Initial antimicrobial component of the regimen for all forms of systemic anthrax until susceptibility data available?

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A reliable, rapidly active agent against Bacillus anthracis is essential when systemic anthrax is suspected, because the disease can progress quickly and susceptibility results take time. Ciprofloxacin, a fluoroquinolone, fits this need well. It has proven bactericidal activity against B. anthracis by inhibiting DNA gyrase and topoisomerase IV, and it achieves good tissue penetration, making it effective across systemic forms of the infection. For this reason, it has long been the first-line initial antimicrobial component while awaiting susceptibility data. If ciprofloxacin cannot be used, doxycycline serves as a reasonable alternative, but ciprofloxacin remains the preferred starting option given the breadth of clinical data and guidelines supporting its use. Amoxicillin is less reliable as monotherapy for systemic anthrax due to variable susceptibility, and although other fluoroquinolones like levofloxacin may be considered in some settings, ciprofloxacin is the preferred initial choice because of its established efficacy in this disease context.