What is the antibiotic of choice for bacterial diarrhea?

Antibiotic of Choice for Bacterial Diarrhea

Azithromycin is the preferred first-line antibiotic for bacterial diarrhea in most clinical scenarios, particularly for dysentery (bloody diarrhea) and when fluoroquinolone-resistant pathogens like Campylobacter are suspected. 1, 2

Treatment Algorithm by Clinical Presentation

For Dysentery (Bloody Diarrhea with Fever)

• Azithromycin is the drug of choice regardless of geographic region, given as either a single 1000 mg dose or 500 mg daily for 3 days 1, 2, 3
• This recommendation is based on superior efficacy against Shigella (the most common cause of dysentery), with studies showing 100% clinical cure rates and significant reduction in diarrhea duration compared to ciprofloxacin (32.4 hours shorter, RR 0.32) 1, 2
• Azithromycin also demonstrates excellent activity against Campylobacter, where fluoroquinolone resistance now reaches 19% globally 1, 4

For Acute Watery Diarrhea (Non-Bloody)

• Most cases do not require antibiotics unless the patient is severely ill, immunocompromised, or has recent international travel with high fever (≥38.5°C) 1, 3
• When treatment is indicated, azithromycin 500 mg single dose is preferred over fluoroquinolones due to better safety profile and effectiveness against resistant organisms 1, 2, 3
• Rifaximin 200 mg three times daily for 3 days is an alternative for non-invasive diarrhea (no fever, no blood), but fails in up to 50% of cases with invasive pathogens and should be avoided if dysentery is possible 1, 3

For Traveler's Diarrhea

• Azithromycin is first-line (single 1000 mg dose or 500 mg daily for 3 days) based on 2017 guidelines from the Journal of Travel Medicine 1, 2
• Fluoroquinolones (ciprofloxacin 750 mg single dose or 500 mg twice daily for 3 days) are alternatives only in regions with low Campylobacter resistance 1, 3
• The American College of Gastroenterology recommends antibiotics only when likelihood of bacterial pathogens is high enough to justify potential adverse effects 1

Pathogen-Specific Considerations

Shigella

• Azithromycin or ciprofloxacin are both effective, but azithromycin is increasingly preferred due to rising fluoroquinolone resistance 1, 4
• Beta-lactams (ceftriaxone) show superior efficacy to fluoroquinolones when Shigella is confirmed (RR 4.68 for treatment failure with fluoroquinolones) 1

Campylobacter

• Azithromycin is the drug of choice due to 19% fluoroquinolone resistance rates globally 1, 4
• Treatment is most effective when started early in the illness course 4

Non-typhoidal Salmonella

• Antibiotics are NOT routinely recommended for uncomplicated gastroenteritis, as they do not improve clinical outcomes and may prolong carriage 1
• Treatment is indicated only for: severe infection, age <6 months or >50 years, immunocompromised patients, or those with prosthetic devices, valvular heart disease, severe atherosclerosis, malignancy, or uremia 1
• When treatment is needed: ciprofloxacin, ceftriaxone plus azithromycin for severe cases, or trimethoprim-sulfamethoxazole if susceptible 1

Cholera

• Azithromycin single dose is superior to ciprofloxacin, reducing diarrhea duration by >1 day and clinical failure risk (RR 0.32) 1
• Alternative: doxycycline or tetracycline 1

Critical Safety Considerations

Why Azithromycin Over Fluoroquinolones

• Fluoroquinolones carry significant risks: FDA black box warning for Achilles tendon rupture, increased C. difficile infection risk, QT prolongation with potential fatal dysrhythmias, and acquisition of multidrug-resistant bacteria during travel 1, 3
• Azithromycin has minimal side effects (3% gastrointestinal complaints, mostly dose-related nausea) 1, 2
• Splitting the 1000 mg dose over the first day may reduce side effects without compromising efficacy 1

When to AVOID Antibiotics

• Never treat suspected STEC O157 or Shiga toxin-producing E. coli with antibiotics, as this increases risk of hemolytic uremic syndrome 1
• Avoid empiric treatment in immunocompetent patients with watery diarrhea without fever or recent international travel 1
• Do not treat asymptomatic contacts 1

Pediatric Modifications

• For infants <3 months with suspected bacterial etiology: third-generation cephalosporin (ceftriaxone) is preferred 1
• For older children with dysentery: azithromycin based on local susceptibility patterns and travel history 1, 4
• Fluoroquinolones should be avoided in pediatrics due to increased joint-related adverse events 5

Adjunctive Therapy

• Loperamide can be combined with azithromycin for faster symptomatic relief: 4 mg initially, then 2 mg after each liquid stool (maximum 16 mg/24 hours) 2, 3
• This combination further reduces gastrointestinal symptoms and illness duration 3
• Never use loperamide alone without antibiotics in dysentery or suspected invasive pathogens 2

When to Obtain Cultures

• Microbiologic testing is recommended for: severe illness, persistent symptoms (>14 days), bloody diarrhea, treatment failure, or returning travelers 1
• Empiric therapy should not be delayed while awaiting results in severely ill patients 1