Pharmacokinetics of linezolid in septic patients with and without extended dialysis

External evaluation of the predictive performance of published population pharmacokinetic models of linezolid in adult patients

OBJECTIVES

Several linezolid population pharmacokinetic (popPK) models have been established to facilitate optimal therapy; however, their extrapolated predictive performance to other clinical sites is unknown. This study aimed to externally evaluate the predictive performance of published pharmacokinetic models of linezolid in adult patients.

METHODS

For the evaluation dataset, 150 samples were collected from 70 adult patients (72.9% of which were critically ill) treated with linezolid at our center. Twenty-five published popPK models were identified from PubMed and Embase. Model predictability was evaluated using prediction-based, simulation-based, and Bayesian forecasting-based approaches to assess model predictability.

RESULTS

Prediction-based diagnostics found that the prediction error within ±30% (F30) was less than 40% in all models, indicating unsatisfactory predictability. The simulation-based prediction- and variability-corrected visual predictive check and normalized prediction distribution error test indicated large discrepancies between the observations and simulations in most of the models. Bayesian forecasting with one or two prior observations significantly improved the models' predictive performance.

CONCLUSION

The published linezolid popPK models showed insufficient predictive ability. Therefore, their sole use is not recommended, and incorporating therapeutic drug monitoring of linezolid in clinical applications is necessary.

Antimicrobial pharmacokinetics and dosing in critically ill adults receiving prolonged intermittent renal replacement therapy: A systematic review

Prolonged intermittent renal replacement therapy (PIRRT) is gaining popularity as a renal replacement modality in intensive care units, but there is a relative lack of guidance regarding antimicrobial clearance and dosing when compared with other modalities. The objectives of this systematic review were to: (1) identify and describe the pharmacokinetics (PK) of relevant antimicrobials used in critically ill adults receiving PIRRT, (2) evaluate the quality of evidence supporting these data, and (3) propose dosing recommendations based on the synthesis of these data. A search strategy for multiple databases was designed and executed to identify relevant published evidence describing the PK of antimicrobials used in critically ill adults receiving PIRRT. Quality assessment, evaluation of reporting, and relevant data extraction were conducted in duplicate. Synthesis of PK/pharmacodynamic (PD) outcomes, dosing recommendations from study authors, and physicochemical properties of included antibiotics were assessed by investigators in addition to the quality of evidence to develop dosing recommendations. Thirty-nine studies enrolling 452 patients met criteria for inclusion and provided PK and/or PD data for 20 antimicrobials in critically ill adults receiving PIRRT. Nineteen studies describe both PK and PD outcomes. Vancomycin (12 studies, 171 patients), meropenem (7 studies, 84 patients), and piperacillin/tazobactam (5 studies, 56 patients) were the most frequent antimicrobials encountered. The quality of evidence was deemed strong for 7/20 antimicrobials, and strong dosing recommendations were determined for 9/20 antimicrobials. This systematic review updates and addresses issues of quality in previous systematic reviews on this topic. Despite an overall low quality of evidence, strong recommendations were able to be made for almost half of the identified antimicrobials. Knowledge gaps persist for many antimicrobials, and higher quality studies (i.e., population PK studies with assessment of PD target attainment) are needed to address these gaps.

24/7 Therapeutic Drug Monitoring of Beta-Lactam Antibiotics with CLAM-2000

BACKGROUND

The aim of this study was to evaluate the CLAM-2000 automated preanalytical sample preparation module with integrated liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) as a method for 24/7 therapeutic drug monitoring (TDM) of beta-lactam antibiotics in routine clinical diagnostics.

METHODS

Method validation was performed using quality control samples. Method comparison was performed with routine samples from patients treated with beta-lactam antibiotics.

RESULTS

The determination of piperacillin, meropenem, ceftazidime, flucloxacillin, and cefotaxime was performed using D5-piperacillin and D6-meropenem as internal standards. The linearity of the method was within the therapeutic range of beta-lactam antibiotics. The imprecision and accuracy data obtained from quality control samples were within 15%, and the imprecision of patient samples on the instrument was less than the 5% coefficient of variation (CV). Internal standards stored in the instrument at 9 °C for at least one week were stable, which facilitated reagent use and storage.

CONCLUSION

The CLAM-2000 (Shimadzu, Kyoto, Japan) provides reproducible results as an established routine instrument and is a useful tool for 24/7 TDM of beta-lactam antibiotics in routine clinical diagnostics.

Linezolid dosing in critically ill patients undergoing various modalities of renal replacement therapy: a pooled population pharmacokinetic analysis

The altered pharmacokinetics (PK) of linezolid are pronounced in critically ill patients undergoing different modalities of renal replacement therapy (RRT). This study aimed to provide a pooled population PK analysis of linezolid in patients undergoing RRT, and to evaluate the pharmacodynamic target attainment of linezolid standard dosing (600 mg q12h). In total, 414 pooled linezolid concentration observations from 69 patients undergoing intermittent haemodialysis (IHD), sustained low-efficiency dialysis (SLED) or continuous RRT were used to develop the population PK model. The probability of target attainment (PTA) for the efficacy markers of 85% T>minimum inhibitory concentration (MIC) and area under the concentration-time curve (AUC)/MIC >100 was evaluated, and the risk of toxicity was estimated based on Cmin ≥10 mg/L. Linezolid concentration data were described adequately by a two-compartment model. Renal function and body weight were identified as significant modifiers for endogenous clearance of linezolid. Simulations demonstrated that the PTA of 85% T>MIC and AUC/MIC>100 was unacceptably low (0-58.6%, MIC ≥1 mg/L) in RRT patients with preserved renal function, while desirable 85% T>MIC attainment (≥ 90%, MIC ≤2 mg/L) was achieved in anuric RRT patients. The predicted risk of toxicity was negligible (<1.0%) in patients with preserved renal function (regardless of RRT modality), while the probability of reaching Cmin ≥10 mg/L was high (17.9-20.9%) for the anuric patient population undergoing IHD or SLED. In conclusion, standard linezolid dosing is adequate for anuric RRT patients with MIC ≤2 mg/L.

Acute-on-chronic liver failure alters linezolid pharmacokinetics in critically ill patients with continuous hemodialysis: an observational study

BACKGROUND

In acute-on-chronic liver failure (ACLF), adequate antibiotic dosing is challenging due to changes of drug distribution and elimination. We studied the pharmacokinetics of linezolid in critically ill patients with ACLF during continuous renal replacement therapy compared to patients without concomitant liver failure (NLF).

METHODS

In this prospective cohort study, patients received linezolid 600 mg bid. Linezolid serum samples were analyzed by high-performance liquid chromatography. Population pharmacokinetic modelling was performed followed by Monte-Carlo simulations of 150 mg bid, 300 mg bid, 450 mg bid, 600 mg bid, and 900 mg bid to assess trough concentration target attainment of 2-7 mg/L.

RESULTS

Eighteen patients were included in this study with nine suffering from ACLF. Linezolid body clearance was lower in the ACLF group with mean (standard deviation) 1.54 (0.52) L/h versus 6.26 (2.43) L/h for NLF, P < 0.001. A trough concentration of 2-7 mg/L was reached with the standard dose of 600 mg bid in the NLF group in 47%, with 42% being underexposed and 11% overexposed versus 20% in the ACLF group with 77% overexposed and 3% underexposed. The highest probability of target exposure was attained with 600 mg bid in the NLF group and 150 mg bid in the ACLF group with 53%.

CONCLUSION

Linezolid body clearance in ACLF was markedly lower than in NLF. Given the overall high variability, therapeutic drug monitoring (TDM) with dose adjustments seems required to optimize target attainment. Until TDM results are available, a dose reduction may be considered in ACLF patients to prevent overexposure.

Safety of linezolid in patients with decreased renal function and trough monitoring: a systematic review and meta-analysis

BACKGROUND

Linezolid causes hematological toxicity, mostly thrombocytopenia, which leads to treatment discontinuation and failure. Recent studies revealed that during linezolid therapy, the incidence of treatment-related hematological toxicity is significantly higher in patients with decreased renal function (DRF) than in those with normal renal function. Linezolid monitoring is necessary due to the high frequency of hematological toxicity in patients with DRF and the relationship between blood concentration and safety. We performed a systematic review and meta-analysis to evaluate the safety correlation between DRF and trough monitoring.

METHODS

Articles published before June 24, 2022, on MEDLINE, Web of Sciences, Cochrane Register of Controlled Trials, and ClinicalTrials.gov were systematically analyzed. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated using the Mantel-Haenszel method and the variable effects model.

RESULTS

The incidence of hematological toxicity was significantly higher in patients with DRF than in those without DRF (OR = 2.37; p < 0.001). Subgroup analysis, performed according to hematotoxicity classification, including thrombocytopenia, anemia, and pancytopenia, revealed a significantly higher incidence of thrombocytopenia (OR = 2.45; p < 0.001) and anemia (OR = 2.31; p = 0.006) in patients with DRF than in those without; pancytopenia (OR = 1.41; p = 0.80) incidences were not significantly higher. Based on a systematic review, linezolid trough concentrations > 6-7 μg/mL may be associated with an increased incidence of thrombocytopenia. However, no confidential threshold values for the development of thrombocytopenia were found in the area under the concentration curve values for children or adults.

CONCLUSION

We observed a high frequency of hematological toxicity during linezolid therapy in patients with DRF. To ensure safety, linezolid trough concentrations should be ≤6-7 μg/mL.

A Review of Population Pharmacokinetic Analyses of Linezolid

In recent years, many studies on population pharmacokinetics of linezolid have been conducted. This comprehensive review aimed to summarize population pharmacokinetic models of linezolid, by focusing on dosage optimization to maximize the probability of attaining a certain pharmacokinetic-pharmacodynamic parameter in special populations. We searched the PubMed and EMBASE databases for population pharmacokinetic analyses of linezolid using a parametric non-linear mixed-effect approach, including both observational and prospective trials. Of the 32 studies, 26 were performed in adults, four in children, and one in both adults and children. High between-subject variability was determined in the majority of the models, which was in line with the variability of linezolid concentrations previously detected in observational studies. Some studies found that patients with renal impairment, hepatic failure, advanced age, or low body weight had higher exposure and adverse reactions rates. In contrast, lower concentrations and therapeutic failure were associated with obese patients, young patients, and patients who had undergone renal replacement techniques. In critically ill patients, the inter-individual and intra-individual variability was even greater, suggesting that this population is at an even higher risk of underexposure and overexposure. Therapeutic drug monitoring may be warranted in a large proportion of patients given that the Monte Carlo simulations demonstrated that the one-size-fits-all labeled dosing of 600 mg every 12 h could lead to toxicity or therapeutic failure for high values of the minimum inhibitory concentration of the target pathogen. Further research on covariates, including renal function, hepatic function, and drug–drug interactions related to P-glycoprotein could help to explain variability and improve linezolid dosing regimens.

Therapeutic Drug Monitoring of Antibiotic Drugs in Patients Receiving Continuous Renal Replacement Therapy or Intermittent Hemodialysis: A Critical Review

PURPOSE

Antibiotics are frequently used in patients receiving intermittent or continuous renal replacement therapy (RRT). Continuous renal replacement may alter the pharmacokinetics (PK) and the ability to achieve PK/pharmacodynamic (PD) targets. Therapeutic drug monitoring (TDM) could help evaluate drug exposure and guide antibiotic dosage adjustment. The present review describes recent TDM data on antibiotic exposure and PK/PD target attainment (TA) in patients receiving intermittent or continuous RRT, proposing practical guidelines for performing TDM.

METHODS

Studies on antibiotic TDM performed in patients receiving intermittent or continuous RRT published between 2000 and 2020 were searched and assessed. The authors focused on studies that reported data on PK/PD TA. TDM recommendations were based on clinically relevant PK/PD relationships and previously published guidelines.

RESULTS

In total, 2383 reports were retrieved. After excluding nonrelevant publications, 139 articles were selected. Overall, 107 studies reported PK/PD TA for 24 agents. Data were available for various intermittent and continuous RRT techniques. The study design, TDM practice, and definition of PK/PD targets were inconsistent across studies. Drug exposure and TA rates were highly variable. TDM seems to be necessary to control drug exposure in patients receiving intermittent and continuous RRT techniques, especially for antibiotics with narrow therapeutic margins and in critically ill patients. Practical recommendations can provide insights on relevant PK/PD targets, sampling, and timing of TDM for various antibiotic classes.

CONCLUSIONS

Highly variable antibiotic exposure and TA have been reported in patients receiving intermittent or continuous RRT. TDM for aminoglycosides, beta-lactams, glycopeptides, linezolid, and colistin is recommended in patients receiving RRT and suggested for daptomycin, fluoroquinolones, and tigecycline in critically ill patients on RRT.

Liver function, quantified by the LiMAx test, as a predictor for the clinical outcome of critically ill patients treated with linezolid

BACKGROUND

Critically ill patients commonly suffer from infections that require antimicrobial therapy. In previous studies, liver dysfunction was shown to have an essential impact on the dose selection in these patients. This pilot study aims to assess the influence of liver dysfunction, measured by the novel LiMAx test, on clinical outcomes in critically ill patients treated with linezolid.

METHODS

Twenty-nine critically ill patients were included and treated with linezolid. Indications for linezolid therapy were secondary or tertiary peritonitis (46.7%), bloodstream infection (6.7%) and 46.7% were other infections with gram-positive bacteria. Linezolid Cmin, maximal liver function capacity (LiMAx test) and plasma samples were collected while linezolid therapy was in a steady-state condition. Furthermore, potential factors for the clinical outcome were investigated using logistic regression analysis. Clinical cure was defined as the resolution or significant improvement of clinical symptoms without using additional antibiotic therapy or intervention.

RESULTS

Cured patients presented lower median linezolid Cmin yet a significantly higher mean LiMAx-value compared to the clinical failure group (1.9 mg/L vs. 5.1 mg/L) (349 μg/kg/h vs. 131 μg/kg/h). In the logistic regression model, LiMAx < 178 μg/kg/h was the only independent predictor of clinical failure with a sensitivity of 77% and specificity of 93%.

CONCLUSIONS

The LiMAx test predicts clinical failure more precisely than linezolid trough levels in critically ill surgical patients. Therefore liver failure may have a stronger impact on the outcome of critically ill surgical patients than low linezolid Cmin. While linezolid Cmin failed to predict patient's outcome, LiMAx results were the only independent predictor of clinical failure.

In linezolid underexposure, pharmacogenetics matters: The role of CYP3A5

The exposure to linezolid is characterized by a large inter-individual variability; age, renal dysfunction and body weight explain this variability only to a limited extent and a considerable portion of it remains unexplained; therefore, we decided to investigate the role of individual genetic background focusing in particular on the risk of linezolid underexposure. 191 patients in therapy with linezolid at the standard dose of 600 mg twice daily were considered. Linezolid plasma concentration was determined at the steady state and classified as "below", "within" or "above" reference range. Genetic polymorphisms for ATP Binding Cassette Subfamily B Member 1 (ABCB1), Cytochrome P450 (CYP) enzymes CYP3A4 and CYP3A5, and Cytochrome P450 Oxidoreductase (POR) were investigated. Age significantly correlated with drug exposure, and patients CYP3A5 expressers (GA and AA) were found at high risk to be underexposed to the drug when treated at standard dose. This association was confirmed even after correction with age. No association was found with ABCB1 polymorphism. Our data suggest that CYP3A5 polymorphisms might significantly affect linezolid disposition, putting patients at higher risk to be underexposed, while P-glycoprotein polymorphism seem not to play any role.

Pharmacokinetics and Pharmacodynamics of Linezolid in Patients With Sepsis Receiving Continuous Venovenous Hemofiltration and Extended Daily Hemofiltration

BACKGROUND

This prospective study compared pharmacokinetics (PK) and pharmacodynamics (PD) of linezolid in patients with sepsis receiving continuous venovenous hemofiltration (CVVH) with patients receiving extended daily hemofiltration (EDH).

METHODS

Patients with sepsis treated with linezolid and CVVH or EDH were included. Serial blood samples were collected and linezolid concentrations measured. PKs were analyzed using Pmetrics. Monte Carlo simulations were used to evaluate PD target achievement.

RESULTS

From 20 patients, 320 blood samples were collected for PK and PD analysis. PK profiles of linezolid were best described by a 2-compartment model. PK parameters were not significantly different between EDH and CVVH groups and were associated with body weight, renal replacement therapy (RRT) duration, and sequential organ failure assessment score. Monte Carlo simulations showed poor fractional target attainment for a minimum inhibitory concentration (MIC) of 2 mg/L with standard 600 mg intravenous administration every 12 hours.

CONCLUSIONS

Patients with sepsis receiving RRT exhibited variability in PK/PD parameters for linezolid. PK parameters were not significantly different between CVVH- and EDH-treated patients. Higher probability of target attainment would be achievable at a MIC of 2 mg/L in EDH patients. Higher linezolid doses should be considered for patients on RRT to achieve adequate blood levels.

Population Pharmacokinetics and Dosage Optimization of Linezolid in Patients with Liver Dysfunction

Linezolid is the first synthetic oxazolidone agent to treat infections caused by Gram-positive pathogens. Infected patients with liver dysfunction (LD) are more likely to suffer from adverse reactions, such as thrombocytopenia, when standard-dose linezolid is used than patients with LD who did not use linezolid. Currently, pharmacokinetics data of linezolid in patients with LD are limited. This study aimed to characterize pharmacokinetics parameters of linezolid in patients with LD, identify the factors influencing the pharmacokinetics, and propose an optimal dosage regimen. We conducted a prospective study and established a population pharmacokinetics model with the Phoenix NLME software. The final model was evaluated by goodness-of-fit plots, bootstrap analysis, and prediction corrected-visual predictive check. A total of 163 concentration samples from 45 patients with LD were adequately described by a one-compartment model with first-order elimination along with prothrombin activity (PTA) and creatinine clearance as significant covariates. Linezolid clearance (CL) was 2.68 liters/h (95% confidence interval [CI], 2.34 to 3.03 liters/h); the volume of distribution (V) was 58.34 liters (95% CI, 48.00 to 68.68 liters). Model-based simulation indicated that the conventional dose was at risk for overexposure in patients with LD or severe renal dysfunction; reduced dosage (300 mg/12 h) would be appropriate to achieve safe (minimum steady-state concentration [C _min,ss] at 2 to 8 μg/ml) and effective targets (the ratio of area under the concentration-time curve from 0 to 24 h [AUC_0-24] at steady state to MIC, 80 to 100). In addition, for patients with severe LD (PTA, ≤20%), the dosage (400 mg/24 h) was sufficient at an MIC of ≤2 μg/ml. This study recommended therapeutic drug monitoring for patients with LD. (This study has been registered in the Chinese Clinical Trial Registry under no. ChiCTR1900022118.).

Principles of Drug Dosing in Sustained Low Efficiency Dialysis (SLED) and Review of Antimicrobial Dosing Literature

The use of sustained low-efficiency dialysis (SLED) as a renal replacement modality has increased in critically ill patients with both acute kidney injury (AKI) and hemodynamic instability. Unfortunately, there is a paucity of data regarding the appropriate dosing of medications for patients undergoing SLED. Dose adjustment in SLED often requires interpretation of pharmacodynamics and pharmacokinetic factors and extrapolation based on dosing recommendations from other modes of renal replacement therapy (RRT). This review summarizes published trials of antimicrobial dose adjustment in SLED and discusses pharmacokinetic considerations specific to medication dosing in SLED. Preliminary recommendation is provided on selection of appropriate dosing for medications where published literature is unavailable.

Determining therapeutic trough ranges for linezolid

Linezolid (LZD) is an oxazolidinone approved for the treatment of gram-positive infections. Therapeutic drug monitoring is increasingly used to optimize LZD dosing. The therapeutic target for LZD is to achieve an area under the concentration-time curve over 24 h divided by the MIC (AUC/MIC) > 100. In this study, we determined the trough ranges associated with this therapeutic AUC. Concentration-time profiles for 999 virtual patients were simulated using a previously published pharmacokinetic model for LZD. AUC was estimated for each virtual patient using the trapezoidal method. We determined the trough ranges that achieve the therapeutic target of AUC/MIC > 100 at different MIC values of 1, 2 and 4 μg/mL. Trough samples correlated well with LZD AUC (R² = 0.87). For trough concentration of 2–5 μg/mL, 99% had an AUC_0–24 > 100 µg⋅h⋅ml⁻¹, 23% had an AUC_0–24 > 200 µg⋅h⋅ml⁻¹ and none had an AUC_0–24 > 400 µg⋅h⋅ml⁻¹. For trough concentrations of 5–8 µg/ml, 87% of the patients had an AUC_0–24 > 200 µg⋅h⋅ml⁻¹ and none had an AUC_0–24 > 400 µg⋅h⋅ml⁻¹ To achieve the therapeutic target of an AUC/MIC > 100, it is suggested that trough ranges be set at 2–5 µg/ml if the MIC < 2 and 5–8 µg/ml if the MIC = 2; however, at an MIC of 4 µg/ml, it is difficult to achieve an AUC/MIC > 100 without increasing the risk of LZD toxicity.

A Guide to Understanding Antimicrobial Drug Dosing in Critically Ill Patients on Renal Replacement Therapy

A careful management of antimicrobials is essential in the critically ill with acute kidney injury, especially if renal replacement therapy is required. Acute kidney injury may lead per se to clinically significant modifications of drugs' pharmacokinetic parameters, and the need for renal replacement therapy represents a further variable that should be considered to avoid inappropriate antimicrobial therapy. The most important pharmacokinetic parameters, useful to determine the significance of extracorporeal removal of a given drug, are molecular weight, protein binding, and distribution volume. In many cases, the extracorporeal removal of antimicrobials can be relevant, with a consistent risk of underdosing-related treatment failure and/or potential onset of bacterial resistance. It should also be taken into account that renal replacement therapies are often not standardized in critically ill patients, and their impact on plasma drug concentrations may substantially vary in relation to membrane characteristics, treatment modality, and delivered dialysis dose. Thus, in this clinical scenario, the knowledge of the pharmacokinetic and pharmacodynamic properties of different antimicrobial classes is crucial to tailor maintenance dose and/or time interval according to clinical needs. Finally, especially for antimicrobials known for a tight therapeutic range, therapeutic drug monitoring is strongly suggested to guide dosing adjustment in complex clinical settings, such as septic patients with acute kidney injury undergoing renal replacement therapy.

Antibiotic Distribution into Cerebrospinal Fluid: Can Dosing Safely Account for Drug and Disease Factors in the Treatment of Ventriculostomy-Associated Infections?

Ventriculostomy-associated infections, or ventriculitis, in critically ill patients are associated with considerable morbidity. Efficacious antibiotic dosing for the treatment of these infections may be complicated by altered antibiotic concentrations in the cerebrospinal fluid due to variable meningeal inflammation and antibiotic properties. Therefore, doses used to treat infections with a higher degree of meningeal inflammation (such as meningitis) may often fail to achieve equivalent exposures in patients with ventriculostomy-associated infections such as ventriculitis. This paper aims to review the disease burden, infection rates, and common pathogens associated with ventriculostomy-associated infections. This review also seeks to describe the disease- and drug-related factors that influence antibiotic distribution into cerebrospinal fluid and provide a critical appraisal of current dosing of antibiotics commonly used to treat these types of infections. A Medline search of relevant articles was conducted and used to support a review of cerebrospinal fluid penetration of vancomycin, including critical appraisal of the recent paper by Beach et al. recently published in this journal. We found that in the intensive care unit, ventriculostomy-associated infections are the most common and serious complication of external ventricular drain insertion and often result in prolonged patient stay and increased healthcare costs. Reported infection rates are extremely variable (between 0 and 45%), hindered by the inherent diagnostic difficulty. Both Gram-positive and Gram-negative organisms are associated with such infections and the rise of multi-drug-resistant pathogens means that effective treatment is an ongoing challenge. Disease factors that may need to be considered are reduced meningeal inflammation and the presence of critical illness; drug factors include physiochemical properties, degree of plasma-protein binding, and affinity to active transporter proteins present in the blood-cerebrospinal fluid barrier. The relationship between cerebrospinal fluid antibiotic exposures in the setting of ventriculostomy-associated infection and clinical response has not been fully elucidated for many of the antibiotics commonly used in its treatment. More thorough and clinically relevant investigations are needed to better define blood pharmacokinetic/pharmacodynamics targets and optimal therapeutic exposures for treatment of ventriculostomy-associated infections. It is hoped that this future research will be able to provide clearer recommendations for clinicians frequently faced with dosing-related dilemmas when treating patients with these challenging infections.

Clinical Determinants of Target Non-Attainment of Linezolid in Plasma and Interstitial Space Fluid: A Pooled Population Pharmacokinetic Analysis with Focus on Critically Ill Patients

OBJECTIVES

We aimed to assess linezolid pharmacokinetics in the plasma and interstitial space fluid (ISF) of patients with sepsis, diabetic foot infections or cystic fibrosis and healthy volunteers. The impacts of joint characteristics and disease on plasma and target-site exposure were to be identified together with the benefit of dose intensification in critically ill patients.

METHODS

Rich plasma (n = 1598) and ISF concentrations in subcutaneous adipose (n = 1430) and muscle tissue (n = 1089) measured by microdialysis were pooled from three clinical trials with 51 individuals receiving 600 mg of intravenous and oral linezolid. All data were analysed simultaneously by a population approach also considering methodological aspects of microdialysis. The impact of covariates on the attainment of the pharmacokinetic/pharmacodynamic targets, AUC/MIC = 100 (area under the concentration-time curve/minimum inhibitory concentration) and fT_>MIC = 99 % (time that unbound concentrations exceed the MIC), was assessed by deterministic and Monte Carlo simulations.

RESULTS

A two-compartment pharmacokinetic model with nonlinear elimination and tissue distribution factors accounting for differences between plasma and ISF concentrations adequately predicted all measurements. Clearance (CL) was highest in septic patients (11.2 L/h vs. CL_Healthy/CL_{Cystic fibrosis}/CL_Diabetic = 7.67/6.87/6.35 L/h). Penetration into subcutaneous adipose ISF was lowest in diabetic patients (-34.9 % compared with healthy volunteers). Creatinine clearance and total body weight further impacted linezolid exposure. To achieve timely efficacious therapy, front-loaded dosing and continuous infusion seemed beneficial in septic patients.

CONCLUSIONS

Our analysis suggests that after standard linezolid doses, particularly patients with sepsis and conserved renal function are at risk of not attaining pharmacokinetic/pharmacodynamic targets and would benefit from initial dose intensification.

Population pharmacokinetics and dosing simulations of ceftazidime in critically ill patients receiving sustained low-efficiency dialysis

Objectives

To describe the population PKs of ceftazidime in critically ill patients receiving sustained low-efficiency dialysis (SLED).

Patients and methods

This study was performed in ICUs of a university hospital. We collected blood samples during three consecutive days of SLED sessions in patients receiving ceftazidime. Concentration versus time curves were analysed using a population PKs approach with Pmetrics ® . Monte Carlo simulation for the first 24 h including a 6 h SLED session was performed with the final model. The fractional target attainment against the MIC of Pseudomonas aeruginosa was executed using targets of 50 and 100% fT  >   MIC .

Results

In total, 211 blood samples of 16 critically ill patients under SLED were collected. SLED treatments were 299.3 (68.4) min in duration. A two-compartment linear population PK model was most appropriate. The mean (SD) CL of ceftazidime on SLED, and off SLED were 5.32 (3.2), 1.06 (1.0) L/h respectively. The PTA for 50% fT  >   MIC for a dose of 1 g intravenously every 8 h was 98%. Assuming a target of 100% fT  >   MIC a dose of 2 g every 12 h covers isolates with MIC ≤8 mg/L with a PTA of 96%.

Conclusion

In critically ill patients receiving SLED, ceftazidime 1 g every 8 h and ceftazidime 2 g every 12 h appear to be sufficient for achieving traditional (50% fT  >   MIC ) and aggressive PD targets (100% fT  >   MIC ) for susceptible isolates (MIC ≤8 mg/L), respectively.

Linezolid in liver failure: exploring the value of the maximal liver function capacity (LiMAx) test in a pharmacokinetic pilot study

Patients in the intensive care unit frequently require antibiotic treatment. Liver impairment poses substantial challenges for dose selection in these patients. The aim of the present pilot study was to assess the novel maximal liver function capacity (LiMAx test) in comparison with conventional liver function markers as covariates of drug clearance in liver failure using linezolid as a model drug. A total of 28 patients with different degrees of liver failure were recruited. LiMAx test as well as plasma, dialysate and urine sampling were performed under linezolid steady-state therapy (600 mg twice daily). NONMEM^® was used for a pharmacometric analysis in which the different clearance routes of linezolid were elucidated. Linezolid pharmacokinetics was highly variable in patients with liver failure. The LiMAx score displayed the strongest association with non-renal clearance (CL_non-renal) [ = 4.46∙(body weight/57.9) ^0.75∙(LiMAx/221.5)^0.388 L/h], which reduced interindividual variability in CL_non-renal from 46.6% to 33.6%, thereby being superior to other common markers of liver function (international normalised ratio, gamma-glutaryl transferase, bilirubin, thrombocytes, alanine aminotransferase, aspartate aminotransferase). For LiMAx < 100 µg/kg/h, 64% of linezolid trough concentrations were above the recommended trough concentration of 8 mg/L, indicating the necessity of therapeutic drug monitoring in these patients. This is the first pilot application of the LiMAx test in a pharmacokinetic (PK) study demonstrating its potential to explain PK variability in linezolid clearance. Further studies with a larger patient collective and further drugs are highly warranted to guide dosing in patients with severe liver impairment.

Survey of pharmacists’ antibiotic dosing recommendations for sustained low-efficiency dialysis

BACKGROUND

The use of hybrid renal replacement therapies like sustained low efficiency dialysis (SLED) is increasing in ICUs worldwide. However, pharmacokinetic studies designed to inform therapeutic antibiotic dosing in critically ill patients receiving SLED are limited. SLED operational characteristics vary across institutions. Pharmacists in institutions that utilize SLED are challenged to recommend therapeutic doses for antibiotics.

OBJECTIVE

To characterize pharmacist-recommended antibiotic regimens for SLED.

METHODS

An electronic survey was sent to pharmacist members of the American College of Clinical Pharmacy in the Nephrology or Critical Care Practice and Research Network. Dosing recommendations for a hypothetical critically ill septic patient were collected for cefepime, ceftaroline, daptomycin, levofloxacin, meropenem, and piperacillin/tazobactam. Main outcome measure Antibiotic regimens for the six antibiotics, their frequency, pharmacist’s experience with renal replacement therapies (RRT), post-graduate training, years of clinical experience, number of staffed beds in their hospital, and RRT employed in their ICUs.

RESULTS

The survey was completed by 69 clinical pharmacists who had 8.5 ± 7.5 (mean ± SD) years of experience. All pharmacists had experience dosing medications for patients receiving RRT. The most frequently recommended regimen for each antibiotic was: cefepime 1000 mg every 24 h, ceftaroline 200 mg every 12 h, daptomycin 6 mg/kg every 24 h, levofloxacin 500 mg every 24 h, meropenem 1000 mg every 12 h, and piperacillin/tazobactam 2250 mg every 8 h. Up to nine distinct regimens were recommended for each antibiotic, and the total daily dose between these regimens ranged by as much as a 12-fold. Neither pharmacist’s experience with SLED, post-graduate training, nor years of clinical experience were significantly associated with particular dosing recommendations for the antibiotics.

CONCLUSION

Pharmacists working in institutions that utilize SLED make antibiotic dosing recommendations that vary 4–12-fold depending on the drug. Published research does not provide adequate guidance to optimally dose antibiotics in patients receiving SLED. More SLED pharmacokinetic trials, real-time serum concentration monitoring and advanced pharmacokinetic modeling techniques are necessary to ensure therapeutic dosing in patients receiving SLED.

Predictors of Inadequate Linezolid Concentrations after Standard Dosing in Critically Ill Patients

Adequate linezolid blood concentrations have been shown to be associated with an improved clinical outcome. Our goal was to assess new predictors of inadequate linezolid concentrations often observed in critically ill patients. Fifty-two critically ill patients with severe infections receiving standard dosing of linezolid participated in this prospective observational study. Serum samples (median, 32 per patient) were taken on four consecutive days, and total linezolid concentrations were quantified. Covariates influencing linezolid pharmacokinetics were identified by multivariate analysis and a population pharmacokinetic model. Target attainment (area under the concentration-time curve over 12 h [AUC12]/MIC ratio of >50; MIC = 2 mg/liter) was calculated for both the study patients and a simulated independent patient group (n = 67,000). Target attainment was observed for only 36% of the population on both days 1 and 4. Independent covariates related to significant decreases of linezolid concentrations included higher weight, creatinine clearance rates, and fibrinogen and antithrombin concentrations, lower concentrations of lactate, and the presence of acute respiratory distress syndrome (ARDS). Linezolid clearance was increased in ARDS patients (by 82%) and in patients with elevated fibrinogen or decreased lactate concentrations. In simulated patients, most covariates, including fibrinogen and lactate concentrations and weight, showed quantitatively minor effects on target attainment (difference of ≤9% between the first and fourth quartiles of the respective parameters). In contrast, the presence of ARDS had the strongest influence, with only ≤6% of simulated patients reaching this target. In conclusion, the presence of ARDS was identified as a new and strong predictor of insufficient linezolid concentrations, which might cause treatment failure. Insufficient concentrations might also be a major problem in patients with combined alterations of other covariate parameters. (This study has been registered at ClinicalTrials.gov under registration number NCT01793012.).

Pharmacokinetic/pharmacodynamic evaluation of linezolid for the treatment of staphylococcal infections in critically ill patients

Several studies have demonstrated that the ideal therapeutic effect of linezolid cannot be achieved in critically ill patients with the recommended standard dosing regimen of 600 mg every 12 h (q12h). Moreover, the optimal strategy for successful treatment is still lacking. This study analysed factors influencing the efficacy of linezolid treatment and determined the target for successful treatment by logistic regression in 27 critically ill patients with staphylococcal infection who received linezolid 600 mg q12h. The results showed that only the 24-h area under the concentration-time curve to minimum inhibitory concentration (AUC24/MIC) ratio was significantly associated with staphylococcal eradication. Reaching 80% bacterial eradication required an AUC24/MIC of 120.5, defining the therapeutic target. Different dosing regimens were evaluated using Monte Carlo simulation to determine the optimal dosage strategy for linezolid. Although the probability of target attainment (PTA) was high (>99.9%) for the standard dosing regimen at MIC ≤ 1 mg/L, the PTA was almost 0 at MIC = 2 mg/L, thus the dosing regimen required adjustment. In addition, if the dosing regimen was adjusted to 600 mg every 8 h or 600 mg every 6 h, the major staphylococci (except for MRSA and MSSA) exhibited a cumulative fraction of response of >80%, showing a higher treatment success. These findings indicate that a strategy of high linezolid dosage may be needed to increase the probability of successful treatment at MIC > 1 mg/L. The role of therapeutic drug monitoring should be encouraged for optimising linezolid exposure in critically ill patients.

Therapeutic drug monitoring of anti-infective agents in critically ill patients

Initial adequate anti-infective therapy is associated with significantly improved clinical outcomes for patients with severe infections. However, in critically ill patients, several pathophysiological and/or iatrogenic factors may affect the pharmacokinetics of anti-infective agents leading to suboptimal drug exposure, in particular during the early phase of therapy. Therapeutic drug monitoring (TDM) may assist to overcome this problem. We discuss the available evidence on the use of TDM in critically ill patient populations for a number of anti-infective agents, including aminoglycosides, β-lactams, glycopeptides, antifungals and antivirals. Also, we present the available evidence on the practices of anti-infective TDM and describe the potential utility of TDM to improve treatment outcome in critically ill patients with severe infections. For aminoglycosides, glycopeptides and voriconazole, beneficial effects of TDM have been established on both drug effectiveness and potential side effects. However, for other drugs, therapeutic ranges need to be further defined to optimize treatment prescription in this setting.

Pharmacokinetics of linezolid in critically ill patients

INTRODUCTION

Linezolid is an oxazolidinone antibiotic active against Gram-positive bacteria, and is most commonly used to treat life-threatening infections in critically ill patients. The pharmacokinetics of linezolid are profoundly altered in critically ill patients, partly due to decreased function of vital organs, and partly because life-sustaining drugs and devices may change the extent of its excretion.

AREAS COVERED

This article is summarizes key changes in the pharmacokinetics of linezolid in critically ill patients. The changes summarized are clinically relevant and may serve as rationale for dosing recommendations in this particular population.

EXPERT OPINION

While absorption and penetration of linezolid to tissues are not significantly changed in critically ill patients, protein binding of linezolid is decreased, volume of distribution increased, and metabolism may be inhibited leading to non-linear kinetics of elimination; these changes are responsible for high inter-individual variability of linezolid plasma concentrations, which requires therapeutic plasma monitoring and choice of continuous venous infusion as the administration method. Acute renal or liver failure decrease clearance of linezolid, but renal replacement therapy is capable of restoring clearance back to normal, obviating the need for dosage adjustment. More population pharmacokinetic studies are necessary which will identify and quantify the influence of various factors on clearance and plasma concentrations of linezolid in critically ill patients.

Successful treatment of methicillin-resistant Staphylococcus aureus osteomyelitis with combination therapy using linezolid and rifampicin under therapeutic drug monitoring

Linezolid is an effective antibiotic against most gram-positive bacteria including drug-resistant strains such as methicillin-resistant Staphylococcus aureus. Although linezolid therapy is known to result in thrombocytopenia, dosage adjustment or therapeutic drug monitoring of linezolid is not generally necessary. In this report, however, we describe the case of a 79-year-old woman with recurrent methicillin-resistant S. aureus osteomyelitis that was successfully treated via surgery and combination therapy using linezolid and rifampicin under therapeutic drug monitoring for maintaining an appropriate serum linezolid concentration. The patient underwent surgery for the removal of the artificial left knee joint and placement of vancomycin-impregnated bone cement beads against methicillin-resistant S. aureus after total left knee implant arthroplasty for osteoarthritis. We also initiated linezolid administration at a conventional dose of 600 mg/h at 12-h intervals, but reduced it to 300 mg/h at 12-h intervals on day 9 because of a decrease in platelet count and an increase in serum linezolid trough concentration. However, when the infection exacerbated, we again increased the linezolid dose to 600 mg/h at 12-h intervals and performed combination therapy with rifampicin, considering their synergistic effects and the control of serum linezolid trough concentration via drug interaction. Methicillin-resistant S. aureus infection improved without reducing the dose of or discontinuing linezolid. The findings in the present case suggest that therapeutic drug monitoring could be useful for ensuring the therapeutic efficacy and safety of combination therapy even in patients with osteomyelitis who require long-term antibiotic administration.

Population pharmacokinetics of linezolid in critically ill patients on renal replacement therapy: comparison of equal doses in continuous venovenous haemofiltration and continuous venovenous haemodiafiltration

OBJECTIVES

Few data are available to guide linezolid dosing during renal replacement therapy. The objective of this study was to compare the population pharmacokinetics of linezolid during continuous venovenous haemofiltration (CVVHF, 30 mL/kg/h) and continuous venovenous haemodiafiltration (CVVHDF, 15 mL/kg/h + 15 mL/kg/h).

METHODS

Patients requiring linezolid 600 mg iv every 12 h and CVVHF or CVVHDF were eligible for this prospective study. Seven blood samples were collected over one dosing interval and analysed by a validated chromatographic method. Population pharmacokinetic analysis was undertaken using Pmetrics. Monte Carlo simulations evaluated achievement of a pharmacodynamics target of an AUC from 0-24 h to MIC (AUC0-24/MIC) of 80.

RESULTS

Nine CVVHDF and eight CVVHF treatments were performed in 13 patients. Regimens of CVVHDF and CVVHF were similar. A two-compartment linear model best described the data. CVVHDF was associated with a 20.5% higher mean linezolid clearance than CVVHF, without statistical significance (P = 0.39). Increasing patient weight and decreasing SOFA score were associated with increasing linezolid clearance. The mean (SD) parameter estimates were: clearance (CL), 3.8 (2.2) L/h; volume of the central compartment, 26.5 (10.3) L; intercompartmental clearance constants from central to peripheral, 8.1 (12.1) L/h; and peripheral to central compartments, 3.6 (4.0) L/h. Achievement of pharmacodynamic targets was poor for an MIC of 2 mg/L with the studied dose.

CONCLUSIONS

During CVVHF and CVVHDF, there is profound pharmacokinetic variability of linezolid. Suboptimal achievement of therapeutic targets occurs at the EUCAST breakpoint MIC of 2 mg/L using 600 mg iv every 12 h.

Antibiotic dose optimization in critically ill patients

The judicious use of existing antibiotics is essential for preserving their activity against infections. In the era of multi-drug resistance, this is of particular importance in clinical areas characterized by high antibiotic use, such as the ICU. Antibiotic dose optimization in critically ill patients requires sound knowledge not only of the altered physiology in serious infections - including severe sepsis, septic shock and ventilator-associated pneumonia - but also of the pathogen-drug exposure relationship (i.e. pharmacokinetic/pharmacodynamic index). An important consideration is the fact that extreme shifts in organ function, such as those seen in hyperdynamic patients or those with multiple organ dysfunction syndrome, can have an impact upon drug exposure, and constant vigilance is required when reviewing antibiotic dosing regimens in the critically ill. The use of continuous renal replacement therapy and extracorporeal membrane oxygenation remain important interventions in these patients; however, both of these treatments can have a profound effect on antibiotic exposure. We suggest placing emphasis on the use of therapeutic drug monitoring and dose individualization when optimizing therapy in these settings.

Pharmacokinetic considerations for drugs administered in the critically ill

Significant physiological changes are common among critically ill patients. This case-based review describes the consequences of these changes on the selection and dosing of medications.

How can we ensure effective antibiotic dosing in critically ill patients receiving different types of renal replacement therapy?

Determining appropriate antibiotic dosing for critically ill patients receiving renal replacement therapy (RRT) is complex. Worldwide unstandardized and heterogeneous prescribing of RRT as well as altered patient physiology and pathogen susceptibility all cause drug disposition to be much different to that seen in non-critically ill patients. Significant changes to pharmacokinetic parameters, including volume of distribution and clearance, could be expected, in particular, for antibiotics that are hydrophilic with low plasma protein binding and that are usually primarily eliminated by the renal system. Antibiotic clearance is likely to be significantly increased when higher RRT intensities are used. The combined effect of these factors that alter antibiotic disposition is that non-standard dosing strategies should be considered to achieve therapeutic exposure. In particular, an aggressive early approach to dosing should be considered and this may include administration of a 'loading dose', to rapidly achieve therapeutic concentrations and maximally reduce the inoculum of the pathogen. This approach is particularly important given the pharmacokinetic changes in the critically ill as well as the increased likelihood of less susceptible pathogens. Dose individualization that applies knowledge of the RRT and patient factors causing altered pharmacokinetics remains the key approach for ensuring effective antibiotic therapy for these patients. Where possible, therapeutic drug monitoring should also be used to ensure more accurate therapy. A lack of pharmacokinetic data for antibiotics during the prolonged intermittent RRT and intermittent hemodialysis currently limits evidence-based antibiotic dose recommendations for these patients.

Linezolid bladder irrigation as adjunctive treatment for a vancomycin-resistant Enterococcus faecium catheter-associated urinary tract infection

OBJECTIVE

To describe the first reported successful use of adjunctive linezolid bladder irrigation.

CASE SUMMARY

An 89-year-old woman with 10% TBSA burns developed septic shock and anuric acute kidney insufficiency. She acquired a urinary tract infection caused by vancomycin-resistant Enterococcus faecium (VREfm). Based on clinical status, a linezolid bladder irrigation was initiated in addition to high-dose intravenous linezolid and demonstrated microbiological cure with 7 days of treatment.

DISCUSSION

Linezolid is primarily hepatically cleared and has no labeled indication for urinary tract infections. Anuria adds an additional complication of potentially reduced urinary drug concentrations. Bladder irrigation offers the benefit of achieving high local drug concentrations, but there are no data regarding such a route for linezolid. This case report is the first demonstrating the use, stability, safety, and efficacy of linezolid as a continuous bladder irrigation.

CONCLUSIONS

Linezolid use as a bladder irrigation may be a feasible route of administration in anuric, critically ill patients with VREfm and few antimicrobial options. Further studies are warranted.

How do we use therapeutic drug monitoring to improve outcomes from severe infections in critically ill patients?

High mortality and morbidity rates associated with severe infections in the critically ill continue to be a significant issue for the healthcare system. In view of the diverse and unique pharmacokinetic profile of drugs in this patient population, there is increasing use of therapeutic drug monitoring (TDM) in attempt to optimize the exposure of antibiotics, improve clinical outcome and minimize the emergence of antibiotic resistance. Despite this, a beneficial clinical outcome for TDM of antibiotics has only been demonstrated for aminoglycosides in a general hospital patient population. Clinical outcome studies for other antibiotics remain elusive. Further, there is significant variability among institutions with respect to the practice of TDM including the selection of patients, sampling time for concentration monitoring, methodologies of antibiotic assay, selection of PK/PD targets as well as dose optimisation strategies. The aim of this paper is to review the available evidence relating to practices of antibiotic TDM, and describe how TDM can be applied to potentially improve outcomes from severe infections in the critically ill.

Variability of linezolid concentrations after standard dosing in critically ill patients: a prospective observational study

Introduction

Severe infections in intensive care patients show high morbidity and mortality rates. Linezolid is an antimicrobial drug frequently used in critically ill patients. Recent data indicates that there might be high variability of linezolid serum concentrations in intensive care patients receiving standard doses. This study was aimed to evaluate whether standard dosing of linezolid leads to therapeutic serum concentrations in critically ill patients.

Methods

In this prospective observational study, 30 critically ill adult patients with suspected infections received standard dosing of 600 mg linezolid intravenously twice a day. Over 4 days, multiple serum samples were obtained from each patient, in order to determine the linezolid concentrations by liquid chromatography tandem mass spectrometry.

Results

A high variability of serum linezolid concentrations was observed (range of area under the linezolid concentration time curve over 24 hours (AUC₂₄) 50.1 to 453.9 mg/L, median 143.3 mg*h/L; range of trough concentrations (C_min) < 0.13 to 14.49 mg/L, median 2.06 mg/L). Furthermore, potentially subtherapeutic linezolid concentrations over 24 hours and at single time points (defined according to the literature as AUC₂₄ < 200 mg*h/L and C_min < 2 mg/L) were observed for 63% and 50% of the patients, respectively. Finally, potentially toxic levels (defined as AUC₂₄ > 400 mg*h/L and C_min > 10 mg/L) were observed for 7 of the patients.

Conclusions

A high variability of linezolid serum concentrations with a substantial percentage of potentially subtherapeutic levels was observed in intensive care patients. The findings suggest that therapeutic drug monitoring of linezolid might be helpful for adequate dosing of linezolid in critically ill patients.

Trial registration

Clinicaltrials.gov NCT01793012. Registered 24 January 2013.

Linezolid plasma concentrations and occurrence of drug-related haematological toxicity in patients with gram-positive infections

Retrospective studies have documented a significant association between linezolid (LNZ) plasma concentrations and drug-related haematological toxicity. However, the safe upper threshold level for LNZ plasma trough concentrations (Cmin values) has not been defined with certainty. A prospective observational study was performed aimed at comparing LNZ Cmin values in patients developing drug-related side effects with those measured in patients not experiencing LNZ toxicity. LNZ Cmin values were measured from the first week after starting therapy and were repeated periodically up to the end of treatment. Fifty patients, for a total of 210 LNZ Cmin evaluations, were considered. All patients (n=9) who developed drug-related haematological toxicity also had significantly higher plasma LNZ Cmin values during the first week of therapy (9.0±6.4 mg/L vs. 4.9±3.7 mg/L; P<0.01) and thereafter (9.3±5.4 mg/L vs. 4.4±3.4 mg/L; P<0.01). The significant association between LNZ plasma concentrations and haematological toxicity was also confirmed by multivariate logistic regression analysis including age, serum creatinine and concomitant medications as independent variables. A causal relationship between LNZ concentrations and the risk of developing drug-related haematological toxicity was observed. Accordingly, application of therapeutic drug monitoring may improve the safety outcome of patients receiving LNZ therapy.

Evaluation of antibiotic prescribing patterns in patients receiving sustained low-efficiency dialysis: opportunities for pharmacists

OBJECTIVES

Sustained low-efficiency dialysis (SLED) is a 'hybrid' form of continuous renal replacement therapy; however, there is very limited information on drug disposition during this procedure. Individuals requiring SLED are often critically ill and require antibiotics. The study aim was to evaluate antibiotic orders for patients requiring SLED compared to literature-based recommendations. We also evaluated whether doses were administered as prescribed and assessed clinical and microbiologic cure.

METHODS

A retrospective review was performed over a 2-year period for patients who received concurrent SLED and antibiotic therapy. Demographic data, prescribed antibiotic dosing regimens and doses delivered as prescribed were determined for 10 antibiotics: cefepime (C), daptomycin (Da), doripenem (D), gentamicin (G), imipenem-cilastatin (I), linezolid (L), meropenem (M), piperacillin-tazobactam (P), tobramycin (T) and vancomycin (V). Dosing regimens were compared to recommendations from the literature where available. The incidence of clinical and microbiologic cure was also evaluated.

RESULTS

A total of 87 patients met inclusion criteria: mean age 54 ± 14 years, 60% male, 58% white. Prescribed doses were evidence-based for 37% of Da, 97% of L, 15% of M and 7% of V orders. The majority of discrepancies were due to under-dosing. There were 129 (11%) antibiotic doses missed. Of the 13 patients who met criteria for assessment of clinical and microbiologic cure, 10 achieved a microbiologic cure and none reached clinical cure.

CONCLUSIONS

Prescribed antibiotic dosing regimens varied substantially and under-dosing was common. There is a need to further define appropriate dosing regimens for antibiotics administered during SLED and determine how pharmacists may help to ensure appropriate therapy.

Therapeutic drug monitoring may improve safety outcomes of long-term treatment with linezolid in adult patients

OBJECTIVES

Prolonged treatment with linezolid may cause toxicity. The purpose of this study was to define pharmacodynamic thresholds for improving safety outcomes of linezolid.

METHODS

We performed a retrospective study of patients who had trough (C(min)) and peak (C(max)) plasma levels measured during prolonged linezolid treatment. Dosage adjustments were performed when C(min) ≥10 mg/L and/or AUC₂₄ ≥400 mg/L · h. Patients were divided into two subgroups according to the absence or presence of co-treatment with rifampicin (the linezolid group and the linezolid + rifampicin group, respectively). Data on demographic characteristics, disease, microbiology and haematochemical parameters were collected and outcomes in relation to drug exposure were compared between groups.

RESULTS

A total of 45 patients were included. Dosage adjustments were needed in 40% versus 0% of patients in the linezolid group (n = 35) versus the linezolid + rifampicin group (n = 10), respectively. Patients in the linezolid group had either significantly higher C(min) [3.71 mg/L (1.43-6.38) versus 1.37 mg/L (0.67-2.55), P < 0.001] or AUC₂₄ [212.77 mg/L · h (166.67-278.42) versus 123.33 mg/L · h (97.36-187.94), P < 0.001]. Thrombocytopenia appeared in 51.4% versus 0% of cases in the linezolid group versus the linezolid + rifampicin group, respectively. In 33.3% of those patients who were experiencing thrombocytopenia, therapeutic drug monitoring (TDM)-guided dosage reductions allowed recovery from toxicity and prosecution of therapy with good outcome. A logistic regression model for thrombocytopenia estimated a probability of 50% in the presence of C(min) of 6.53 mg/L and/or of AUC₂₄ of 280.74 mg/L · h.

CONCLUSIONS

Maintenance over time of C(min) between 2 and 7 mg/L and/or of AUC₂₄ between 160 and 300 mg/L · h may be helpful in improving safety outcomes while retaining appropriate efficacy in adult patients receiving prolonged linezolid treatment.

Pharmacokinetics of ampicillin/sulbactam in critically ill patients with acute kidney injury undergoing extended dialysis

BACKGROUND AND OBJECTIVES

The fixed antibacterial combination of ampicillin and sulbactam is frequently used for various infections. Intact kidneys eliminate approximately 71% of ampicillin and 78% of sulbactam. Patients on thrice-weekly low-flux hemodialysis exhibit an ampicillin t(1/2) of 2.3 hours on and 17.4 hours off dialysis. Despite its frequent use in intensive care units, there are no available dosing recommendations for patients with AKI undergoing renal replacement therapy. The aims of this study were to evaluate the pharmacokinetics of ampicillin/sulbactam in critically ill patients with AKI undergoing extended dialysis (ED) and to establish a dosing recommendation for this treatment method.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Twelve critically ill patients with anuric AKI being treated with ED were enrolled in a prospective, open-label, observational pharmacokinetic study. Pharmacokinetics after a single dose of ampicillin/sulbactam (2 g/1 g) was obtained in 12 patients. Multiple-dose pharmacokinetics after 4 days of twice-daily ampicillin/sulbactam (2 g/1 g) was obtained in three patients.

RESULTS

The mean dialyzer clearance for ampicillin/sulbactam was 80.1 ± 7.7/83.3 ± 12.1 ml/min. The t(1/2) of ampicillin and sulbactam in patients with AKI undergoing ED were 2.8 ± 0.8 hours and 3.5 ± 1.5 hours, respectively. There was no significant accumulation using a twice-daily dosage of 2 g/1 g ampicillin/sulbactam.

CONCLUSIONS

Our data suggest that in patients treated with ED using a high-flux dialyzer (polysulphone, 1.3 m(2); blood and dialysate flow, 160 ml/min; treatment time, 480 minutes), a twice-daily dosing schedule of at least 2 g/1 g ampicillin/sulbactam, with one dose given after ED, should be used to avoid underdosing.

Drug dosing consideration in patients with acute and chronic kidney disease-a clinical update from Kidney Disease: Improving Global Outcomes (KDIGO)

Drug dosage adjustment for patients with acute or chronic kidney disease is an accepted standard of practice. The challenge is how to accurately estimate a patient's kidney function in both acute and chronic kidney disease and determine the influence of renal replacement therapies on drug disposition. Kidney Disease: Improving Global Outcomes (KDIGO) held a conference to investigate these issues and propose recommendations for practitioners, researchers, and those involved in the drug development and regulatory arenas. The conference attendees discussed the major challenges facing drug dosage adjustment for patients with kidney disease. In particular, although glomerular filtration rate is the metric used to guide dose adjustment, kidney disease does affect nonrenal clearances, and this is not adequately considered in most pharmacokinetic studies. There are also inadequate studies in patients receiving all forms of renal replacement therapy and in the pediatric population. The conference generated 37 recommendations for clinical practice, 32 recommendations for future research directions, and 24 recommendations for regulatory agencies (US Food and Drug Administration and European Medicines Agency) to enhance the quality of pharmacokinetic and pharmacodynamic information available to clinicians. The KDIGO Conference highlighted the gaps and focused on crafting paths to the future that will stimulate research and improve the global outcomes of patients with acute and chronic kidney disease.

Clinical pharmacokinetic/pharmacodynamic profile of linezolid in severely ill intensive care unit patients

Severely ill Intensive Care Unit (ICU) patients have an increased risk of developing multiresistant Gram-positive infections, largely due to the inappropriate use of antimicrobials. In this study, the pharmacokinetic/pharmacodynamic (PK/PD) profile of linezolid, an antibiotic against Gram-positive infections, was characterised in eight critically ill patients admitted to the ICU. Remarkable variation amongst patients in the PK parameters of linezolid was observed, including a 5-7-fold difference in peak serum concentration (C(max)) (mean±standard deviation 15.70±6.58 mg/L) and 12-h area under the serum concentration-time curve (AUC(0-12)) (96.73±56.45 mg h/L), although the minimum inhibitory concentration (MIC) was similar amongst patients. In particular, variation amongst patients was found in the ratio of AUC(0-24)/MIC (range 31.66-216.82, mean 96.73) and the percentage of time that the serum concentration exceeded the MIC (T>MIC) (range 53.4-100%), two parameters used to predict linezolid efficacy. These variations highlight the importance of individual monitoring of linezolid PK/PD properties in critically ill patients. Furthermore, it was observed that regardless of AUC(0-24)/MIC and T>MIC values, the clinical and microbiological responses of patients were primarily affected by the individual's pathophysiological condition. In summary, these findings point to highly variable PK/PD properties of linezolid in severely ill patients, providing the rationale for targeting linezolid dosage to each individual patient's specific properties. An optimal dosage regimen based on individual PK/PD properties and pathophysiological conditions will help reduce the occurrence of resistance in Gram-positive bacteria.

Is linezolid a risk factor for Gram-negative bacillus infections in intensive care unit patients? A comparative study with vancomycin

BACKGROUND

Linezolid is frequently used in critically ill patients with ventilator-associated pneumonia. Its potent activity against Gram-positive microorganisms and its high tissue penetration may favour Gram-negative colonization and infection. The aim of our study was to evaluate the risk for Gram-negative infections in critically ill patients treated with linezolid or vancomycin.

METHODS

The cases of all patients admitted over an 18-month period to a hepatic intensive care unit for ≥ 1 week, and treated with linezolid or vancomycin, were retrospectively reviewed. The main clinical characteristics and infections due to Gram-negative bacteria in the month after starting linezolid or vancomycin were obtained.

RESULTS

Seventy-one patients treated with linezolid and 68 treated with vancomycin fulfilled the inclusion criteria. Co-morbidities were similar in both groups. Patients on linezolid treatment had a longer stay in the ICU (mean ± standard deviation 41 ± 38 days vs 18.4 ± 13 days), received this treatment later (14.3 ± 15.1 days vs 6.3 ± 6.5 days), had a higher mean serum creatinine concentration (1.71 ± 1.18 mg/dl vs 1.04 ± 1.04 mg/dl), more often required haemodiafiltration (29.6% vs 13.2%), and 30 day-mortality was higher (42.3% vs 20.6%) than in patients receiving vancomycin. More than 95% in both groups received a broad-spectrum beta-lactam in addition to linezolid or vancomycin. The rate of Gram-negative infection during the following month was 28.2% in the linezolid group and 26.5% in the vancomycin group (p > 0.5).

CONCLUSIONS

Linezolid was more frequently used in critically ill patients with longer ICU stay and renal failure. The rate of infection due to Gram-negative microorganisms was similar in patients who received linezolid or vancomycin.

Population pharmacokinetic and pharmacodynamic analysis of linezolid and a hematologic side effect, thrombocytopenia, in Japanese patients

Linezolid is an antimicrobial agent to treat infections by Gram-positive pathogens, including methicillin-resistant Staphylococcus aureus (MRSA). While effective, linezolid treatment frequently is associated with hematological side effects, especially thrombocytopenia. However, little is known about the mechanism of this side effect and the exposure-response relationship. The present population pharmacokinetic/pharmacodynamic (PPK/PD) study was undertaken to elucidate the factors that determine linezolid levels, the relationship between exposure to linezolid and a decrease in platelet counts, and appropriate dosage adjustments based on exposure levels. In total, 50 patients (135 plasma samples) were used for the PPK analysis. The PPK analysis revealed that renal function and severe liver cirrhosis (Child Pugh grade C) significantly affect the pharmacokinetics of linezolid according to the equation clearance (liter/h)=2.85×(creatinine clearance/60.9)0.618×0.472CIR (CIR indicates cirrhosis status; 0 for noncirrhosis, 1 for cirrhosis patients). Using 603 platelet counts from 45 patients, a PPK/PD analysis with a semimechanistic pharmacodynamic model described the relationship between linezolid exposure and platelet counts quantitatively, and the newly constructed model was validated using external data (776 platelet counts from 60 patients). Simulation indicated considerable risks in patients with insufficient renal function (creatinine clearance, ≤30 ml/min) or severe liver cirrhosis. For these patients, a reduced dosage (600 mg/day) would be recommended for sufficient efficacy (area under the concentration-time curve over 24 h in the steady state divided by the MIC, >100) and safety.

Pharmacokinetics of intravenous and oral linezolid in adults with cystic fibrosis

Linezolid is a treatment option for methicillin-resistant Staphylococcus aureus (MRSA) infections in cystic fibrosis (CF) patients. Little is known, however, about its pharmacokinetics in this population. Eight adults with CF were randomized to receive intravenous (i.v.) and oral linezolid at 600 mg twice daily for 9 doses in a crossover design with a 9-day washout. Plasma samples were collected after the first and ninth doses of each phase. Population pharmacokinetic analyses were performed by nonlinear mixed-effects modeling using a previously described 2-compartment model with time-dependent clearance inhibition. Monte Carlo simulation was performed to assess the activities of the linezolid dosing regimens against 42 contemporary MRSA isolates recovered from CF patients. The following pharmacokinetic parameter estimates were observed for the population: absorption rate constant, 1.91 h(-1); clearance, 9.54 liters/h; volume of central compartment, 26.8 liters; volume of peripheral compartment, 17.3 liters; and intercompartmental clearance, 104 liters/h. Linezolid demonstrated nonlinear clearance after 9 doses, which was reduced by a mean of 38.9% (range, 28.8 to 59.9%). Mean bioavailability was 85% (range, 47 to 131%). At steady state, 600 mg given twice daily produced 93.0% and 87.2% probabilities of obtaining the target pharmacodynamic exposure against the MRSA isolates for the i.v. and oral formulations, respectively. Thrice-daily dosing increased the probabilities to 97.0% and 95.6%, respectively. Linezolid pharmacokinetics in these adults with CF were well described by a 2-compartment model with time-dependent clearance inhibition. Standard i.v. and oral dosing regimens should be sufficient to reliably attain pharmacodynamic targets against most MRSA isolates; however, more frequent dosing may be required for isolates with MICs of ≥ 2 μg/ml.