What is the recommended treatment for anthrax?

Treatment of Anthrax

For inhalational, gastrointestinal, and oropharyngeal anthrax, initiate intravenous ciprofloxacin 400 mg every 12 hours OR doxycycline 100 mg every 12 hours as first-line therapy, combined with one or two additional antimicrobials, for a total duration of 60 days (IV initially, then oral when clinically stable). 1

Treatment by Clinical Form

Inhalational Anthrax (Systemic Disease)

Initial IV Therapy:

• Adults: Ciprofloxacin 400 mg IV every 12 hours OR doxycycline 100 mg IV every 12 hours 1
• Children: Ciprofloxacin 10-15 mg/kg IV every 12 hours (max 1 g/day) OR doxycycline (weight-based: >45 kg = 100 mg q12h; <45 kg = 2.2 mg/kg q12h) 1
• Pregnant women: Same regimen as non-pregnant adults—the high mortality from infection outweighs antimicrobial risks 1

Critical Multi-Drug Requirement:

• Two or more antimicrobial agents are mandatory due to the high mortality associated with inhalational anthrax 1
• Additional agents with in vitro activity include rifampin, vancomycin, imipenem, chloramphenicol, clindamycin, and clarithromycin 1
• Avoid: Penicillin G and ampicillin as monotherapy due to potential beta-lactamase activity; cephalosporins and trimethoprim-sulfamethoxazole should not be used 1

Transition to Oral Therapy:

• Switch when clinically appropriate to ciprofloxacin 500 mg PO twice daily OR doxycycline 100 mg PO twice daily 1
• Total duration: 60 days (IV + oral combined) due to potential spore persistence after aerosol exposure 1

Cutaneous Anthrax

Uncomplicated Cases (No Systemic Signs):

• Adults: Ciprofloxacin 500 mg PO twice daily OR doxycycline 100 mg PO twice daily for 60 days 1
• Children: Ciprofloxacin 10-15 mg/kg PO every 12 hours (max 1 g/day) OR doxycycline (weight-based dosing) for 60 days 1
• Traditional 7-10 day courses are inadequate when concurrent aerosol exposure risk exists 1

Complicated Cases (Systemic Involvement):

• Use IV multi-drug regimen as for inhalational anthrax if any of the following are present: 1
  • Signs of systemic involvement
  • Extensive edema
  • Lesions on head or neck

Gastrointestinal and Oropharyngeal Anthrax

• Use the same regimens recommended for inhalational anthrax (IV multi-drug therapy for 60 days) 1

Special Populations

Pregnant Women

• Ciprofloxacin or doxycycline are recommended despite typical pregnancy contraindications 1
• After clinical improvement with penicillin-susceptible strains, amoxicillin 500 mg three times daily may be considered for prophylaxis completion 2
• Doxycycline adverse effects on teeth/bones are dose-related; short-term use (7-14 days) before 6 months gestation may be acceptable 1

Children ≤8 Years

• Tetracyclines (doxycycline) are recommended despite age, as the American Academy of Pediatrics endorses their use for serious infections 1
• Dosing: 2.2 mg/kg every 12 hours for doxycycline 1

Immunocompromised Patients

• Use same regimens as immunocompetent patients 1

Adjunctive Therapies

Corticosteroids:

• Consider for patients with severe edema, respiratory compromise, or meningitis 1
• Based on experience with bacterial meningitis of other etiologies 1

CNS Involvement:

• If meningitis is suspected, doxycycline may be suboptimal due to poor CNS penetration 1
• Prioritize ciprofloxacin or add agents with better CNS penetration 1

Critical Pitfalls to Avoid

1. Do not use monotherapy for systemic anthrax—multi-drug regimens are essential given high bacterial loads 1

2. Do not use penicillin/ampicillin alone—B. anthracis may harbor inducible beta-lactamases rendering these ineffective 1

3. Do not shorten duration to 7-10 days—60 days is required due to spore persistence and reactivation risk 1

4. Do not avoid fluoroquinolones/tetracyclines in pregnancy or children—mortality risk far exceeds medication risks 1, 2

5. Ensure adequate hydration with oral formulations to reduce esophageal irritation risk 3

FDA-Approved Indications

Both ciprofloxacin and doxycycline are FDA-approved for inhalational anthrax (post-exposure) to reduce incidence or progression of disease following aerosolized B. anthracis exposure 3, 4

Human serum concentrations achieved with standard dosing serve as surrogate endpoints reasonably likely to predict clinical benefit, based on rhesus monkey models where ciprofloxacin prophylaxis reduced mortality from 90% (9/10 placebo) to 11% (1/9 treated) 4