Population Pharmacokinetics of Doripenem in Critically Ill Patients with Sepsis in a Malaysian Intensive Care Unit

Population pharmacokinetic analysis of doripenem for Japanese patients in intensive care unit

We aimed to construct a novel population pharmacokinetics (PPK) model of doripenem (DRPM) for Japanese patients in intensive care unit, incorporating the clearance of DRPM by continuous renal replacement therapy (CRRT). Twenty-one patients treated with DRPM (0.25 or 0.5 g) by intravenous infusion over 1 h were included in the study. Nine of the 21 patients were receiving CRRT. Plasma samples were obtained before and 1, 2, 4, 6 and 8 h after the first DRPM administration. PPK analysis was conducted by nonlinear mixed effects modeling using a two-compartment model. Total clearance (CLtotal) in the model was divided into CRRT clearance (CLCRRT) and body clearance (CLbody). The final model was: CLtotal (L h-1) = CLbody(non-CRRT) = 3.65 × (Ccr/62.25)0.64 in the absence of CRRT, or = CLbody(CRRT) + CLCRRT = 2.49 × (Ccr/52.75)0.42 + CLCRRT in the presence of CRRT; CLCRRT = QE × 0.919 (0.919 represents non-protein binding rate of DRPM); V1 (L) = 10.04; V2 (L) = 8.13; and Q (L h-1) = 3.53. Using this model, CLtotal was lower and the distribution volumes (V1 and V2) tended to be higher compared to previous reports. Also, Ccr was selected as a significant covariate for CLbody. Furthermore, the contribution rate of CLCRRT to CLtotal was 30-40%, suggesting the importance of drug removal by CRRT. The population analysis model used in this study is a useful tool for planning DRPM regimen and administration. Our novel model may contribute greatly to proper use of DRPM in patients requiring intensive care.

What Are the Current Approaches to Optimising Antimicrobial Dosing in the Intensive Care Unit?

Antimicrobial dosing in the intensive care unit (ICU) can be problematic due to various challenges including unique physiological changes observed in critically ill patients and the presence of pathogens with reduced susceptibility. These challenges result in reduced likelihood of standard antimicrobial dosing regimens achieving target exposures associated with optimal patient outcomes. Therefore, the aim of this review is to explore the various methods for optimisation of antimicrobial dosing in ICU patients. Dosing nomograms developed from pharmacokinetic/statistical models and therapeutic drug monitoring are commonly used. However, recent advances in mathematical and statistical modelling have resulted in the development of novel dosing software that utilise Bayesian forecasting and/or artificial intelligence. These programs utilise therapeutic drug monitoring results to further personalise antimicrobial therapy based on each patient’s clinical characteristics. Studies quantifying the clinical and cost benefits associated with dosing software are required before widespread use as a point-of-care system can be justified.

Pharmacokinetic variability of beta-lactams in critically ill patients: A narrative review

The use of antibacterial drugs is very common in critically ill patients and beta-lactam agents are widely used in this context. Critically ill patients show several characteristics (e.g., sepsis, renal impairment or conversely augmented renal clearance, renal replacement therapy) that may alter beta-lactam pharmacokinetics (PK) in comparison with non-critically ill patients. This narrative literature review aims to identify recent studies quantifying the variability of beta-lactams volume of distribution and clearance and to determine its main determinants. Seventy studies published between 2000 and 2018 were retained. Data on volume of distribution and clearance variability were reported for 5 penicillins, 3 beta-lactamase inhibitors, 6 cephalosporins and 4 carbapenems. Data confirm specific changes in PK parameters and important variability of beta-lactam PK in critically ill patients. Renal function, body weight and use of renal replacement therapy are the principal factors influencing PK parameters described in this population. Few studies have directly compared beta-lactam PK in critically ill versus non-critically ill patients. Conclusions are also limited by small study size and sparse PK data in several studies. These results suggest approaches to assess this PK variability in clinical practice. Beta-lactam therapeutic drug monitoring seems to be the best way to deal with this issue.

Pharmacokinetics of Doripenem in Healthy Koreans and Monte Carlo Simulations to Explore Optimal Dosage Regimens in Patients With Normal and Enhanced Renal Function

Supplemental Digital Content is Available in the Text.

Background:

Dose adjustment is often required in patients with normal or enhanced renal function. The aim of this study is to investigate the pharmacokinetic (PK) properties of doripenem and explore optimal dosing regimens in patients with normal or enhanced renal function according to various minimum inhibitory concentrations (MICs).

Methods:

The authors conducted a clinical trial and analyzed PK samples in 11 healthy Korean subjects applying noncompartmental analysis and a population approach. The population PK parameter estimates were used in Monte Carlo simulations to explore optimal dosing regimens for a probability of target attainment of 90% at 40% fT_MIC (free drug concentrations above MIC).

Results:

The time course of doripenem concentrations was well described by a 2-compartment model. The population typical values of clearance and steady-state volume were 22.9 L/h and 19.1 L, respectively, and were consistent with our noncompartmental analysis results. When the MIC was greater than 1 mcg/mL, at least increasing the dose or prolonging the infusion time was essential in patients with normal or enhanced renal function.

Conclusions:

These results suggest that dosage adjustment such as increasing the dose or lengthening the infusion time should be considered in patients with normal or enhanced renal function.

Pharmacokinetic and Pharmacodynamic Analysis of Ceftazidime/Avibactam in Critically Ill Patients

BACKGROUND

The pharmacokinetics, especially the volume of distribution (Vd), of ß-lactam antibiotics can be altered in critically ill patients. This can lead to decreased serum concentrations and a reduction in clinical cures. Ceftazidime/avibactam (CZA) is a new antimicrobial agent utilized in critically ill patients although its pharmacokinetics has not been well defined in these patients.

PATIENTS AND METHODS

In this study, the serum concentrations of CZA from adult patients treated in an intensive care unit (ICU) with standard dosing regimens were measured and both pharmacokinetic and pharmacodynamic parameters were computed. The pharmacodynamic analyses included Monte Carlo simulations to determine the probability of target attainment (PTA: free ceftazidime concentrations exceed the minimum inhibitory concentration [MIC] for 50% of the dosing interval; free avibactam concentrations exceed 1 mg/L over the dosing interval) and serum time-kill curves against multi-drug-resistant Enterobacteriaceae susceptible to CZA. Serum concentrations were measured in 10 critically ill patients at two, four, six, and eight hours after multiple doses (infused over two hours) of CZA.

RESULTS

A significant linear relation between creatinine clearance and total body clearance was identified for both ceftazidime (R = 0.91) and avibactam (R = 0.88). The mean clearance, volume of distribution, and half-life for ceftazidime were 6.1 ± 3.8 L/h, 35 ± 10.5 L, and 4.8 ± 2.15 h, respectively. For avibactam, these values were 11.1 ± 6.8 L/h, 50.8 ± 14.3 L, and 4.1 ± 2.1 h, respectively. Ceftazidime/avibactam achieved optimal PTA for bacteria with MICs of 16 mg/L or less. Furthermore, time-kill experiments revealed that serum concentrations of CZA, at each collection time, exhibited bactericidal (≥ 3 log₁₀ CFU/mL reduction) activity against each of the study isolates.

CONCLUSION

In conclusion, our study results suggest that the current dosing regimens of CZA can provide effective antimicrobial activity in ICU patients against CZA-susceptible (MIC ≤8 mg/L) isolates.

Population pharmacokinetics of intravenous paracetamol in critically ill patients with traumatic brain injury

PURPOSE

High-dose paracetamol (6 g/day) is a low-cost intervention that may prevent pyrexia. The purpose of this study was to describe the pharmacokinetics of high-dose intravenous paracetamol, in patients with traumatic brain injury (TBI).

MATERIALS AND METHODS

A clinical pharmacokinetic study in adult patients with TBI was performed as a sub-study to a prospective, phase 2B, randomized placebo-controlled study (PARITY). Patients received 1 g of intravenous paracetamol or 0.9% sodium chloride every 4 h for 72 h.

RESULTS

All patients were included in the pharmacokinetic sub-study. The mean age, weight and area under the concentration-time curve for the sampled dosing interval were 34.5 yr, 82.3 kg and 39.9 ± 19.8 mg.h/L, respectively. The concentrations observed in the study patients were well below the threshold of toxicity and there was no evidence of accumulation of paracetamol. Paracetamol clearance was found to be high and variable (25.7 L.h^-1, coefficient of variation (CV) 40.9%), and a wide range of volume of distribution observed (27.6 L, CV 30.6%). A relationship between lower Glasgow coma scores and higher clearance of paracetamol was observed.

CONCLUSION

Due to altered pharmacokinetics, patients experiencing severe TBI may require a higher dose of paracetamol to achieve drug exposure that results in preventing pyrexia.

Pharmacokinetic/Pharmacodynamic Analysis for Doripenem Regimens in Intensive Care Unit Patient

Doripenem (DRPM) is a broad-spectrum antibacterial agent often used as empirical therapy for critically ill patients, although there is a lack of studies validating the recommended dosage regimen for patients admitted to intensive care unit (ICU), based on pharmacokinetic (PK)/pharmacodynamic (PD) index. In this study, we estimated the free time above minimum inhibitory concentration (fT>MIC (%)) of DRPM using population PK analysis of 12 patients in ICU, and evaluated the validity of the dosage regimen stratified by creatinine clearance. Using a 2-compartment population PK model reported previously, the mean total clearance or distribution volume of DRPM estimated by Bayesian estimation was significantly lower or higher than that of based on population PK model. The estimated fT>MIC (%) of the recommended standard (normal renal function: 0.5 g every 8 h, moderate: 0.25 g every 8 h, severe renal impairment: 0.25 g every 12 h) and higher doses (normal: 1.0 g every 8 h, moderate: 0.5 g every 8 h, severe: 0.25 g every 8 h) against MICs of 0.5, 1 and 2 µg/mL exceeded 40% in all patients. When stratified by creatinine clearance, the PK/PD breakpoints estimated by Monte Carlo simulation in three grades of renal function tended to be higher than the previously reported PK/PD breakpoints for patients with urinary tract infection, an infection of lesser severity than ICU patients. These results suggest that the dosage regimen stratified by renal function derived from Japanese package insert may be sufficient to achieve effective treatment in ICU patients.

Antibiotic dosing for multidrug-resistant pathogen pneumonia

PURPOSE OF REVIEW

Nosocomial pneumonia caused by multidrug-resistant pathogens is increasing in the ICU, and these infections are negatively associated with patient outcomes. Optimization of antibiotic dosing has been suggested as a key intervention to improve clinical outcomes in patients with nosocomial pneumonia. This review describes the recent pharmacokinetic/pharmacodynamic data relevant to antibiotic dosing for nosocomial pneumonia caused by multidrug-resistant pathogens.

RECENT FINDINGS

Optimal antibiotic treatment is challenging in critically ill patients with nosocomial pneumonia; most dosing guidelines do not consider the altered physiology and illness severity associated with severe lung infections. Antibiotic dosing can be guided by plasma drug concentrations, which do not reflect the concentrations at the site of infection. The application of aggressive dosing regimens, in accordance to the antibiotic's pharmacokinetic/pharmacodynamic characteristics, may be required to ensure rapid and effective drug exposure in infected lung tissues.

SUMMARY

Conventional antibiotic dosing increases the likelihood of therapeutic failure in critically ill patients with nosocomial pneumonia. Alternative dosing strategies, which exploit the pharmacokinetic/pharmacodynamic properties of an antibiotic, should be strongly considered to ensure optimal antibiotic exposure and better therapeutic outcomes in these patients.

Aminoglycoside Concentrations Required for Synergy with Carbapenems against Pseudomonas aeruginosa Determined via Mechanistic Studies and Modeling

This study aimed to systematically identify the aminoglycoside concentrations required for synergy with a carbapenem and characterize the permeabilizing effect of aminoglycosides on the outer membrane of Pseudomonas aeruginosa Monotherapies and combinations of four aminoglycosides and three carbapenems were studied for activity against P. aeruginosa strain AH298-GFP in 48-h static-concentration time-kill studies (SCTK) (inoculum: 10^7.6 CFU/ml). The outer membrane-permeabilizing effect of tobramycin alone and in combination with imipenem was characterized via electron microscopy, confocal imaging, and the nitrocefin assay. A mechanism-based model (MBM) was developed to simultaneously describe the time course of bacterial killing and prevention of regrowth by imipenem combined with each of the four aminoglycosides. Notably, 0.25 mg/liter of tobramycin, which was inactive in monotherapy, achieved synergy (i.e., ≥2-log₁₀ more killing than the most active monotherapy at 24 h) combined with imipenem. Electron micrographs, confocal image analyses, and the nitrocefin uptake data showed distinct outer membrane damage by tobramycin, which was more extensive for the combination with imipenem. The MBM indicated that aminoglycosides enhanced the imipenem target site concentration up to 4.27-fold. Tobramycin was the most potent aminoglycoside to permeabilize the outer membrane; tobramycin (0.216 mg/liter), gentamicin (0.739 mg/liter), amikacin (1.70 mg/liter), or streptomycin (5.19 mg/liter) was required for half-maximal permeabilization. In summary, our SCTK, mechanistic studies and MBM indicated that tobramycin was highly synergistic and displayed the maximum outer membrane disruption potential among the tested aminoglycosides. These findings support the optimization of highly promising antibiotic combination dosage regimens for critically ill patients.

Population Pharmacokinetic Analysis of Doripenem after Intravenous Infusion in Korean Patients with Acute Infections

We investigated the population pharmacokinetics (PK) of doripenem in Korean patients with acute infections and determined an appropriate dosing regimen using a Monte Carlo simulation for predicting pharmacodynamics (PD). Patients (n = 37) with a creatinine clearance (CL_CR) of 20 to 50 ml/min or >50 ml/min who received a 250-mg or 500-mg dose of doripenem over the course of 1 h every 8 h, respectively, were included in this study. Blood samples were taken predosing and 0 h, 0.5 h, and 4 to 6 h after the fourth infusion. A nonlinear mixed-effect modeling tool was used for the PK analysis and pharmacodynamic simulation; doripenem PK were well described by a one-compartment model. The population mean values of the body weight (WT)-normalized clearance (CL/WT) and the body weight-normalized volume of distribution (V/WT) were 0.109 liter/h/kg of body weight (relative standard error, 9.197%) and 0.280 liter/kg (relative standard error, 9.56%), respectively. Doripenem CL was significantly influenced by CL_CR The proposed equation to estimate doripenem CL in Korean patients was CL/WT = 0.109 × WT × (CL_CR/57)^0.688, where CL/WT is in liters per hour per kilogram. CL in Korean patients was expected to be lower than that in Caucasian patients, regardless of renal function. The Monte Carlo simulation showed that 90% attainment of target PK/PD magnitudes could be achieved with the usual dosing regimens when the MIC was ≤1 mg/liter. However, prolonged infusions (4 h) should be considered, especially when patients have augmented renal function and for patients infected with pathogens with a high MIC. Our results provide an individualized doripenem dosing regimen for patients with various renal functions and for patients infected with bacteria with decreased susceptibility.