Population Pharmacokinetics of Piperacillin in the Early Phase of Severe Sepsis - Does Standard Dosing Result in Therapeutic Plasma Concentrations?

Appropriate empiric antibiotic therapy is crucial for reducing mortality in septic patients. Pathophysiological changes associated with the septic process, i.e. changes in volume of distribution (Vd), protein binding and drug clearance (Cl), lead to pharmacokinetic (PK) alterations that may influence the efficacy of the drug. As a consequence, antibiotic plasma concentrations are variable and hard to predict in this patient population. Optimal dosing and exposure can therefore be a challenge and standard antibiotic dosing regimens may result in subtherapeutic concentrations and therapeutic failure. Appropriate dosing is also essential in order to maximize bacterial killing and minimize development of antimicrobial resistance.

Piperacillin/tazobactam is a β-lactam-β-lactamase inhibitor combination with extended-spectrum antibacterial activity, which is often used for empirical treatment of severe infections. The antibacterial activity is time-depentent, i.e. the activity is related to the time for which the free unbound drug concentration is maintained above the minimum inhibitory concentration (MIC) (fT>MIC). By maximizing T>MIC, therapeutic impact increases and the risk of drug resistance development is reduced (7). For β-lactams, a fT>MIC of at least 50% is associated with clinical efficacy. However, higher targets may be needed for maximal bactericidal effect in critically ill patients. Piperacillin/tazobactam is by standard practice administered as intermittent bolus infusion (IB). However, prolonged infusion, both extended infusion (IE) and continuous infusion (CI) is believed to optimize drug exposure and has a PK advantage compared to IB.

Patients with known or suspected sepsis or severe sepsis, treated empirically with piperacillin/tazobactam 4g/0,5g (Tazocin®) every eight hour (q8h) were eligible for the study. Piperacillin/tazobactam (4g/0,5g) was administered intravenously (i.v.) as a 3-minute bolus infusion . Serial blood samples were collected over one dosing interval for up to three consecutive days if piperacillin/tazobactam treatment was maintained.

The free concentrations of piperacillin in sera were assessed using ultra high performance liquid chromatography (UHPLC).

Clinical MIC breakpoints according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) for Pseudomonas aeruginosa were used to evaluate the following PK/PD targets: 100% f T>MIC and 50% fT>MIC.