What is the dose of azithromycin (Zithromax) for bacterial gastroenteritis?

Azithromycin Dosing for Bacterial Gastroenteritis

For bacterial gastroenteritis, azithromycin should be dosed at 1,000 mg as a single dose OR 500 mg once daily for 3 days, with the single-dose regimen preferred for improved compliance. 1

Recommended Dosing Regimens

First-Line Dosing Options

• Single-dose regimen: 1,000 mg (1 gram) orally as a single dose 1

  • This is the preferred approach for travelers' diarrhea with dysentery and provides therapeutic tissue concentrations for approximately 10 days due to azithromycin's prolonged tissue half-life 1
  • Single-dose regimens have the advantage of improved compliance and allow for directly observed therapy 2

• Multi-day regimen: 500 mg once daily for 3 days 1

  • This is an equally effective alternative dosing strategy for bacterial gastroenteritis 1

Alternative Regimen for Severe Cases

• For enteric fever (typhoid/paratyphoid), a more intensive regimen may be warranted: 1,000 mg on day 1 (as single or divided dose), followed by 500 mg once daily for 5-6 additional days 3

Clinical Evidence Supporting Use

Azithromycin demonstrates excellent activity against common gastroenteritis pathogens, including Campylobacter, Salmonella, Shigella, and Yersinia species 4, 5. The drug achieves tissue concentrations that exceed serum concentrations by up to 100-fold, with high concentrations maintained in the gastrointestinal tract 6.

• In areas with ciprofloxacin-resistant Campylobacter (increasingly common worldwide), azithromycin is superior to ciprofloxacin in eradicating the organism and equally effective in shortening illness duration 5
• Against enteritis-producing pathogens, azithromycin shows MIC50 and MIC90 values of 4 and 12 mg/L respectively, making it a good empirical option 4

Administration Considerations

• Timing with food: Azithromycin should be taken on an empty stomach when possible, as food decreases bioavailability by approximately 50% 7
• Antacid interactions: Avoid concurrent administration with aluminum or magnesium-containing antacids, which reduce absorption 2
• Directly observed first dose is recommended when feasible to maximize compliance 2

Common Pitfalls and Safety Considerations

Cardiac Screening

• Perform an ECG before initiating therapy in patients with cardiac risk factors to assess QTc interval 1
• Avoid azithromycin if QTc >450 ms (men) or >470 ms (women) 1

Expected Side Effects

• Gastrointestinal symptoms (nausea, vomiting, abdominal pain, diarrhea) occur in approximately 3% of patients but are less frequent than with erythromycin 1, 2
• These symptoms typically resolve without intervention 1

When to Reassess

• Evaluate clinical response at days 5-7; improvement in symptoms should be evident by this time 1
• If no improvement occurs, consider alternative diagnoses or resistant organisms 1

Pediatric Dosing

For children with bacterial gastroenteritis, the dosing differs from adults and should be weight-based, though specific gastroenteritis dosing is not explicitly detailed in the provided guidelines. The general pediatric principle is 10 mg/kg on day 1, followed by 5 mg/kg daily for days 2-5 2.