastrointestinal transit and has no demonstrated benefit. 1

Antimotility Agents

Loperamide may be prescribed for immunocompetent adults with acute watery diarrhea once adequately hydrated. 8, 1, 3

• Adult dosing: 4 mg initial dose, then 2 mg after each unformed stool (maximum 16 mg/day) 8
• Absolute contraindication: Never prescribe loperamide to children <18 years—serious adverse events including ileus and deaths have been reported 1, 3
• Avoid in: Bloody diarrhea, fever with systemic toxicity, or suspected inflammatory/invasive diarrhea 8, 3

Antibiotic Therapy: When and What to Prescribe

Most acute gastroenteritis is viral and does NOT require antibiotics. 1 Antimicrobial therapy should be reserved for specific clinical scenarios:

Indications for Antibiotics:

• Bloody diarrhea with fever: Suggests invasive bacterial pathogen (Shigella, Salmonella, Campylobacter, enterohemorrhagic E. coli) 8, 1
• Severe watery diarrhea in cholera-endemic areas: "Rice-water" stools with severe dehydration 9
• Immunocompromised patients: Lower threshold for empiric therapy 8
• Traveler's diarrhea with moderate-to-severe symptoms: Recent travel history with incapacitating diarrhea 8

Antibiotic Selection Algorithm:

For dysentery (bloody diarrhea + fever):

• First-line: Azithromycin 1000 mg single dose or 500 mg daily for 3 days 8
• Alternative: Ciprofloxacin 750 mg single dose or 500 mg twice daily for 3 days 8
• Note: Azithromycin is preferred in Southeast Asia and India due to fluoroquinolone-resistant Campylobacter 8

For suspected cholera:

• First-line: Doxycycline 300 mg single oral dose (adults) or 6 mg/kg (children) 9
• Alternative: Azithromycin 1 g single dose (adults) or 20 mg/kg (children, max 1 g) 9
• Start immediately without waiting for laboratory confirmation in outbreak settings 9

For traveler's diarrhea (non-dysenteric):

• First-line: Azithromycin 1000 mg single dose 8
• Alternative: Ciprofloxacin 750 mg single dose or levofloxacin 500 mg single dose 8
• For mild-moderate cases: Rifaximin 200 mg three times daily for 3 days (only for non-invasive diarrhea) 8

Do NOT prescribe doxycycline empirically—it is no longer recommended for routine gastroenteritis due to widespread resistance, except for confirmed cholera. 9

Dietary Management

• Continue breastfeeding throughout the illness in infants 1, 3
• Resume age-appropriate diet during or immediately after rehydration—early refeeding reduces illness duration 1, 3
• Avoid: Caffeinated beverages (coffee, tea, energy drinks), high-sugar drinks (undiluted apple juice, sodas), alcohol, and spicy foods—these worsen diarrhea through osmotic effects and increased motility 8, 1
• Consider temporary dairy restriction (except yogurt and firm cheeses) as lactose intolerance may develop transiently 8

Adjunctive Therapies

Probiotics (Lactobacillus GG or Saccharomyces boulardii) may be prescribed to reduce symptom severity and duration. 1, 7

Zinc supplementation is only beneficial in children 6 months to 5 years in areas with high zinc deficiency or malnutrition—not routinely indicated in developed countries. 1, 7

Smectite or racecadotril may be considered as adjunctive therapy in Europe, though evidence is primarily from outside Europe. 7

Red Flags Requiring Referral or Hospitalization

Send patients for immediate evaluation if they develop:

• Severe dehydration signs: Altered mental status, prolonged skin tenting >2 seconds, cool extremities, rapid deep breathing 1
• Failure of oral rehydration: Persistent vomiting despite ondansetron and small-volume ORS administration 1
• Bloody stools with fever and systemic toxicity: Requires stool culture and possible hospitalization 1
• High-risk populations: Infants <3 months, elderly ≥65 years, immunocompromised patients—lower threshold for referral 1
• Absent bowel sounds: Absolute contraindication to oral rehydration 1

Infection Control Instructions

Provide clear discharge instructions on:

• Hand hygiene: Wash hands after toilet use, before eating, after handling soiled items 1
• Isolation: Keep patient away from others until at least 2 days after symptom resolution 1
• Surface disinfection: Clean contaminated surfaces promptly 1

Common Pitfalls to Avoid

• Do not delay rehydration while awaiting diagnostic testing—start ORS immediately 1
• Do not use sports drinks or apple juice as primary rehydration for moderate-severe dehydration—they lack appropriate electrolyte composition 1
• Do not prescribe antimotility agents to children or patients with bloody diarrhea 1, 3
• Do not prescribe antibiotics empirically without clear indication—most cases are viral 1
• Do not restrict diet unnecessarily—early refeeding improves outcomes 1, 3
• Do not underestimate dehydration in elderly patients—they may not manifest classic signs and have higher mortality risk 1