What is the recommended treatment for Shigella infections?

Treatment of Shigella Infections

The recommended first-line treatment for Shigella infections is ciprofloxacin at a dose of 500mg twice daily for 3-7 days for adults, with alternative options including TMP-SMX or azithromycin based on susceptibility patterns. 1

First-line Treatment Options

• Ciprofloxacin is the preferred first-line agent for treating Shigella infections in adults at a dose of 500mg twice daily for 3-7 days 1
• For adults, TMP-SMX is an alternative first-line treatment option at a dose of 160mg TMP and 800mg SMX twice daily for 5 days, if the strain is susceptible 1, 2
• Azithromycin is another alternative treatment option for adults at a dose of 500mg on day 1, followed by 250mg once daily for 4 days, particularly for resistant strains 1
• For children, TMP-SMX can be used at a dose of 10mg/kg/day TMP and 50mg/kg/day SMX in two divided doses for 5 days, if the strain is susceptible 3, 2

Treatment Algorithm

1. Initial antibiotic selection:

   • Base initial antibiotic choice on local susceptibility patterns 1
   • For travel-acquired cases, consider high rates of TMP-SMX resistance 3, 1
   • Fluoroquinolones are preferred as first-line when resistance patterns are unknown 3, 1

2. Monitoring response:

   • Assess clinical response within 2 days of starting treatment 3
   • If no improvement occurs within 2 days, change to an alternative antibiotic 3
   • If no improvement after an additional 2 days with second antibiotic, refer for stool microscopy to rule out amebiasis 3

3. Alternative treatments for resistant strains:

   • Nalidixic acid: 55 mg/kg/day in four divided doses for 5 days 3
   • Tetracycline: 50 mg/kg/day in four divided doses for 5 days 3
   • Ceftriaxone or other expanded-spectrum cephalosporins for resistant strains 3, 4

Special Considerations

• For Shigella bacteremia, extend treatment to 14 days using the same agents 3, 1
• All HIV-associated Shigella infections should be treated due to higher risk of complications 3
• HIV-infected persons have higher rates of adverse effects related to TMP-SMX 3
• For patients with CD4+ counts >200 cells/μL and mild disease, 7-14 days of treatment is reasonable; for advanced HIV disease (CD4+ <200 cells/μL), longer courses (2-6 weeks) are often recommended 3

Antibiotic Resistance Concerns

• Multiresistant strains of Shigella are widespread globally, complicating treatment selection 1, 5
• Periodic antibiotic susceptibility testing is advisable in endemic and epidemic settings 3
• Resistance mechanisms include decreased cellular permeability, active efflux pumps, drug-modifying enzymes, and target modification by mutation 5
• Surveillance data has demonstrated increasing resistance to first-line antibiotics such as ampicillin and TMP-SMX 4

Common Pitfalls and Caveats

• Mass prophylaxis or prophylaxis of family members is not recommended as a control measure for shigellosis 3
• Amebic dysentery tends to be misdiagnosed as shigellosis; consider amebiasis if two different antibiotics for shigellosis fail to improve symptoms 3
• Antimotility agents are contraindicated in shigellosis as they may worsen the clinical course 6
• Follow-up stool cultures are generally not required if complete clinical response has been demonstrated, except for food service workers or healthcare workers 1
• As few as 10-100 organisms can cause disease, making shigellosis highly contagious and requiring careful attention to hand hygiene for prevention 7