In panel B the same data are placed on a stylized version of a pharmacokinetic plot in which drug is given to volunteers at time zero and then serum concentrations are measured at various times. MIC and MPC define the boundaries of the mutant selection window. This depiction of the window provides a straightforward explanation for the development of de novo resistance. Drug concentrations are commonly placed above MIC to have an effect on pathogen growth. At the same time, drug costs and toxic side effects tend to keep the drug concentrations low. The net result is that antimicrobials are often dosed such that their concentrations fall inside the mutant selection window. That makes mutant enrichment an inevitable consequence of dosing-to-cure strategies.