Higher linezolid exposure and higher frequency of thrombocytopenia in patients with renal dysfunction

Linezolid-Induced Thrombocytopenia in Patients with Renal Impairment: A Case Series, Review and Dose Advice

BACKGROUND AND OBJECTIVE

Oral linezolid is often used as alternative therapy for intravenous vancomycin. According to the current guidelines, no dose adjustment has to be made in case of renal impairment. Nevertheless, in our hospital we have seen several patients with renal impairment who developed linezolid-induced thrombocytopenia when linezolid was taken in the standard dose. In this case series and review we want to emphasize the necessity of reviewing the Dutch and international guidelines.

METHODS

We describe five cases with renal impairment that developed linezolid-induced thrombocytopenia in our hospital. A PubMed literature review was conducted to identify other cases and find the optimal dosing regimen for these patients.

RESULTS

Our cases join a long list of cases and available literature about linezolid-induced thrombocytopenia in patients with renal impairment. Less linezolid-induced thrombocytopenia was found, both in our cases and in the literature, after dose reduction of 50%. High linezolid trough concentrations were associated with a higher risk of linezolid-induced thrombocytopenia. Besides renal impairment, other risk factors for developing linezolid-induced thrombocytopenia were also identified, such as low body weight, high daily dose/kg, higher age, longer duration of therapy, low baseline count, malignity, low-dose aspirin and interacting co-medication.

CONCLUSION

Re-evaluation of the current dose advice is necessary. We advocate for a standard dose reduction to 50% after 2 days of standard dosing for all patients with an estimated glomerular filtration of <60 mL/min/1.73 m2. Besides this, therapeutic drug monitoring and thrombocytes monitoring may be executed weekly when patients have renal impairment or other risk factors for developing linezolid-induced thrombocytopenia.

Development and validation of a risk prediction model for linezolid-induced thrombocytopenia in elderly patients

OBJECTIVES

Linezolid is the first oxazolidinone antimicrobial agent developed for treating multi-drug-resistant gram-positive bacterial infections. The study aimed to investigate the risk factors of linezolid (LI)-induced thrombocytopenia (LI-TP) and to develop and validate a risk prediction model to identify elderly patients at high risk of developing LI-TP during linezolid therapy.

METHODS

A retrospective cohort study was performed at Zhongshan Hospital, FuDan University, China. The study involved elderly Chinese patients aged ≥65 years administered with linezolid (600 mg) twice a day between January 2015 and April 2021. We collected the patients' clinical characteristics and demographic data from electronic medical records, and compared the differences between LI-TP patients and those who had not developed thrombocytopenia (NO-TP) after linezolid treatment. The risk prediction model was developed based on the regression coefficient generated from logistic regression model.

RESULTS

A total of 343 inpatients were enrolled from January 2015 to August 2020 and were used as the training set. Among them, 67 (19.5%) developed LI-TP. Multivariate logistic regression analysis revealed that baseline platelet counts <150×109·L-1 (odds ratio (OR)=3.576; p<0.001), age ≥75 years (OR=2.258; p=0.009), estimated glomerular filtration rate (eGFR <60 mL·(min·1.73 m2)-1 (OR=2.553; p=0.002), duration of linezolid therapy ≥10 d (OR=3.218; p<0.001), intensive care unit (ICU) admittance (OR=2.682; p=0.004), concomitant piperacillin-tazobactam (OR=3.863; p=0.006) were independent risk factors for LI-TP in elderly patients. The LI-TP risk prediction model was established using a scoring method based on the regression coefficient and exhibited a good discriminative power, with an area under the curve (AUC) of 0.795 (95% confidence interval (CI) 0.740 to 0.851) and 0.849 (95% CI 0.760 to 0.939) in the training set (n=343) and validation set (n=90) respectively.

CONCLUSIONS

These findings indicate that duration of linezolid therapy, age, eGFR, ICU admittance, baseline platelet counts, concomitant piperacillin-tazobactam were significantly associated with LI-TP in elderly patients. A risk prediction model based on these risk factors showed a good discriminative performance and may be useful for clinicians to identify patients at high risk of developing LI-TP.

Adverse drug events associated with linezolid administration: a real-world pharmacovigilance study from 2004 to 2023 using the FAERS database

Introduction: Linezolid is an oxazolidinone antibiotic that is active against drug-resistant Gram-positive bacteria and multidrug-resistant Mycobacterium tuberculosis. Real-world studies on the safety of linezolid in large populations are lacking. This study aimed to determine the adverse events associated with linezolid in real-world settings by analyzing data from the US Food and Drug Administration (FDA) Adverse Event Reporting System (FAERS). Methods: We retrospectively extracted reports on adverse drug events (ADEs) from the FAERS database from the first quarter of 2004 to that of 2023. By using disproportionality analysis including reporting odds ratio (ROR), proportional reporting ratio (PRR), Bayesian Confidence Propagation Neural Network (BCPNN), along with the multi-item gamma Poisson shrinker (MGPS), we evaluated whether there was a significant association between linezolid and ADE. The time to onset of ADE was further analyzed in the general population and within each age, weight, reporting population, and weight subgroups. Results: A total of 11,176 reports of linezolid as the "primary suspected" drug and 263 significant adverse events of linezolid were identified, including some common adverse events such as thrombocytopenia (n = 1,139, ROR 21.98), anaemia (n = 704, ROR 7.39), and unexpected signals that were not listed on the drug label such as rhabdomyolysis (n = 90, ROR 4.33), and electrocardiogram QT prolonged (n = 73, ROR 4.07). Linezolid-induced adverse reactions involved 27 System Organ Class (SOC). Gender differences existed in ADE signals related to linezolid. The median onset time of all ADEs was 6 days, and most ADEs (n = 3,778) occurred within the first month of linezolid use but some may continue to occur even after a year of treatment (n = 46). Conclusion: This study reports the time to onset of adverse effects in detail at the levels of SOC and specific preferred term (PT). The results of our study provide valuable insights for optimizing the use of linezolid and reducing potential side effects, expected to facilitate the safe use of linezolid in clinical settings.

Antibiotic Myths for the Infectious Diseases Clinician

Antimicrobials are commonly prescribed and often misunderstood. With more than 50% of hospitalized patients receiving an antimicrobial agent at any point in time, judicious and optimal use of these drugs is paramount to advancing patient care. This narrative will focus on myths relevant to nuanced consultation from infectious diseases specialists, particularly surrounding specific considerations for a variety of antibiotics.

Bayesian prediction-based individualized dosing of anti-methicillin-resistant Staphylococcus aureus treatment: Recent advancements and prospects in therapeutic drug monitoring

As one of the efficient techniques for TDM, the population pharmacokinetic (popPK) model approach for dose individualization has been developed due to the rapidly growing innovative progress in computer technology and has recently been considered as a part of model-informed precision dosing (MIPD). Initial dose individualization and measurement followed by maximum a posteriori (MAP)-Bayesian prediction using a popPK model are the most classical and widely used approach among a class of MIPD strategies. MAP-Bayesian prediction offers the possibility of dose optimization based on measurement even before reaching a pharmacokinetically steady state, such as in an emergency, especially for infectious diseases requiring urgent antimicrobial treatment. As the pharmacokinetic processes in critically ill patients are affected and highly variable due to pathophysiological disturbances, the advantages offered by the popPK model approach make it highly recommended and required for effective and appropriate antimicrobial treatment. In this review, we focus on novel insights and beneficial aspects of the popPK model approach, especially in the treatment of infectious diseases with anti-methicillin-resistant Staphylococcus aureus agents represented by vancomycin, and discuss the recent advancements and prospects in TDM practice.

Risk factors for mortality after linezolid treatment of vancomycin-resistant Enterococcus bloodstream infection

OBJECTIVES

We analyzed the risk factors affecting linezolid treatment outcome in vancomycin-resistant Enterococcus (VRE) bloodstream infection (BSI).

METHODS

We conducted a multicenter observational study of patients who received linezolid 600 mg every 12 hours for VRE BSI. The primary outcome was 28-day mortality. The estimated area under the concentration-time curve and trough concentration were calculated. Multivariable logistic regression was used for the outcome analysis.

RESULTS

A total of 170 patients were included: 114 (67.1%) survived and 56 (32.9%) did not. A total of 26 (18.2%) isolates showed a linezolid minimum inhibitory concentration (MIC) of ≤1 mg/l, 113 (79.0%) of 2 mg/l, and 4 (2.8%) of 4 mg/l. The univariable analysis showed that the linezolid MIC and concentration-time curve/MIC were not associated with mortality (P = 0.95 and P = 0.42, respectively). After adjusting for underlying comorbidity and disease severity, the linezolid dose per body weight (LDBW), body height, and interaction between them were independent risks for mortality. Marginal analysis showed that increasing the LDBW was protective in patients with a body height <160 cm. A trough concentration of >12.2 mg/l was a risk factor for thrombocytopenia.

CONCLUSION

The LDBW and body height were interactively associated with clinical outcomes of linezolid treatment for VRE BSI.

Use of Japanese big data from electronic medical records to investigate risk factors and identify their high-risk combinations for linezolid-induced thrombocytopenia

PURPOSE

Thrombocytopenia is a major event associated with linezolid (LZD) therapy. Factors affecting LZD-induced thrombocytopenia (LIT) have been reported in previous studies. However, several issues pertaining to LIT have not yet been clarified. In the present study, we used Japanese big data to investigate associated factors and their high-risk combinations that influence LIT.

METHODS

Patients administered LZD between May 2006 and October 2020 were included in this study. LIT was defined as either a 30% or more reduction from the baseline platelets or platelet values of < 100,000/µL. We evaluated factors affecting LIT and combinations of factors that alter LIT risk according to a decision tree (DT) analysis, a typical machine learning method.

RESULTS

We successfully enrolled 1399 patients and LIT occurred in 44.7% of the patients (n = 626). We classified the laboratory data on renal function, LZD duration, age, and body weight (BW) into smaller categories. The results of multivariate analysis showed that prolonged LZD therapy, BW < 45 kg, estimated glomerular filtration rate (eGFR) < 30 mL/min/1.73 m², and dialysis were risk factors for LIT. The DT analysis revealed that the highest risk was a combination of LZD duration ≥ 14 days and eGFR < 30 mL/min/1.73 m².

CONCLUSIONS

The present study extracted four risk factors and identified high-risk combinations for LIT. Patients with these risk factors should be closely monitored.

Hematological toxicities associated with linezolid therapy in adults: key findings and clinical considerations

INTRODUCTION

Linezolid can cause serious adverse effects including thrombocytopenia and anemia. Here, we focus specifically on linezolid-related hematological toxicity in adult patients requiring prolonged drug treatment.

AREAS COVERED

We review the available evidence on the likelihood of hematological toxicity in adult patients treated with linezolid, with a focus on the main risk factors and strategies to prevent this adverse event. A MEDLINE PubMed search for articles published from January 2000 to May 2022 was completed matching the terms linezolid, hematology, hematological toxicity, anemia, and thrombocytopenia. Moreover, additional studies were identified from the reference lists of retrieved articles.

EXPERT OPINION

Thrombocytopenia is the major concern with administration of linezolid for Gram-positive infections, whereas anemia is more common in patients with tuberculosis. The important clinical risk factors for the development of linezolid-related thrombocytopenia are aging, renal dysfunction, low baseline platelet count, duration of treatment, and linezolid plasma trough concentrations >8 mg/L. Patients receiving linezolid for extended periods of time or patient populations with increased risk of altered drug pharmacokinetics would benefit from therapeutic drug monitoring or from the availability of toxico-dynamic predictive models to optimize linezolid dosing.

A Retrospective Study to Compare the Incidence of Hyponatremia after Administration between Linezolid and Tedizolid

Linezolid (LZD) and Tedizolid (TZD) are oxazolidinone antibiotic for meticillin-resistant Staphylococcus aureus (MRSA). Severe hyponatremia after LZD administration have been reported. Severe hyponatremia cause seizures, unconsciousness, and even death. Therefore, we conducted a study to assess the change of serum sodium level after LZD and TZD therapy. We enrolled 67 patients treated with LZD and 28 treated with TZD. We monitored the serum sodium level from the administration to 14 days after administration of oxazolidinone drug. Hyponatremia was defined a sodiuln level ≤134 mmol/L after the initiation of oxazolidinone drug. The frequency of hyponatremia in the LZD group was significantly higher than that in the TZD group (39.7% vs. 11.1%, p < 0.05). The rate of patients administered by injection was significantly higher than in the LZD group than in the TZD group (52.9% vs. 14.8%, p < 0.01). Multiple logistic regression analyses identified the albumin level before the oxazolidinone drug therapy as the independent variables associated with the development of hyponatremia. We revealed that TZD is safer than LZD in terms of hyponatremia. Therefore, cases that LZD is administered by injection should be used more carefully with hyponatremia in patients with low albumin level.

A standard dose of linezolid puts patients with hepatic impairment at risk of overexposure

PURPOSE

The purpose of this retrospective observational study conducted in patients with hepatic impairment was to assess the variability of linezolid trough concentrations, to determine the risk factors for linezolid overexposure, and to investigate the effect of linezolid overexposure on linezolid-induced thrombocytopenia.

METHODS

All enrolled patients received a standard dose (600 mg every 12 h) of linezolid and underwent therapeutic drug monitoring. The Child-Pugh-Turcotte score was used to divide patients into three groups: mild, moderate, and severe hepatic impairment. The risk factors for linezolid overexposure (C_min > 8 mg/L) and linezolid-induced thrombocytopenia were examined using logistic regression. And the Kaplan-Meier curve was used to describe the association between linezolid overexposure and linezolid-induced thrombocytopenia.

RESULTS

Seventy-seven patients were included, 37 (48.1%) of whom experienced linezolid overexposure. Patients with severe hepatic impairment had a substantially higher median C_min of linezolid than those with mild (20.7 mg/L vs 5.51 mg/L, P < 0.001) or moderate (20.7 mg/L vs 6.70 mg/L, P = 0.001) hepatic impairment. Severe hepatic impairment was significantly associated with linezolid overexposure (OR 7.037, 95%CI 1.426-34.727, P = 0.017). After linezolid treatment, linezolid-induced thrombocytopenia occurred in 32 (41.6%) patients, and C_min > 8 mg/L was a significant predictor of linezolid-induced thrombocytopenia (OR 3.024, 95%CI 1.083-8.541, P = 0.035).

CONCLUSION

Patients with hepatic impairment who received standard doses of linezolid are at greater risk of linezolid overexposure, which may lead to a higher incidence of linezolid-induced thrombocytopenia.

Pharmacokinetic and pharmacodynamic simulation for the quantitative risk assessment of linezolid-associated thrombocytopenia

WHAT IS KNOWN AND OBJECTIVE

Linezolid (LZD) may cause thrombocytopenia, which can result in discontinuation of treatment. In this study, the blood LZD trough concentration was estimated based on population pharmacokinetic (PK) parameters derived from two previously published models in the Japanese population to determine the rate of achieving the target trough value when the risk of thrombocytopenia is low and to clarify its relationship with the onset of thrombocytopenia.

METHODS

This study included adult patients hospitalized at Shimane University Hospital, who received LZD treatment for at least 4 days from January 2010 to December 2017. Patients whose platelet count fell below 70% before LZD administration were categorized as the thrombocytopenic group. Patient PK parameters were calculated based on the population PK models described by Matsumoto et al. and Sasaki et al., and these parameters were designated A and B, respectively. Based on these parameters, the rate of achieving an LZD trough concentration of less than 8 μg/ml, which is the safety target achievement rate, was calculated using a random simulation for each patient. We further analysed the association between the incidence of thrombocytopenia and patient factors, including safety target achievement rate, through univariate, multivariate, and receiver operating characteristic (ROC) analyses.

RESULTS AND DISCUSSION

Patients (n = 77) aged 72 ± 11 years and weighing 56.7 ± 10.9 kg, with a creatinine clearance (CL_cr ) of 60.5 ± 47.2 ml/min and a cirrhosis prevalence of 9.1%, were analysed. All patients received LZD at a dose of 600 mg twice daily for a total of 10.9 ± 8.9 days. Univariate analyses revealed significant differences (p < 0.05) in the duration of LZD therapy, serum creatinine, creatinine clearance, LZD clearance, and the safety target achievement rate for parameters A and B between the thrombocytopenic and non-thrombocytopenic groups. A multivariate analysis of these factors stratified with the cutoff values obtained by ROC analysis revealed that the duration of LZD therapy and the safety target achievement rates for parameters A and B were significant factors (odds ratios for duration of LZD therapy: 7.436 [95% confidence interval (CI): 1.918-28.831] and 4.712 [95% CI: 1.567-14.163]; odds ratio for safety target achievement rate: 0.060 [95% CI: 0.016-0.232] and 0.167 [95% CI: 0.056-0.498] for parameters A and B, respectively). When the safety target achievement rates for patients treated with LZD were compared between the thrombocytopenic and non-thrombocytopenic groups, the safety target achievement rate was higher in the non-thrombocytopenic group in both the patients treated with LZD for less than 10 days and those for 10 days or more. Therefore, the safety target achievement rate estimated by the PK/PD simulation may represent to be an important index for risk assessment of LZD-induced thrombocytopenia.

WHAT IS NEW AND CONCLUSION

The risk of LZD-induced thrombocytopenia, which increased with the duration of LZD therapy, may be predicted using the safety target achievement rate obtained by the blood concentration simulation.

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.

Target Therapeutic Ranges of Anti-MRSA Drugs, Linezolid, Tedizolid and Daptomycin, and the Necessity of TDM

The target therapeutic ranges of vancomycin, teicoplanin, and arbekacin have been determined, and therapeutic drug monitoring (TDM) is performed in clinical practice. However, TDM is not obligatory for daptomycin, linezolid, or tedizolid. In this study, we examined whether TDM will be necessary for these 3 drugs in the future. There was no significant difference in therapeutic effects on acute bacterial skin and skin structure infection between linezolid and tedizolid by meta-analysis. Concerning the therapeutic effects on pneumonia, the rate of effectiveness after treatment with tedizolid was significantly lower than with linezolid. With respect to safety, the incidences of gastrointestinal adverse events and blood/lymphatic system disorders related to tedizolid were significantly lower than those related to linezolid. Linezolid exhibits potent therapeutic effects on pneumonia, but the appearance of adverse reactions is indicated as a problem. There was a dose-dependent decrease in the platelet count, and the target trough concentration (C_trough) was estimated to be 4-6 or 2-7 µg/mL in accordance with the patient's condition. The efficacy of linezolid may be obtained while minimizing the appearance of adverse reactions by performing TDM. The target therapeutic range of tedizolid cannot be achieved in immunocompromised or severe patients. Therefore, we concluded that TDM was unnecessary, considering step-down therapy with oral drugs, use in non-severe patients, and high-level safety. Concerning daptomycin, high-dose administration is necessary to achieve an area under the curve (AUC) of ≥666 as an index of efficacy. To secure its safety, C_trough (<20 µg/mL) monitoring is important. Therefore, TDM is necessary.

New Mutations in cls Lead to Daptomycin Resistance in a Clinical Vancomycin- and Daptomycin-Resistant Enterococcus faecium Strain

Daptomycin (DAP), a last-resort antibiotic for treating Gram-positive bacterial infection, has been widely used in the treatment of vancomycin-resistant enterococci (VRE). Resistance to both daptomycin and vancomycin leads to difficulties in controlling infections of enterococci. A clinical multidrug-resistant Enterococcus faecium EF332 strain that shows resistance to both daptomycin and vancomycin was identified, for which resistance mechanisms were investigated in this work. Whole-genome sequencing and comparative genomic analysis were performed by third-generation PacBio sequencing, showing that E. faecium EF332 contains four plasmids, including a new multidrug-resistant pEF332-2 plasmid. Two vancomycin resistance-conferring gene clusters vanA and vanM were found on this plasmid, making it the second reported vancomycin-resistant plasmid containing both clusters. New mutations in chromosomal genes cls and gdpD that, respectively, encode cardiolipin synthase and glycerophosphoryl diester phosphodiesterase were identified. Their potential roles in leading to daptomycin resistance were further investigated. Through molecular cloning and phenotypic screening, two-dimensional thin-layer chromatography, fluorescence surface charge test, and analysis of cardiolipin distribution patterns, we found that mutations in cls decrease surface negative charges of the cell membrane (CM) and led to redistribution of lipids of CM. Both events contribute to the DAP resistance of E. faecium EF332. Mutation in gdpD leads to changes in CM phospholipid compositions, but cannot confer DAP resistance. Neither mutation could result in changes in cellular septa. Therefore, we conclude that the daptomycin resistance of E. faecium EF332 is conferred by new cls mutations. This work reports the genetic basis for vancomycin and daptomycin resistance of a multidrug-resistant E. faecium strain, with the finding of new mutations of cls that leads to daptomycin resistance.

Renal replacement therapy and concurrent fluconazole therapy increase linezolid-related thrombocytopenia among adult patients

Linezolid has been reported to be associated with thrombocytopenia. However, limited information is available on susceptibility to thrombocytopenia after linezolid usage. We aimed to investigate the risk factors for linezolid-associated thrombocytopenia (LAT). We conducted a retrospective cohort study of patients aged ≥ 18 years who received linezolid for ≥ 5 d during hospitalization in 2019. Information was extracted from electronic medical records. Thrombocytopenia was defined as a platelet count of < 100 × 10⁹/L or a reduction from baseline ≥ 25%. Binary logistic regression and survival analyses were used to evaluate the risk factors for LAT. A total of 98 patients were enrolled. Thrombocytopenia occurred in 53.1% patients, with a median of 9 d after initiation of linezolid. There was no significant difference in the mortality or proportion of platelet transfusions between patients with and without thrombocytopenia. A higher risk of LAT was found in patients who received renal replacement therapy (RRT) (OR 4.8 [1.4–16.4]), or concurrent fluconazole (OR 3.5 [1.2–9.8]). Patients who received RRT (8 vs. 15 d) or concurrent fluconazole (11 vs. 15 d) had a shorter median time to develop thrombocytopenia. Those who simultaneously received RRT and fluconazole had the shortest median of time (6.5 d) and the highest risk of developing thrombocytopenia (87.5%).

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.

Dosage Strategy of Linezolid According to the Trough Concentration Target and Renal Function in Chinese Critically Ill Patients

Background: Linezolid is associated with myelosuppression, which may cause failure in optimally treating bacterial infections. The study aimed to define the pharmacokinetic/toxicodynamic (PK/TD) threshold for critically ill patients and to identify a dosing strategy for critically ill patients with renal insufficiency.

Methods: The population pharmacokinetic (PK) model was developed using the NONMEM program. Logistic regression modeling was conducted to determine the toxicodynamic (TD) threshold of linezolid-induced myelosuppression. The dosing regimen was optimized based on the Monte Carlo simulation of the final model.

Results: PK analysis included 127 linezolid concentrations from 83 critically ill patients at a range of 0.25–21.61 mg/L. Creatinine clearance (CrCL) was identified as the only covariate of linezolid clearance that significantly explained interindividual variability. Thirty-four (40.97%) of the 83 patients developed linezolid-associated myelosuppression. Logistic regression analysis showed that the trough concentration (Cmin) was a significant predictor of myelosuppression in critically patients, and the threshold for Cmin in predicting myelosuppression with 50% probability was 7.8 mg/L. The Kaplan–Meier plot revealed that the overall median time from the initiation of therapy to the development of myelosuppression was 12 days. Monte Carlo simulation indicated an empirical dose reduction to 600 mg every 24 h was optimal to balance the safety and efficacy in critically ill patients with CrCL of 30–60 ml/min, 450 mg every 24 h was the alternative for patients with CrCL &lt;30 ml/min, and 600 mg every 12 h was recommended for patients with CrCL ≥60 ml/min.

Conclusion: Renal function plays a significant role in linezolid PKs for critically ill patients. A dose of 600 mg every 24 h was recommended for patients with CrCL &lt;60 ml/min to minimize linezolid-induced myelosuppression.

Initial trough concentration may be beneficial in preventing linezolid-induced thrombocytopenia

We assessed whether prospective therapeutic drug monitoring to optimise the therapeutic range could prevent linezolid-induced thrombocytopenia. This prospective interventional study was conducted from September 2017 to October 2020 among 37 adult patients receiving linezolid. Patients were administered one of the following two initial dosages: 600 mg twice or once daily for patients with a creatinine clearance rate of ≥50 or <50 mL/min, respectively. Linezolid dosage adjustment was performed on days 3-5 based on the trough concentration. The serum linezolid levels in 22 and 15 patients were within and above the therapeutic range (2-7 µg/mL), respectively. The incidence of thrombocytopenia was significantly lower among patients whose linezolid levels were within the therapeutic range (4.5%;1/22) than in those whose levels were above the therapeutic range (80%; 12/15). It is important to maintain the linezolid level within the therapeutic range at the first therapeutic drug monitoring to prevent thrombocytopenia.

Importance and Reality of TDM for Antibiotics Not Covered by Insurance in Japan

Under the Japanese health insurance system, medicines undergoing therapeutic drug monitoring (TDM) can be billed for medical fees if they meet the specified requirements. In Japan, TDM of vancomycin, teicoplanin, aminoglycosides, and voriconazole, which are used for the treatment of infectious diseases, is common practice. This means the levels of antibiotics are measured in-house using chromatography or other methods. In some facilities, the blood and/or tissue concentrations of other non-TDM drugs are measured by HPLC and are applied to treatment, which is necessary for personalized medicine. This review describes personalized medicine based on the use of chromatography as a result of the current situation in Japan.

Therapeutic Drug Monitoring of Antibiotics: Defining the Therapeutic Range

PURPOSE

In the present narrative review, the authors aimed to discuss the relationship between the pharmacokinetic/pharmacodynamic (PK/PD) of antibiotics and clinical response (including efficacy and toxicity). In addition, this review describes how this relationship can be applied to define the therapeutic range of a particular antibiotic (or antibiotic class) for therapeutic drug monitoring (TDM).

METHODS

Relevant clinical studies that examined the relationship between PK/PD of antibiotics and clinical response (efficacy and response) were reviewed. The review (performed for studies published in English up to September 2021) assessed only commonly used antibiotics (or antibiotic classes), including aminoglycosides, beta-lactam antibiotics, daptomycin, fluoroquinolones, glycopeptides (teicoplanin and vancomycin), and linezolid. The best currently available evidence was used to define the therapeutic range for these antibiotics.

RESULTS

The therapeutic range associated with maximal clinical efficacy and minimal toxicity is available for commonly used antibiotics, and these values can be implemented when TDM for antibiotics is performed. Additional data are needed to clarify the relationship between PK/PD indices and the development of antibiotic resistance.

CONCLUSIONS

TDM should only be regarded as a means to achieve the main goal of providing safe and effective antibiotic therapy for all patients. The next critical step is to define exposures that can prevent the development of antibiotic resistance and include these exposures as therapeutic drug monitoring targets.

Linezolid Population Pharmacokinetics in South African Adults with Drug-Resistant Tuberculosis

Linezolid is widely used for drug-resistant tuberculosis (DR-TB) but has a narrow therapeutic index. To inform dose optimization, we aimed to characterize the population pharmacokinetics of linezolid in South African participants with DR-TB and explore the effect of covariates, including HIV coinfection, on drug exposure. Data were obtained from pharmacokinetic substudies in a randomized controlled trial and an observational cohort study, both of which enrolled adults with drug-resistant pulmonary tuberculosis. Participants underwent intensive and sparse plasma sampling. We analyzed linezolid concentration data using nonlinear mixed-effects modeling and performed simulations to estimate attainment of putative efficacy and toxicity targets. A total of 124 participants provided 444 plasma samples; 116 were on the standard daily dose of 600 mg, while 19 had dose reduction to 300 mg due to adverse events. Sixty-one participants were female, 71 were HIV-positive, and their median weight was 56 kg (interquartile range [IQR], 50 to 63). In the final model, typical values for clearance and central volume were 3.57 liters/h and 40.2 liters, respectively. HIV coinfection had no significant effect on linezolid exposure. Simulations showed that 600-mg dosing achieved the efficacy target (area under the concentration-time curve for the free, unbound fraction of the drug [[Formula: see text] at a MIC level of 0.5 mg/liter) with 96% probability but had 56% probability of exceeding safety target ([Formula: see text]. The 300-mg dose did not achieve adequate efficacy exposures. Our model characterized population pharmacokinetics of linezolid in South African patients with DR-TB and supports the 600-mg daily dose with safety monitoring.

Model Based Identification of Linezolid Exposure-toxicity Thresholds in Hospitalized Patients

Evidence supports linezolid therapeutic drug monitoring as the exposure-response relationship has been identified for toxicity among patients receiving linezolid, but the data to establish the upper limit are limited and the published toxicity thresholds range widely. The purpose of this study was to determine the linezolid exposure-toxicity thresholds to improve the safety of linezolid. This is a multicenter retrospective study of adult patients treated with linezolid from 2018 to 2019. The population pharmacokinetic model of linezolid was established based on 270 plasma concentrations in 152 patients, which showed creatinine clearance and white cell count are covariates affecting the clearance of linezolid, and serum albumin is the covariate affecting the volume of distribution. Classification and regression tree analysis was used to determine the linezolid exposure thresholds associated with an increased probability of toxicity. Among 141 patients included for toxicity analysis, the rate of occurring toxicity was significantly higher among patients with an AUC_{0-24, d1} ≥163 mg h/L, AUC_{0-24, d2} ≥207 mg h/L, AUC_{0-24, ss} ≥210 mg h/L, and C_min,d2 ≥6.9 mg/L, C_min,ss ≥6.9 mg/L, while no threshold was discovered for C_{min, d1}. Those exposure thresholds and duration of linezolid treatment were independently associated with linezolid-related toxicity in the logistic regression analyses. In addition, the predictive performance of the AUC_0-24 and C_min thresholds at day 2 and steady state were close. Considering that the AUC estimation is cumbersome, C_min threshold at 48 h and steady state with a value of ≥6.9 mg/L is recommended to improve safety, especially for patients with renal insufficiency and patients with low serum albumin.

A risk factor-based predictive model for linezolid-induced anaemia: A 7-year retrospective study

WHAT IS KNOWN AND OBJECTIVE

The primary adverse reaction of linezolid is haematological toxicity, leading to thrombocytopenia and anaemia. This study aimed to investigate the risk factors of linezolid-induced anaemia (LI-AN) and establish a predictive model by multivariate logistic regression model analysis to predict LI-AN risks in Chinese adult patients.

METHODS

Demographic and clinical data of patients who underwent linezolid therapy for more than three days between January 2014 and December 2020 in Zhongshan Hospital, Fudan University, were retrieved from the hospital's electronic medical record for analysis. Multivariate logistic regression analysis was employed to establish a predictive model, whose predictability was further evaluated by the area under the receiver operating characteristic (ROC) curve.

RESULTS AND DISCUSSION

The study comprised 298 patients among the 2322 patients who underwent linezolid treatment between 2014 and 2020. Among the 298 patients, 32 (10.7%) developed anaemia with an average of 11.4 (SD 6.2) days after the initiation of linezolid therapy. Multivariate logistic analysis revealed that age ≥60 years (odds ratio [OR] 2.815, 95% confidence interval [CI] 1.242-6.379), higher total bilirubin (TBi) (OR 1.031, 95% CI 1.011-1.051), eGFR < 60 ml/(min·1.73 m² ) (OR 2.537, 95% CI 1.054-6.106), duration of linezolid therapy (DLT) (OR 1.091, 95% CI 1.023-1.163) and intensive care unit (ICU) admittance (OR 2.664, 95% CI 1.150-6.174) were the independent risk factors for anaemia occurrence among patients receiving linezolid therapy. A logistic regression equation based on the five risk factors was subsequently established and transformed to obtain the calculation formula of the combined predictor: Y_{(Combined predictor)}  = X_TBi  + 34.5 × X_Age≥60  + 31.1 × X_eGFR<60  + 32.7 × X_ICU  + 2.9 × X_DLT , (where Age ≥60 years, yes = 1, no = 0; eGFR < 60 ml/(min·1.73 m² ), yes = 1, no = 0; ICU admittance, yes = 1, no = 0). The area under the ROC curve of the combined predictors equation was 0.773 with an optimal cut-off point value of 92.4, corresponding to a 75.0% sensitivity and 76.7% specificity.

WHAT IS NEW AND CONCLUSION

LI-AN is associated with age (≥60 years), higher TBi, eGFR < 60 ml/(min·1.73 m² ), DLT and ICU admittance. Physicians should thus calculate the combined predictor value at the beginning of linezolid treatment to predict and evaluate the risk of LI-AN. An optimal cut-off value larger than 92.4 indicates that the patient has a higher LI-AN risk. As such, Hb levels should be monitored regularly, and dosage regimens adjusted accordingly to prevent anaemia occurrence. This study provides an evidence-based logistic model that reduces LI-AN incidences and promotes the safe clinical use of linezolid.

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.

Therapeutic Drug Monitoring Can Improve Linezolid Dosing Regimens in Current Clinical Practice: A Review of Linezolid Pharmacokinetics and Pharmacodynamics

Linezolid is an antibiotic used to treat infections caused by drug-resistant gram-positive organisms, including vancomycin-resistant Enterococcus faecium, multi-drug resistant Streptococcus pneumoniae, and methicillin-resistant Staphylococcus aureus. The adverse effects of linezolid can include thrombocytopenia and neuropathy, which are more prevalent with higher exposures and longer treatment durations. Although linezolid is traditionally administered at a standard 600 mg dose every 12 hours, the resulting exposure can vary greatly between patients and can lead to treatment failure or toxicity. The efficacy and toxicity of linezolid are determined by the exposure achieved in the patient; numerous clinical and population pharmacokinetics (popPK) studies have identified threshold measurements for both parameters. Several special populations with an increased need for linezolid dose adjustments have also been identified. Therapeutic Drug Monitoring (TDM) is a clinical strategy that assesses the response of an individual patient and helps adjust the dosing regimen to maximize efficacy while minimizing toxicity. Adaptive feedback control and model-informed precision dosing are additional strategies that use Bayesian algorithms and PK models to predict patient-specific drug exposure. TDM is a very useful tool for patient populations with sparse clinical data or known alterations in pharmacokinetics, including children, patients with renal insufficiency or those receiving renal replacement therapy, and patients taking co-medications known to interact with linezolid. As part of the clinical workflow, clinicians can use TDM with the thresholds summarized from the current literature to improve linezolid dosing for patients and maximize the probability of treatment success.

From Therapeutic Drug Monitoring to Model-Informed Precision Dosing for Antibiotics

Therapeutic drug monitoring (TDM) and model-informed precision dosing (MIPD) have evolved as important tools to inform rational dosing of antibiotics in individual patients with infections. In particular, critically ill patients display altered, highly variable pharmacokinetics and often suffer from infections caused by less susceptible bacteria. Consequently, TDM has been used to individualize dosing in this patient group for many years. More recently, there has been increasing research on the use of MIPD software to streamline the TDM process, which can increase the flexibility and precision of dose individualization but also requires adequate model validation and re-evaluation of existing workflows. In parallel, new minimally invasive and noninvasive technologies such as microneedle-based sensors are being developed, which-together with MIPD software-have the potential to revolutionize how patients are dosed with antibiotics. Nonetheless, carefully designed clinical trials to evaluate the benefit of TDM and MIPD approaches are still sparse, but are critically needed to justify the implementation of TDM and MIPD in clinical practice. The present review summarizes the clinical pharmacology of antibiotics, conventional TDM and MIPD approaches, and evidence of the value of TDM/MIPD for aminoglycosides, beta-lactams, glycopeptides, and linezolid, for which precision dosing approaches have been recommended.

Classification Tree Analysis Based On Machine Learning for Predicting Linezolid-Induced Thrombocytopenia

Linezolid-induced thrombocytopenia is related to linezolid exposure, baseline platelet count and patient background. Although the relationship usually reflects the time of onset of thrombocytopenia, if the platelet maturation process is taken into account, the platelet decrease can be considered to have started at the beginning of treatment. To predict linezolid-induced thrombocytopenia, classification and regression tree (CART) analysis based on machine learning has been applied to identify predictive factors and cutoff values. We examined 74 patient data with or without linezolid-induced thrombocytopenia. Linezolid concentration and platelet count change, baseline platelet count, age, body weight and creatinine clearance estimate were evaluated as predictive factors for linezolid-induced thrombocytopenia. CART analysis selected the final tree containing two cutoff values: a platelet count reduction to less than 2.3% from baseline at 96 h after the initial dose and a linezolid concentration greater than or equal to 13.5 mg/L at 96 h after the initial dose. The targets for therapeutic intervention were concluded to be the linezolid concentration and the platelet change from baseline at 96 h after the initial dose. These cutoff values occur prior to the onset of thrombocytopenia and should be monitored to avoid linezolid-induced thrombocytopenia.

Analysis of the risk factors of linezolid-related haematological toxicity in Chinese patients

WHAT IS KNOWN AND OBJECTIVES

Haematological toxicity including thrombocytopenia, anaemia and leucopenia is the main adverse events of linezolid (LZD) therapy. This study aimed to investigate the risk factors for LZD-induced haematological toxicity and define the threshold of plasma trough concentration to minimize the haematological toxicity.

METHODS

145 patients who received LZD for more than 10 days were retrospectively reviewed to determine the incidence of LZD-induced haematological toxicity. Meanwhile, the risk factors of haematological toxicity were confirmed by univariate and multivariate logistic regression analysis.

RESULTS AND DISCUSSION

9 (6.2%) patients developed leucopenia, while 52 (35.9%) and 26 (17.9%) patients developed thrombocytopenia and anaemia, respectively. The estimated glomerular filtration rate (eGFR) <90 ml/min/1.73 m² (OR, 2.744; 95% CI, 1.117-6.734; p = 0.028) and baseline platelet count <200 × 10⁹ /L (OR, 6.817; 95% CI, 2.870-16.193; p < 0.0001) were found to be significant risk factors for LZD-related thrombocytopenia. Aspartate aminotransferase (AST) >80 U/L (OR, 4.844; 95% CI, 1.207-19.451; p = 0.026) and eGFR <90 ml/min/1.73 m² (OR, 7.132; 95% CI, 2.088-24.357; p = 0.002) were the risk factors for LZD-related anaemia. However, no significant risk factors were identified for LZD-related leucopenia. Moreover, LZD plasma trough concentration >8 mg/L [OR, 3.047; 95% CI, 1.233-7.539; p = 0.016] could be a predictor for the development of thrombocytopenia and anaemia.

WHAT IS NEW AND CONCLUSION

Hepatic and/or renal dysfunction are the risk factors for LZD-related haematological toxicity, while the target plasma trough concentration within 8 mg/L via dose reduction could minimize the haematological toxicity induced by LZD.

Proactive therapeutic drug monitoring (TDM) may be helpful in managing long-term treatment with linezolid safely: findings from a monocentric, prospective, open-label, interventional study

BACKGROUND

Thrombocytopenia may be a dose-dependent adverse effect of linezolid therapy.

OBJECTIVES

To assess whether proactive therapeutic drug monitoring (TDM) could be helpful in preventing and/or in recovering from the occurrence of linezolid-induced thrombocytopenia during long-term treatment.

METHODS

This was a monocentric, prospective, open-label, interventional study conducted between June 2015 and December 2017 among adult patients receiving >10 days of linezolid therapy and undergoing proactive TDM (desired trough level 2-8 mg/L) and platelet count assessment at day 3-5 and then once weekly up to the end of treatment.

RESULTS

Sixty-one patients were included. Twenty-eight (45.9%) always had desired trough level (group A) and 33 (54.1%) experienced linezolid overexposure (group B) [29/33 transiently (subgroup B1) and 4/33 persistently (subgroup B2)]. No patient experienced linezolid underexposure. Median duration of treatment for the different groups ranged between 19 and 54 days. Thrombocytopenia occurred overall in 14.8% of cases (9/61). The incidence rate of thrombocytopenia was significantly lower (P=0.012) in both group A (10.7%; 3/28) and subgroup B1 (10.3%; 3/29) than in subgroup B2 (75.0%; 3/4). Thrombocytopenic patients belonging to both group A and group B1 recovered from thrombocytopenia without the need for discontinuing therapy. Multivariate linear regression analysis revealed that thrombocytopenia was independently associated with baseline platelet count and with median linezolid trough concentrations.

CONCLUSIONS

Proactive TDM of linezolid may be beneficial either in preventing or in recovering from dose-dependent thrombocytopenia, even when treatment lasts for more than 28 days. Larger prospective studies are warranted to confirm our findings.

Impact of high plasma concentrations of linezolid in Taiwanese adult patients- therapeutic drug monitoring in improving adverse drug reactions

BACKGROUND

Previous studies have shown that the development of thrombocytopenia was associated with the elevated plasma concentration of linezolid, but little is known about the relationship between other uncommon adverse drug reactions (ADRs) and plasma concentration. The appropriate dosing adjustment has remained controversial. This prospective observational study was conducted to investigate the association between the plasma concentration of linezolid, ADRs, and clinical outcomes.

METHODS

Adult patients on linezolid treatment undergoing at least one therapeutic drug monitoring (TDM) were enrolled. The association between linezolid concentrations and ADRs was examined by multivariate Cox regression model. Predictors of linezolid concentrations was determined by linear regression model. The cut-off point of linezolid concentration and the effect of dosing adjustments based on TDM was also explored.

RESULTS

Of 50 patients enrolled in the study, plasma concentrations were 1.5-3 times higher than what was described in the prescribing information. The median minimum concentration (C_min) was significantly higher in patients with thrombocytopenia compared to patients without thrombocytopenia (13.0 vs. 7.2 μg/mL, P = 0.0273), and a higher median maximum concentration was also observed in patients with lactic acidosis (33.0 vs. 27.5 μg/mL, P = 0.0420). The C_min was elevated in patients with advanced age and severely impaired renal function. Dosing adjustment tailored by early TDM with the upper limit of C_min 9 μg/mL may improve platelet counts.

CONCLUSION

Elevated linezolid concentrations were associated with thrombocytopenia and lactic acidosis. TDM-guided dosing adjustment could be considered as a pragmatic way to mitigate thrombocytopenia.

Risk factor analysis for linezolid-associated thrombocytopenia in critically ill patients

Linezolid is an antibiotic used against gram-positive bacteria, including methicillin-resistant Staphylococcus aureus. Its primary adverse effect is haematotoxicity. The objective of this study was to analyse the risk factors for onset of thrombocytopenia in critically ill patients treated with linezolid. This was a retrospective, single-centre study of 72 patients. Platelets were measured from D0 to D20 after the start of treatment. The risk factors for thrombocytopenia were identified using a multivariate logistic regression analysis following a Monte Carlo simulation. Following ROC curve analysis, a baseline platelet count lower than 108 × 10⁹/L and a C_min higher than 4 mg/L, with respective odds ratios of 117 (95% CI [97-206]) and 3 (95% CI [1.5-6.2]) in the simulated population, were identified as risk factors. Among the source population patients combining these 2 factors, a significantly higher number developed thrombocytopenia (66.7% vs. 33.3%, p = 0.0042). A baseline platelet count lower than 108 × 10⁹/L and a C_min higher than 4 mg/L are risk factors for the onset of thrombocytopenia in critically ill patients treated with linezolid.

A retrospective cohort study to screen linezolid-induced thrombocytopenia in adult patients hospitalized in the Midwestern Region of Brazil

Background

Thrombocytopenia (TP) is the major event associated with linezolid (LZD) therapy. We investigated the incidence and risk factors for thrombocytopenia in hospitalized adults who received LZD (1200 mg/day) between 2015 and 2017. HIV-positive, death during follow-up and those with a baseline platelet count ≤100 × 10³/mm³ were excluded.

Method

TP was defined as a decrease in platelet count of ≥20% from the baseline level at the initiation of linezolid therapy and a final count of <100 × 10³/mm³. The odds ratios (OR) for thrombocytopenia were obtained using multivariate stepwise logistic regression analysis.

Main results

A total of 66 patients were included (mean age [SD] 62 [18], male gender [%], 37 [56]). LZD-associated TP was identified in 12 patients (18.2%). For TP, the adjusted OR [95% CI] of the platelet count ≤200 × 10³/mm³, serum creatinine and renal impairment at baseline were 5.66 [1.15–27.9], 4.57 [1.26–16.5] and 9.41 [1.09–80.54], respectively. Male gender and dosage per weight per day (DPWD) >20 mg/kg/day were not risk factors.

Conclusion

The results showed that the incidence of linezolid-induced thrombocytopenia was lower in patients with normal renal function and higher in those with platelet counts ≤200 × 10³/mm³ or serum creatinine >1.5 mg/dL at the start of the treatment.

Pharmacokinetics, toxicity and clinical efficacy of linezolid in Japanese pediatric patients

OBJECTIVES

The aims of the present study were (a) to evaluate the pharmacokinetics of linezolid, and (b) to assess the toxicity and clinical efficacy of linezolid in Japanese pediatric patients.

PATIENTS AND METHODS

Routine clinical data including serum linezolid total and unbound concentrations were collected from 15 pediatric patients (0-13 years old). Pharmacokinetics of linezolid was assumed to follow one-compartment with the first-order absorption model. The relationship between risk for thrombocytopenia and linezolid concentrations, and the variations in C-reactive protein (CRP) concentrations and body temperatures were evaluated as clinical efficacy assessment.

RESULTS

Body weight (WT) and maturation of body function were significant covariates for pharmacokinetics of linezolid in pediatric patients. The elimination half-life of linezolid in a pediatric patient with a WT of 9.9 kg and age of 24 months (median of this study) was 3.0 h. Thrombocytopenia was detected in three patients (21.4%), and the minimum concentrations (C_min) in these patients were significantly higher than those in patients without thrombocytopenia (P < 0.05). The CRP concentrations decreased more than 50% in all pediatric patients after the treatment with linezolid, however body temperatures at the end of treatment were higher than 37.5 °C in 6 patients (42.9%).

CONCLUSIONS

Although dose adjustment based on body size was performed for pediatric patients, thrombocytopenia was detected in 21.4% of pediatric patients, and higher C_min was associated with the risk of thrombocytopenia. These results encourage the implementation of individual dose adjustment based on linezolid serum concentrations for safe and appropriate treatment with linezolid.

Population Pharmacokinetics and Dosing Optimization of Linezolid in Pediatric Patients

Linezolid is a synthetic antibiotic very effective in the treatment of infections caused by Gram-positive pathogens. Although the clinical application of linezolid in children has increased progressively, data on linezolid pharmacokinetics in pediatric patients are very limited. The aim of this study was to develop a population pharmacokinetic model for linezolid in children and optimize the dosing strategy in order to improve therapeutic efficacy. We performed a prospective pharmacokinetic study of pediatric patients aged 0 to 12 years. The population pharmacokinetic model was developed using the NONMEM program. Goodness-of-fit plots, nonparametric bootstrap analysis, normalized prediction distribution errors, and a visual predictive check were employed to evaluate the final model. The dosing regimen was optimized based on the final model. The pharmacokinetic data from 112 pediatric patients ages 0.03 to 11.9 years were analyzed. The pharmacokinetics could best be described by a one-compartment model with first-order elimination along with body weight and the estimated glomerular filtration rate as significant covariates. Simulations demonstrated that the currently approved dosage of 10 mg/kg of body weight every 8 h (q8h) would lead to a high risk of underdosing for children in the presence of bacteria with MICs of ≥2 mg/liter. To reach the pharmacokinetic target, an elevated dosage of 15 or 20 mg/kg q8h may be required for them. The population pharmacokinetics of linezolid were characterized in pediatric patients, and simulations provide an evidence-based approach for linezolid dosage individualization.

Real-Life Frequency of New-Onset Thrombocytopenia during Linezolid Treatment

BACKGROUND

Thrombocytopenia is a well-recognized adverse effect of linezolid; however, the frequency of this adverse effect during therapy has been variable across previous studies, and the associated risk factors are unclear.

OBJECTIVES

To identify the real-life frequency of new-onset thrombocytopenia due to linezolid and to determine the associated risk factors.

METHODS

A retrospective observational cohort study was conducted among consecutive inpatients at a tertiary care hospital who received linezolid for a minimum of 5 days between January 2013 and August 2017. Data were extracted from electronic medical records obtained from a hospital database. Thrombocytopenia was defined as platelet count less than 100 × 10⁹/L or a 50% reduction from baseline (i.e., before linezolid initiation). Risk factors were identified by comparing the characteristics of patients who experienced the adverse effect during linezolid therapy with those of patients who did not experience the adverse effect. Continuous data were analyzed with the t test and categorical data with the χ² test.

RESULTS

A total of 102 patients were included (38 women, 64 men; overall mean age 50 years, standard deviation [SD] 21). The mean duration of linezolid therapy was 14 (SD 10) days. Thrombocytopenia occurred in 18 patients (17.6%). Risk factors for the development of thrombocytopenia included mean duration of therapy (22 [SD 18] days versus 12 [SD 7] days; p = 0.023), renal replacement therapy (17% versus 4%; p = 0.032), renal impairment (61% versus 32%; p = 0.021), and concomitant administration of unfractionated heparin (50% versus 21%; p = 0.013).

CONCLUSIONS

The real-life frequency of new-onset of thrombocytopenia in patients receiving linezolid for a minimum of 5 days was 17.6%. Risk factors for linezolid-induced thrombocytopenia included prolonged duration of therapy, renal impairment, and concomitant unfractionated heparin.

Linezolid-induced pancytopenia

Linezolid is a bacteriostatic antibiotic of the Oxazolidinone class; it works by inhibiting the initiation of protein synthesis on bacterial ribosomes. Due to its excellent bioavailability after oral dosing, it has become an important tool in combating multi-drug-resistant bacteria including glycopeptide-resistant enterococci and methicillin-resistant Staphylococcus aureus Side effects are multiple and potentially serious. We report the case of an 87-year-old man who developed pancytopenia secondary to a 6-week course of linezolid. Withdrawal of the antibiotic was decided as the treatment and resolution of the pancytopenia was evident within 2 weeks. Clinicians should be aware of this side effect of linezolid therapy and that weekly full blood count monitoring is paramount.

Real-Life Evidence for Tedizolid Phosphate in the Treatment of Cellulitis and Wound Infections: A Case Series

Introduction

Tedizolid phosphate 200 mg, once daily for 6 days, has recently been approved for the treatment of patients with acute bacterial skin and skin structure infections (ABSSSIs) in several countries; however, clinical experience in real-life settings is currently limited. Here, we report on the use of tedizolid with an extended treatment duration for complex and severe ABSSSIs in real-world clinical settings.

Methods

Two patients with cellulitis and two patients with surgical site infection (SSI), aged 26–60 years, were treated with tedizolid phosphate 200 mg, intravenous/oral (IV/PO) or IV only, once daily at four different institutions.

Results

Two morbidly obese patients had non-necrotizing, non-purulent severe cellulitis, which were complicated by sepsis or systemic inflammatory response syndrome plus myositis. One female patient failed on first-line empiric therapy with IV cefalotin, clindamycin and imipenem (3–4 days), and was switched to IV/PO tedizolid (7 + 5 days). One male patient received IV clindamycin plus IV/PO tedizolid (5 + 5 days), but clindamycin was discontinued on Day 3 due to an adverse event. For both patients, clinical signs and symptoms improved within 72 h, and laboratory results were normalized by Days 7 and 8, respectively. Two other patients (one obese, diabetic female with chronic hepatitis and chronic obstructive pulmonary disease) had complicated SSIs occurring 10 days after hernia repair with mesh or 3 months after spinal fusion surgery with metal implant. First patient with previous methicillin-resistant Staphylococcus aureus (MRSA) bacteremia received a 7-day tedizolid IV course empirically. The second patient with culture-confirmed MRSA infection received a 14-day IV course. Both patients responded within 72 h, and local and systemic signs normalized by end of treatment. There were no reports of thrombocytopenia.

Conclusion

Tedizolid phosphate 200 mg for 7–14 days was a favored treatment option for patients with severe/complex ABSSSIs, and was effective following previous treatment failure or in late-onset infections.

Funding

Editorial assistance and the article processing charges were funded by Bayer AG, Berlin, Germany.

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.

Thrombocytopenia with Tedizolid and Linezolid

Several studies have suggested the risk of thrombocytopenia with tedizolid, a second-in-class oxazolidinone antibiotic (approved June 2014), is less than that observed with linezolid (first-in-class oxazolidinone). Using data from the Food and Drug Administration adverse event reporting system (July 2014 through December 2016), we observed significantly increased risks of thrombocytopenia of similar magnitudes with both antibiotics: linezolid reporting odds ratio [ROR], 37.9 (95% confidence interval [CI], 20.78 to 69.17); tedizolid ROR, 34.0 (95% CI, 4.67 to 247.30).

Comparative analysis of lactic acidosis induced by linezolid and vancomycin therapy using cohort and case-control studies of incidence and associated risk factors

PURPOSE

Lactic acidosis is a rare complication of linezolid (LZD) therapy, and its incidence and risk factors remain unknown. This study aimed to compare the incidence of LZD-associated lactic acidosis (LALA) and vancomycin (VAN)-associated lactic acidosis (VALA) and investigate the risk factors for LALA.

METHODS

We performed a retrospective cohort study using propensity score-matched analyses comparing the incidence of lactic acidosis between LZD and VAN therapy. We included adult patients administered LZD or VAN between April 2014 and March 2016 and extracted patient baseline data. In a case-control study, we identified the risk factors of lactic acidosis in patients treated with LZD.

RESULTS

We identified 94 and 313 patients who were administered LZD and VAN, respectively. The incidence of lactic acidosis after LZD and VAN therapy was 10.6 and 0.3%, respectively. After propensity score-matched analyses, the incidence of lactic acidosis with LZD therapy was significantly higher than that with VAN therapy [10.0% (8/80) vs. 0% (0/80), respectively; risk difference, 0.1; 95% confidence interval (CI), 0.03-0.17; p = 0.004]. In a case-control study, 10 patients with LALA were matched to 20 non-lactic acidosis patients by age and sex. Patients with LALA were more likely to have renal insufficiency than non-lactic acidosis patients that were in the univariate analysis (odds ratio, 7.4; 95% CI, 1.0-84.4; p = 0.02).

CONCLUSIONS

This study indicates that LALA occurs more frequently than VALA does and is associated with renal insufficiency. Therefore, close monitoring of kidney function and serum lactate is recommended during LZD therapy.

Systematic Therapeutic Drug Monitoring for Linezolid: Variability and Clinical Impact

Linezolid serum trough (C_min) and peak (C_max) levels were determined prospectively in 90 patients. Adequate exposure was defined as a C_min of 2 to 8 mg/liter. Therapy was empirical (73.3%) or targeted (26.7%). Wide interindividual variability in linezolid C_min levels was recorded (0.1 to 25.2 μg/ml). Overall, 65.5% of the patients had out-of-range, 41.1% had subtherapeutic, and 24.4% had supratherapeutic trough levels. We did not find a correlation between abnormal levels and adverse events, in-hospital mortality, or overall poor outcome.

Mechanism Underlying Linezolid-induced Thrombocytopenia in a Chronic Kidney Failure Mouse Model

Objective:

To investigate the relationship between renal function and linezolid (LZD)-induced thrombocytopenia and elucidate the underlying mechanism using a chronic renal disease (CRD) mouse model.

Materials and Methods:

CRD was induced in 5-week-old male Institute of Cancer Research (ICR) mice by 5/6 nephrectomy. After this procedure, LZD (25 and 100 mg/kg) was administered intraperitoneally once every day for 28 days. Platelet counts, white blood cell (WBC) counts, and hematocrit (HCT) levels were measured every 7 days. 2-¹⁴C-thymidine (0.185 MBq) was administrated intravenously to LZD-administered mice to evaluate the thymidine uptake ability of bone marrow.

Results:

Platelet counts were significantly lower in the LZD-administered CRD group than in the LZD-nonadministered groups at 14, 21, and 28 days (P < 0.05); however, these changes were not observed in LZD-administered mice with normal renal function, regardless of the duration of LZD administration. No significant changes were observed in WBC counts or HCT levels in any LZD-administered CRD mouse. Moreover, radioactive levels in bone marrow were not significantly different in each group.

Conclusions:

These results indicate that LZD-induced decreases in platelet counts were enhanced by renal impairment in vivo, suggesting that LZD-induced thrombocytopenia is not caused by nonimmune-mediated bone marrow suppression.

Linezolid: a promising option in the treatment of Gram-positives

Linezolid, an oxazolidinone antimicrobial agent that acts by inhibiting protein synthesis in a unique fashion, is used in the treatment of community-acquired pneumonia, skin and soft-tissue infections and other infections caused by Gram-positive bacteria including VRE and methicillin-resistant staphylococci. Currently, linezolid resistance among these pathogens remains low, commonly <1.0%, although the prevalence of antibiotic resistance is increasing in many countries. Therefore, the development of resistance by clinical isolates should prompt increased attention of clinical laboratories to routinely perform linezolid susceptibility testing for this important agent and should be taken into account when considering its therapeutic use. Considering the importance of linezolid in the treatment of infections caused by Gram-positive bacteria, this review was undertaken to optimize the clinical use of this antibiotic.

Linezolid in the treatment of drug-resistant tuberculosis: the challenge of its narrow therapeutic index

INTRODUCTION

Linezolid is an oxazolidinone with potent activity against M tuberculosis, and improves culture conversion and cure rates when added to treatment regimens for drug resistant tuberculosis. However, linezolid has a narrow therapeutic window, and the optimal dosing strategy that minimizes the substantial toxicity associated with linezolid's prolonged use in tuberculosis treatment has not been determined, limiting the potential impact of this anti-mycobacterial agent.

AREAS COVERED

This paper aims to review and summarize the current knowledge on linezolid for the treatment of drug-resistant tuberculosis. The focus is on the pharmacokinetic-pharmacodynamic determinants of linezolid's efficacy and toxicity in tuberculosis, and how this relates to defining an optimal dose. Mechanisms of linezolid toxicity and resistance, and the potential role of therapeutic drug monitoring are also covered. Expert commentary: Prospective pharmacokinetic-pharmacodynamic studies are required to define optimal therapeutic targets and to inform improved linezolid dosing strategies for drug-resistant tuberculosis.