BACKGROUND: Antibiotic administration by subcutaneous (SC) injection is common practice in French geriatric wards as an alternative to the intravenous (IV) route, but few pharmacokinetic/pharmacodynamic data are available. Ertapenem is useful for the treatment of infections with ESBL-producing enterobacteria. OBJECTIVES: To report and compare ertapenem pharmacokinetic data between IV and SC routes in older persons. METHODS: Patients >65 years of age receiving ertapenem (1 g once daily) for at least 48 h (IV or SC, steady-state) were prospectively enrolled. Total ertapenem concentrations [residual (C0), IV peak (C0.5) and SC peak (C2.5)] were determined by UV HPLC. Individual-predicted AUC0-24 values were calculated and population pharmacokinetic analyses were performed. Using the final model, a Monte Carlo simulation involving 10 000 patients evaluated the influence of SC or IV administration on the PTA. Tolerance to ertapenem and recovery were also monitored. ClinicalTrials.gov identifier: NCT02505386. RESULTS: Ten (mean +/- SD age=87+/-7 years) and 16 (age=88+/-5 years) patients were included in the IV and SC groups, respectively. The mean C0 and C2.5 values were not significantly different between the IV and SC groups (C0=12+/-5.9 versus 12+/-7.4 mg/L, P=0.97; C2.5=97+/-42 versus 67+/-41 mg/L, P=0.99). The mean C0.5 was higher in the IV group compared with the SC group (C0.5=184+/-90 versus 51+/-66 mg/L, P=0.001). The mean individual AUCs (1126.92+/-334.99 mg.h/L for IV versus 1005.3+/-266.0 mg.h/L for SC, P=0.38) and PTAs were not significantly different between groups. No severe antibiotic-related adverse effects were noted. CONCLUSIONS: SC administration of ertapenem is an alternative to IV administration in older patients.Read less <