Application of patient population-derived pharmacokinetic-pharmacodynamic relationships to tigecycline breakpoint determination for staphylococci and streptococci.

Correctly determined susceptibility breakpoints are important to both the individual patient and to society at large. A previously derived patient population pharmacokinetic model and Monte Carlo simulation (9999 patients) were used to create a likelihood distribution of tigecycline exposure, as measured by the area under the concentration-time curve at 24 h (AUC(24)). Each resultant AUC(24) value was paired with a clinically relevant fixed MIC value ranging from 0.12 to 2 mg/L. For each AUC(24)-MIC pair, the probability of microbiologic response was calculated using an exposure-response relationship, which was derived from patients with complicated skin and skin structure infections that involved Staphylococcus aureus or streptococci or both. The median probability of microbiologic success was 94% or greater for MIC values up to and including 0.25 mg/L. The median probability of microbiologic success was 66% or less for MIC values of 0.5 mg/L or greater. These data support a susceptibility breakpoint of 0.25 mg/L for S. aureus and streptococci.