FIG. 5.

Effect of dose schedule on efficacy of ciprofloxacin against B. anthracis. A ciprofloxacin exposure of an AUC₂₄ of mg · h/liter (AUC₂₄/MIC = 256) was given as two equal doses at 12-h intervals or as a single dose at 24-h intervals. The twice-daily regimen substantially reduced the total culture density and no resistant organisms were observed. Daily dosing prevented culture growth for 2 days, but the culture density increased to near control levels thereafter. Resistant organisms emerged after 1 day and replaced the susceptible organisms in the culture by day 2. The growth of an untreated control is also shown.