Cost-benefit PK/PD relationship for increasing polymyxin B exposure against 03-149.01. Benefit (blue line) was defined as the initial bacterial killing of the total population within the first 24 h. Cost (red line) was the amplification of resistant subpopulations, which was based upon real-time PAP data over 336 h that tracked A. baumannii growth on agar containing polymyxin B at 3, 4, 6, 8, and 10 mg/liter. The intersecting fAUC for the drug exposure at which the benefit of bacterial killing equaled the cost of resistance amplification was 38.5 mg · h/liter.