Assessment of pharmacokinetics-pharmacodynamics to support omadacycline dosing regimens for the treatment of patients with acute bacterial skin and skin structure infections

ABSTRACT Pharmacokinetic-pharmacodynamic (PK-PD) relationships for efficacy were evaluated using data from omadacycline-treated patients with acute bacterial skin and skin structure infections (ABSSSI) enrolled in two phase 3 studies. Patients received omadacycline 100 mg intravenously (IV) every 12 hours for two doses, followed by 100 mg IV every 24 hours (q24h), with the option to switch to 300 mg oral (PO) q24h after 3 days or 450 mg PO q24h for two doses, followed by 300 mg PO q24h for a total duration of 7–14 days. Clinical response was evaluated at 48–72 hours early clinical response (ECR), end of treatment (EOT), and 7–14 days after EOT. Using a population pharmacokinetic (PK) model and PK data from patients with Staphylococcus aureus at baseline, omadacycline free-drug plasma area under the concentration-time curve (AUC) values were determined, and the relationships between free-drug plasma AUC:MIC ratio and dichotomous efficacy endpoints were evaluated. Using these relationships, the population PK model, simulation, and an omadacycline MIC distribution for S. aureus , mean percent probabilities of response were evaluated. Statistically significant PK-­PD relationships were identified for ECR ( P = 0.016 and 0.013 for optimized two- and three-group free-drug plasma AUC:MIC ratios, respectively). At an MIC value of 0.5 µg/mL, percent probabilities of model-predicted success for ECR based on the univariable PK-PD relationships using continuous and two-group free-drug plasma AUC:MIC ratio variables were 91.9 and 95.6%, respectively, for the IV-to-PO dosing regimen and 89.3 and 88.4%, respectively, for the PO-only dosing regimen. These data support for omadacycline IV-to-PO and PO-only dosing regimens for ABSSSI and an omadacycline susceptibility breakpoint of 0.5 µg/mL for S. aureus .