What is the best antibiotic for a patient with diarrhea and vomiting?

Antibiotics Are Generally NOT Recommended for Uncomplicated Diarrhea and Vomiting

Most cases of acute diarrhea and vomiting do not require antibiotic therapy, as viral pathogens are the predominant cause and antibiotics provide no benefit while increasing risks of adverse effects and antimicrobial resistance. 1, 2

When Antibiotics Should Be Avoided

• Never use antibiotics for routine acute watery diarrhea without specific indications, as the vast majority of infectious diarrhea episodes are self-limited and viral in origin 1, 2

• Avoid antimicrobials in suspected STEC O157 and other STEC producing Shiga toxin 2, as fluoroquinolones, β-lactams, TMP-SMX, and metronidazole are associated with evidence of harm including increased risk of hemolytic uremic syndrome 1

• Do not give antimotility drugs (loperamide) to children <18 years of age with acute diarrhea, as serious adverse events including ileus and deaths have been reported 1, 2

Specific Indications Where Antibiotics ARE Recommended

Dysentery (Bloody Diarrhea with Fever)

Azithromycin is the first-line antibiotic for dysentery regardless of geographic region due to widespread fluoroquinolone resistance in Campylobacter, Shigella, and Salmonella species 1

• Azithromycin dosing for dysentery: Single 1-gram dose OR 500 mg daily for 3 days 1, 3
• Azithromycin demonstrates superior clinical cure rates compared to levofloxacin in settings with high fluoroquinolone-resistant Campylobacter (>90% resistance rates) 1
• Effective against Shigella, enteroinvasive E. coli, Aeromonas, Plesiomonas, and Yersinia enterocolitica 1

Severe Illness in Immunocompromised Patients

• Empiric antibacterial treatment should be considered in immunocompromised patients with severe illness and bloody diarrhea (strong recommendation, low quality evidence) 1
• Immunocompromised hosts include those on immunosuppressive therapy, HIV-infected, transplant recipients, or with malignancy 1

Suspected Enteric Fever with Sepsis

• Patients with clinical features of sepsis suspected of having enteric fever should receive empiric broad-spectrum antimicrobial therapy after blood, stool, and urine culture collection 1
• Narrow antimicrobial therapy when susceptibility results become available 1

Acute Watery Diarrhea (Selected Cases Only)

For severe acute watery diarrhea in travelers or military personnel where rapid symptom resolution is operationally critical, single-dose antibiotic regimens are effective 1, 3, 4:

• Azithromycin 500 mg single dose for acute watery diarrhea 1, 3, 4
• Alternative: Levofloxacin 500 mg single dose OR Ciprofloxacin 750 mg single dose (but avoid in areas with high Campylobacter resistance) 1, 3
• Alternative: Rifaximin 200 mg three times daily for 3 days (but NOT for invasive/febrile illness) 1, 3

Critical Management Priorities Beyond Antibiotics

Rehydration is the Cornerstone of Treatment

• Reduced osmolarity oral rehydration solution (ORS) is first-line therapy for mild to moderate dehydration in all age groups 1, 2

• Administer 50-100 mL/kg ORS over 2-4 hours for moderate dehydration 2

• Replace ongoing losses: 10 mL/kg ORS for each watery stool, 2 mL/kg for each vomiting episode 2

• Isotonic intravenous fluids (lactated Ringer's or normal saline) are required for severe dehydration, shock, altered mental status, or failure of oral rehydration 1, 2, 5

Nutritional Management

• Continue breastfeeding throughout the diarrheal episode in infants 1, 2
• Resume age-appropriate diet during or immediately after rehydration rather than prolonged fasting 1, 2

Symptomatic Treatment Considerations

• Loperamide may be given to immunocompetent adults with acute watery diarrhea once adequately hydrated, but is contraindicated in children <18 years 1, 2
• Ondansetron may be given to children >4 years to facilitate oral rehydration when vomiting is significant 2
• Ancillary treatments are not substitutes for fluid and electrolyte therapy 1

Common Pitfalls to Avoid

• Do not delay rehydration while awaiting diagnostic testing or culture results - begin ORS immediately 2
• Do not use antibiotics empirically for all bloody diarrhea - STEC infections require avoidance of antimicrobials 1
• Do not assume fluoroquinolones remain effective globally - Campylobacter fluoroquinolone resistance exceeds 90% in many regions including Thailand and is increasing worldwide 1
• Do not use sports drinks, apple juice, or other high-sugar beverages as primary rehydration solutions - they can worsen diarrhea through osmotic effects 2
• Recognize that antibiotics themselves cause diarrhea in 7-33% of adults and up to 80% of pediatric patients, with third-generation cephalosporins, clindamycin, and fluoroquinolones showing strongest association 6, 7

When to Obtain Stool Studies

• Bloody diarrhea with fever and systemic toxicity 1, 2
• Recent antibiotic use (evaluate for C. difficile) 2
• Recent foreign travel 2
• Immunodeficiency 2
• Severe dehydration requiring hospitalization 1
• Diarrhea persisting beyond 48 hours despite supportive treatment 5