Example of dosage individualization based on PK/PD in a patient treated with ertapenem as SAT for a relapsing PJI: 78-old woman who had a relapsing left prosthetic hip infection due to Enterobacter cloacae (only susceptible to ertapenem with a MIC of 0.064 mg/L) for whom iterative DAIR was done with persistence of the organism (panel A). Explantation was contraindicated as it was a revision prosthesis without loosening with a high risk of peroperative complication and loss of function (panel B). She received as primary antibiotics following the DAIR ertapenem at the conventional dose of 1 g/day. Subcutaneous administrations were firstly performed using a butterfly needle with injection each day in the right thigh of in the abdominal flanks (panel C), with secondary systemic diffusion of the drug in blood, and then at the site of infection. Ertapenem drug concentrations were measured, with three samples collected in red (panel D; the x-axis shows the time, the y axis represents the ertapenem plasma concentration at the steady-state; The blue marks on the x-axis show drug administrations): pre-dose, 30 min after the end of the 30 min SC infusion and 5 h post-dose. Ertapenem individual PK parameters were then estimated by a Bayesian approach based on our published population PK model of ertapenem implemented into the BestDose™ software. Panel D shows the results of the model fitting (black line for estimated concentrations during time), which was very good, and we simulated a future regimen with 1 g of ertapenem every 48 h. Our plasma concentration target for this patient was the bacterial MIC (0.064 mg/L) corrected for ertapenem protein binding (free fraction of 5%), resulting in 1.28 mg/L. We calculated that 1 g of ertapenem every 48 h would result in a trough concentration of 0.4 mg/L and 63% of time spent above the target after 48 h. While the optimal value would be 100%, this was considered acceptable, considering that 40% was reported to be sufficient to get a bactericidal effect with this agent [54].