Clinical pharmacokinetics of 3-h extended infusion of meropenem in adult patients with severe sepsis and septic shock: implications for empirical therapy against Gram-negative bacteria

Background Optimal anti-bacterial activity of meropenem requires maintenance of its plasma concentration (Cp) above the minimum inhibitory concentration (MIC) of the pathogen for at least 40% of the dosing interval (fT > MIC > 40). We aimed to determine whether a 3-h extended infusion (EI) of meropenem achieves fT > MIC > 40 on the first and third days of therapy in patients with severe sepsis or septic shock. We also simulated the performance of the EI with respect to other pharmacokinetic (PK) targets such as fT > 4 x MIC > 40, fT > MIC = 100, and fT > 4 x MIC = 100. Methods Arterial blood samples of 25 adults with severe sepsis or septic shock receiving meropenem 1000 mg as a 3-h EI eight hourly (Q8H) were obtained at various intervals during and after the first and seventh doses. Plasma meropenem concentrations were determined using a reverse-phase high-performance liquid chromatography assay, followed by modeling and simulation of PK data. European Committee on Antimicrobial Susceptibility Testing (EUCAST) definitions of MIC breakpoints for sensitive and resistant Gram-negative bacteria were used. Results A 3-h EI of meropenem 1000 mg Q8H achieved fT > 2 mu g/mL > 40 on the first and third days, providing activity against sensitive strains of Enterobacteriaceae, Pseudomonas aeruginosa and Acinetobacter baumannii. However, it failed to achieve fT > 4 mu g/mL > 40 to provide activity against strains susceptible to increased exposure in 33.3 and 39.1% patients on the first and the third days, respectively. Modeling and simulation showed that a bolus dose of 500 mg followed by 3-h EI of meropenem 1500 mg Q8H will achieve this target. A bolus of 500 mg followed by an infusion of 2000 mg would be required to achieve fT > 8 mu g > 40. Targets of fT > 4 mu g/mL = 100 and fT > 8 mu g/mL = 100 may be achievable in two-thirds of patients by increasing the frequency of dosing to six hourly (Q6H). Conclusions In patients with severe sepsis or septic shock, EI of 1000 mg of meropenem over 3 h administered Q8H is inadequate to provide activity (fT > 4 mu g/mL > 40) against strains susceptible to increased exposure, which requires a bolus of 500 mg followed by EI of 1500 mg Q8H. While fT > 8 mu g/mL > 40 require escalation of EI dose, fT > 4 mu g/mL = 100 and fT > 8 mu g/mL = 100 require escalation of both EI dose and frequency.