Population Pharmacokinetic Analysis of Piperacillin/Tazobactam in Korean Patients with Acute Infections

Cefepime, not Piperacillin/Tazobactam use, for empirical treatment of bloodstream infections caused by Enterobacter spp.: Results from a population pharmacokinetic/pharmacodynamic analysis

OBJECTIVE

There is a paucity of published data to evaluate the efficacy and safety of imipenem, cefepime and piperacillin/tazobactam dosing regimens against bloodstream infections caused by Klebsiella aerogenes (BSIs-Kae) and Enterobacter cloacae complex (BSIs-Ecc) in patients with various degrees of renal function.

METHODS

Pathogens were isolated from China's blood bacterial resistant investigation network. The dosing regimens of imipenem, cefepime and piperacillin were simulated with intermittent infusion and extended infusion. Monte Carlo simulation was performed to calculate the probability of target attainment and a cumulative fraction of response (CFR) against BSIs-Kae/Ecc.

RESULTS

In total, 203 BSIs-Kae, and 785 BSIs-Ecc were isolated from the surveillance network. Imipenem showed the highest in vitro activity against BSIs-Kae/Ecc, followed by cefepime (85%) and piperacillin/tazobactam (70-80%). The MIC₉₀ values of imipenem, cefepime and piperacillin/tazobactam aginst BSIs-Kae and BSIs-Ecc were 1/1 mg/L, 16/16 mg/L, and 64/128 mg/L, respectively. The simulation results showed imipenem achieved the highest CFRs in patients with normal or decreased renal function, with values of 91-99%, followed by FEP (88-96%), without risk of excessive dosing. However, the intermittent and extended dosing regimens of piperacillin/tazobactam were unlikely to provide adequate exposure for empirical management of BSIs-Kae/Ecc (CFRs, 50-80%), regardless of renal function. Besides, the traditional intermittent piperacillin/tazobactam dosing regimens were highly likely to contribute to suboptimal therapeutic exposure when MIC was close to clinical breakpoints.

CONCLUSIONS

Cefepime, not piperacillin/tazobactam, can be a reasonable carbapenem-sparing option in empirically treating BSIs-Kae/Ecc.

Optimal antipseudomonal ꞵ-lactam drug dosing recommendations in critically-ill Asian patients receiving CRRT

INTRODUCTION

The average body weight is smaller in Asian patients compared with Western patients, but influence of body weight in antibiotic dosing is unknown. This study was to predict the optimal ceftazidime, cefepime, meropenem, piperacillin/tazobactam doses in Asian patients undergoing continuous venovenous hemofiltration (CVVH).

METHODS

Monte Carlo simulations (MCS) were performed using published Asian demographics and pharmacokinetics parameters in 5000 virtual patients at three CVVH effluent rates (Qeff; 20, 30, 40 mL/kg/h). Various dosing regimens were assessed for the probability of target attainments using 60% fT > 1 × MIC or 4xMIC and neurotoxicity risk at 48-h using suggested neurotoxicity thresholds.

RESULTS

Ceftazidime 1 g q12h, meropenem 1 g q12h, and piperacillin/tazobactam 3.375 g q6h were optimal for all Qeff settings against fT > 1 × MIC. Cefepime 2 g q24h and 2 g q12h were optimal at 20 and 30-40 mL/kg/h respectively. For the aggressive PD target (4 × MIC), optimal ceftazidime regimens were 1.25 g q8h (20-30 mL/kg/h) and 1.5 g q8h (40 mL/kg/h). Cefepime 2 g q8h and meropenem 1 g q8h were optimal at all Qeff settings. No simulated piperacillin doses attained the aggressive PD target. Increased neurotoxicity risk was predicted with ceftazidime and cefepime doses attaining the efficacy.

CONCLUSION

MCS enabled the prediction of optimal β-lactam dosing regimens for Asian patients receiving CVVH at varying Qeff. Clinical validation is warranted.

Key Challenges in Providing Effective Antibiotic Therapy for Critically Ill Patients with Bacterial Sepsis and Septic Shock

Early initiation of effective antibiotic therapy is vitally important for saving the lives of critically ill patients with sepsis or septic shock. The susceptibility of the infecting pathogen and the ability of the selected dosage regimen to safely achieve the required antibiotic exposure need to be carefully considered to achieve a high probability of a successful outcome. Critically ill patients commonly experience substantial pathophysiological changes that impact the functions of various organs, including the kidneys. Many antibiotics are predominantly renally eliminated and thus renal function is a major determinant of the regimen needed to achieve the required antibiotic exposure. However, currently, there is a paucity of guidelines to inform antibiotic dosing in critically ill patients, including those with sepsis or septic shock. This paper briefly reviews methods that are commonly used in critically ill patients to provide a measure of renal function, and approaches that describe the relationship between the exposure to an antibiotic and its antibacterial effects. Two common conditions that very substantially complicate the use of antibiotics in critically ill patients with sepsis, unstable renal function, and augmented renal clearance, are considered in detail and their potential therapeutic implications are explored. Suggestions are provided on how treatment of bacterial infections in critically ill patients with sepsis might be improved. Of high potential are model-informed approaches that aim to individualize initial treatment regimens based on patient and bacterial characteristics, with refinement of regimens during treatment in response to monitoring antibiotic concentrations, responsive measures of renal function, and other important clinical data.

Population Pharmacokinetic Modeling and Pharmacodynamic Target Attainment Simulation of Piperacillin/Tazobactam for Dosing Optimization in Late Elderly Patients with Pneumonia

The aim of this study was to develop a population pharmacokinetic model for piperacillin (PIPC)/tazobactam (TAZ) in late elderly patients with pneumonia and to optimize the administration planning by applying pharmacokinetic/pharmacodynamic (PK/PD) criteria. PIPC/TAZ (total dose of 2.25 or 4.5 g) was infused intravenously three times daily to Japanese patients over 75 years old. The plasma concentrations of PIPC and TAZ were determined using high-performance liquid chromatography and modeled using the NONMEM program. PK/PD analysis with a random simulation was conducted using the final population PK model to estimate the probability of target attainment (PTA) profiles for various PIPC/TAZ-regimen–minimum-inhibitory-concentration (MIC) combinations. The PTAs for PIPC and TAZ were determined as the fraction that achieved at least 50% free time > MIC and area under the free-plasma-concentration–time curve over 24 h ≥ 96 μg h/mL, respectively. A total of 18 cases, the mean age of which was 86.5 ± 6.0 (75–101) years, were investigated. The plasma-concentration–time profiles of PIPC and TAZ were characterized by a two-compartment model. The parameter estimates for the final model, namely the total clearance, central distribution volume, peripheral distribution volume, and intercompartmental clearance, were 4.58 + 0.061 × (CL_cr − 37.4) L/h, 5.39 L, 6.96 L, and 20.7 L/h for PIPC, and 5.00 + 0.059 × (CL_cr − 37.4) L/h, 6.29 L, 7.73 L, and 24.0 L/h for TAZ, respectively, where CL_cr is the creatinine clearance. PK/PD analysis using the final model showed that in drug-resistant strains with a MIC > 8 μg/mL, 4.5 g of PIPC/TAZ every 6 h was required, even for the patients with a CL_cr of 50–60 mL/min. The population PK model developed in this study, together with MIC value, can be useful for optimizing the PIPC/TAZ dosage in the over-75-year-old patients, when they are administered PIPC/TAZ. Therefore, the findings of present study may contribute to improving the efficacy and safety of the administration of PIPC/TAZ therapy in late elderly patients with pneumonia.

Population pharmacokinetics and pharmacodynamics of piperacillin in critically ill patients during the early phase of sepsis

This study aimed to characterize the population pharmacokinetics (PKs) of piperacillin and investigate probability of target attainment (PTA) and cumulative fraction of response (CFR) of various dosage regimens in critically ill patients during the early phase of sepsis. Forty-eight patients treated with piperacillin/tazobactam were recruited. Five blood samples were drawn before and during 0-0.5, 0.5-2, 2-4 and 4-6 or 8 h after administration. Population PKs was analyzed using NONMEM^®. The PTA of 90%fT_>MIC target and CFR were determined by Monte Carlo simulation. The two compartment model best described the data. Piperacillin clearance (CL) was 5.37 L/h, central volume of distribution (V₁) was 9.35 L, and peripheral volume of distribution was 7.77 L. Creatinine clearance (CL_Cr) and mean arterial pressure had a significant effect on CL while adjusted body weight had a significant impact on V₁. Subtherapeutic concentrations can occur during the early phase of sepsis in critically ill patients with normal renal function. The usual dosage regimen, 4 g of piperacillin infused over 0.5 h every 6 h, could not achieve the target for susceptible organisms with MIC 16 mg/L in patients with CL_Cr ≥ 60 mL/min. Our proposed regimen for the patients with CL_Cr 60-120 mL/min was an extended 2 h infusion of 4 g of piperacillin every 6 h. Most regimens provided CFR ≥ 90% for the E. coli infection while there was no dosage regimen achieved a CFR of 90% for the P. aeruginosa infection.

Scaling beta-lactam antimicrobial pharmacokinetics from early life to old age

AIMS

Beta-lactam dose optimization in critical care is a current priority. We aimed to review the pharmacokinetics (PK) of three commonly used beta-lactams (amoxicillin ± clavulanate, piperacillin-tazobactam and meropenem) to compare PK parameters reported in critically and noncritically ill neonates, children and adults, and to investigate whether allometric and maturation scaling principles could be applied to describe changes in PK parameters through life.

METHODS

A systematic review of PK studies of the three drugs was undertaken using MEDLINE and EMBASE. PK parameters and summary statistics were extracted and scaled using allometric principles to 70 kg individual for comparison. Pooled data were used to model clearance maturation and decline using a sigmoidal (Hill) function.

RESULTS

A total of 130 papers were identified. Age ranged from 29 weeks to 82 years and weight from 0.9-200 kg. PK parameters from critically ill populations were reported with wider confidence intervals than those in healthy volunteers, indicating greater PK variability in critical illness. The standard allometric size and sigmoidal maturation model adequately described increasing clearance in neonates, and a sigmoidal model was also used to describe decline in older age. Adult weight-adjusted clearance was achieved at approximately 2 years postmenstrual age. Changes in volume of distribution were well described by the standard allometric model, although amoxicillin data suggested a relatively higher volume of distribution in neonates.

CONCLUSIONS

Critical illness is associated with greater PK variability than in healthy volunteers. The maturation models presented will be useful for optimizing beta-lactam dosing, although a prospective, age-inclusive study is warranted for external validation.

Population Pharmacokinetic Analysis of Meropenem After Intravenous Infusion in Korean Patients With Acute Infections

PURPOSE

The aim of this study was to investigate the population pharmacokinetic (PK) profile of meropenem in Korean patients with acute infections.

METHODS

The study included 37 patients with a creatinine clearance ≤50 or >50 mL/min who received a 500- or 1000-mg dose of meropenem, respectively, infused intravenously over 1 hour every 8 hours. Blood samples were collected before and at 1, 1.5, and 5 hours after the start of the fourth infusion. The population PK analysis was conducted by using nonlinear mixed effect modeling software (NONMEM). Monte-Carlo simulations were performed to identify optimal dosing regimens.

FINDINGS

Thirty-seven subjects completed the study. Meropenem PK variables were well described by using a one-compartment model. The typical values (relative SE) for weight-normalized clearance (CL) and V_d were 0.266 L/h/kg (12.29%) and 0.489 L/kg (11.01%), respectively. Meropenem CL was significantly influenced by the serum creatinine level, which explained 11% of the interindividual CK variability. The proposed equation to estimate meropenem CL in Korean patients was as follows: CL (L/h) = 0.266 × weight × [serum creatinine/0.74]^-1.017_. The simulation results indicate that the current meropenem dosing regimen may be suboptimal in patients infected with normal or augmented renal function.

IMPLICATIONS

Prolonged infusions of meropenem over at least 2 hours should be considered, especially in patients with augmented renal function and those infected with pathogens for which the minimum inhibitory meropenem concentration is >1 μg/mL. Our results suggest an individualized meropenem dosing regimen for patients with abnormal renal function and those infected with pathogens with decreased in vitro susceptibility.