What are the current guidelines for evaluating and managing acute diarrhea, including rehydration, diet, antidiarrheal agents, antibiotics, and red‑flag criteria?

Management of Acute Diarrhea

Oral rehydration solution (ORS) is the first-line therapy for mild to moderate dehydration in all patients with acute diarrhea, and most cases do not require antibiotics or diagnostic testing. 1, 2, 3

Initial Assessment and Risk Stratification

Assess hydration status by evaluating:

• Mild dehydration (3-5% fluid deficit): Increased thirst, slightly dry mucous membranes, normal vital signs 2, 3
• Moderate dehydration (6-9% fluid deficit): Decreased skin turgor, dry mucous membranes, sunken eyes, decreased urine output, orthostatic changes 2, 3
• Severe dehydration (≥10% fluid deficit): Altered mental status, weak or absent pulse, poor perfusion, shock 2, 4

Note that in severely malnourished children, sunken eyes and skin turgor are unreliable indicators. 5

Rehydration Therapy

Mild to Moderate Dehydration

Administer reduced osmolarity ORS (total osmolarity <250 mmol/L) as first-line therapy at 100 mL/kg over 2-4 hours. 1, 2, 3

The WHO-recommended formulation contains approximately Na 90 mM, K 20 mM, Cl 80 mM, HCO₃ 30 mM, and glucose 111 mM. 3 Start with small volumes (e.g., one teaspoon) and gradually increase as tolerated. 2

Replace ongoing stool losses with ORS: 2, 4

• Children <10 kg: 60-120 mL per diarrheal stool or vomiting episode (up to ~500 mL/day)
• Children >10 kg: 120-240 mL per episode (up to ~1 L/day)
• Adolescents and adults: Ad libitum, up to ~2 L/day

For patients who cannot tolerate oral intake, nasogastric administration of ORS may be considered. 1, 3, 4

Severe Dehydration

Administer isotonic intravenous fluids (lactated Ringer's or normal saline) immediately for severe dehydration, shock, altered mental status, or failure of ORS therapy. 1, 2, 3, 4

Continue IV rehydration until pulse, perfusion, and mental status normalize, then transition to ORS for remaining deficit replacement. 1, 4 In patients with ketonemia, initial IV hydration may be needed to enable tolerance of oral rehydration. 1

Nutritional Management

Resume age-appropriate usual diet during or immediately after rehydration is completed—do not withhold food. 1, 2, 3, 4 Early realimentation prevents malnutrition and may reduce stool output. 3

Continue breastfeeding throughout the diarrheal episode in infants and children. 1, 2, 3, 4

Administer oral zinc supplementation (10-20 mg daily for 10-14 days) to children 6 months to 5 years of age in countries with high zinc deficiency prevalence or with signs of malnutrition. 1, 3, 4

Antimicrobial Therapy

Empiric antibiotics are NOT recommended for most patients with acute watery diarrhea without recent international travel. 3, 4

Indications for Empiric Antimicrobial Therapy

Consider antibiotics ONLY in these specific circumstances: 1, 3, 4

• Immunocompromised patients with severe illness
• Ill-appearing infants <3 months with suspected bacterial etiology
• Bloody diarrhea with presumptive shigellosis (fever, abdominal pain, tenesmus)
• Recent international travelers with fever ≥38.5°C or signs of sepsis
• Clinical features of sepsis with suspected enteric fever

Administer broad-spectrum IV antimicrobials immediately after obtaining blood, stool, and urine cultures in patients with suspected enteric fever and sepsis. 4

Critical Contraindication

Never administer antimicrobials in STEC O157 or other Shiga toxin 2-producing E. coli infections—this increases the risk of hemolytic uremic syndrome. 1, 3, 4

Modify or discontinue antimicrobial treatment when a specific pathogen is identified. 1, 4

Adjunctive Therapies

Antimotility Agents

Never give antimotility drugs (loperamide) to children <18 years of age with acute diarrhea. 1, 2, 3, 4

Loperamide may be given to immunocompetent adults with acute watery diarrhea ONLY after adequate hydration, but must be avoided in any patient with bloody diarrhea, fever, or suspected inflammatory diarrhea due to risk of toxic megacolon. 1, 3, 4

Antiemetics

Ondansetron may be given to children >4 years of age and adolescents with acute gastroenteritis associated with vomiting to facilitate oral rehydration. 1, 2, 3, 4

Probiotics

Probiotic preparations may be offered to reduce symptom severity and duration in immunocompetent adults and children with infectious or antimicrobial-associated diarrhea. 1, 3, 4

Red-Flag Criteria Requiring Hospitalization

Admit patients with: 5

• Age <3 months
• Severe dehydration requiring IV fluids
• Severe malnutrition
• Toxic appearance or altered mental status
• Persistent vomiting despite ORS
• Suspected surgical abdomen
• Signs of sepsis

Seek immediate medical attention if: 2

• Patient becomes unable to tolerate oral fluids
• Signs of dehydration worsen despite treatment
• Diarrhea becomes bloody
• Fever increases significantly

Common Pitfalls to Avoid

Do not administer antimotility agents to children or in cases of bloody/inflammatory diarrhea—this can precipitate toxic megacolon. 4

Do not use antimicrobials for routine acute watery diarrhea—most cases are viral and self-limited. 4

Do not neglect rehydration while focusing on antimicrobial therapy—dehydration is the primary cause of morbidity and mortality. 4

Do not withhold food during diarrheal episodes—early refeeding is essential. 4

Do not use homemade sugar-salt solutions for established dehydration—the three-finger pinch method produces dangerously inconsistent sodium concentrations. 6 Use commercial ORS formulations instead.

Reassessment and Follow-up

Reassess hydration status after 2-4 hours of rehydration therapy. 2 Continue ORS maintenance fluids and replace ongoing losses until diarrhea and vomiting resolve. 1, 4