What should be the initial treatment for an adult patient with acute gastroenteritis characterized by persistent vomiting and diarrhea?

Initial Treatment for Acute Gastroenteritis in Adults

Begin with oral rehydration solution (ORS) as first-line therapy for mild to moderate dehydration, reserving intravenous fluids only for severe dehydration, shock, altered mental status, or failure of oral rehydration. 1, 2

Immediate Assessment and Rehydration Strategy

Evaluate Hydration Status

• Assess clinical signs: skin turgor, mental status, mucous membrane moisture, capillary refill, and vital signs 2
• Categorize dehydration severity:
  • Mild (3-5%): Minimal clinical signs
  • Moderate (6-9%): Loss of skin turgor, dry mucous membranes, decreased urine output
  • Severe (≥10%): Altered mental status, prolonged capillary refill, hypotension, tachycardia 2

Oral Rehydration Protocol

• For mild to moderate dehydration: Administer reduced osmolarity ORS until clinical dehydration is corrected 1, 2
• Start with small, frequent volumes (5-10 mL every 1-2 minutes) if vomiting is present, gradually increasing as tolerated 2, 3
• For moderate dehydration specifically: Give 100 mL/kg ORS over 2-4 hours 2
• Continue ORS to replace ongoing losses (10 mL/kg for each watery stool, 2 mL/kg for each vomiting episode) until diarrhea and vomiting resolve 1, 2
• Avoid sports drinks or juices as primary rehydration solutions—low-osmolarity ORS formulations are superior 2

Intravenous Rehydration Indications

Reserve IV therapy for: 1, 2

• Severe dehydration (≥10% fluid deficit)
• Shock or altered mental status
• Failure of oral rehydration therapy
• Ileus (absent bowel sounds)
• Intractable vomiting despite antiemetics

Use isotonic fluids (lactated Ringer's or normal saline) and continue until pulse, perfusion, and mental status normalize, then transition to ORS for remaining deficit 1, 2

Pharmacological Management

Antiemetic Therapy

• Ondansetron may be given to facilitate oral rehydration when vomiting is significant 1, 3
• Administer after adequate hydration is achieved 3
• Avoid in patients with bloody diarrhea or fever suggesting bacterial/inflammatory diarrhea 3

Antimotility Agents

• Loperamide may be given to immunocompetent adults with acute watery diarrhea once adequately hydrated 1, 2
• Initial dose: 4 mg followed by 2 mg after each unformed stool (maximum 16 mg daily) 4
• Absolutely avoid loperamide in suspected or proven inflammatory diarrhea, bloody diarrhea with fever, or when toxic megacolon is a concern 1

Antimicrobial Therapy

• In most adults with acute watery diarrhea without recent international travel, empiric antimicrobial therapy is NOT recommended 1
• Exceptions: immunocompromised patients, bloody diarrhea with fever/systemic toxicity, or suspected enteric fever 1

Nutritional Management

• Resume age-appropriate usual diet during or immediately after rehydration begins—do not delay feeding 1, 2
• Early refeeding reduces severity and duration of illness 2
• Avoid foods high in simple sugars (soft drinks, undiluted apple juice) as they exacerbate diarrhea through osmotic effects 2
• Limit or avoid caffeine and alcohol as they worsen symptoms through stimulation of intestinal motility 1, 2

Critical Pitfalls to Avoid

• Do not delay rehydration while awaiting diagnostic testing—begin ORS immediately 2
• Do not use antimotility drugs, adsorbents, antisecretory drugs, or toxin binders as primary therapy—they do not reduce diarrhea volume or duration 2, 3
• Do not unnecessarily restrict diet during or after rehydration 2
• Do not give loperamide in bloody diarrhea, fever suggesting bacterial infection, or suspected inflammatory conditions 1, 4
• Do not use inappropriate fluids (sports drinks, juices) as primary rehydration for moderate to severe dehydration 2

Monitoring and Reassessment

• Reassess hydration status after 2-4 hours of ORS administration 2
• If still dehydrated, reestimate deficit and restart rehydration protocol 2
• Monitor vital signs, urine output, and clinical signs of improvement 2
• Seek immediate medical evaluation if patient develops severe dehydration signs, altered mental status, persistent vomiting despite small-volume ORS, or bloody stools with fever 2, 3