Exploring the impact of baseline platelet count on linezolid-induced thrombocytopenia: a retrospective single-center observation study

BACKGROUND

Patients treated with linezolid (LZD) frequently develop thrombocytopenia, and previous studies have identified the risk factors for this condition. However, the relationship between the development of LZD-induced thrombocytopenia and baseline platelet count has varied according to different reports.

AIM

To explore the relationship between platelet count and the development of LZD-induced thrombocytopenia.

METHOD

Patients who underwent LZD at Hokkaido University Hospital in Japan from September 2008 to March 2023 were included. We collected data on patient characteristics and platelet counts at baseline and during LZD therapy from the electronic medical records. Thrombocytopenia was defined as a decrease in platelet count by 30% or more from baseline, or a platelet level < 100,000/µL.

RESULTS

Two hundred and ninety-five patients who received LZD were included in this study, of whom 34.9% developed thrombocytopenia. In the early days of LZD treatment, the thrombocytopenia group showed a nearly 5% decrease in platelet count, while the non-thrombocytopenia group exhibited an increase of over 5%. Additionally, focusing on early onset thrombocytopenia (within 5 days), a baseline platelet count of < 150,000/µL was identified as a risk factor for early thrombocytopenia. Conversely, it was also observed that 24.7% of patients with a baseline platelet count ≥ 150,000/µL still developed early thrombocytopenia.

CONCLUSION

Our findings suggest that while a baseline platelet count of < 150,000/µL is a risk factor for the early onset of thrombocytopenia, vigilant monitoring of platelet counts by clinical pharmacists in the early stages of LZD treatment is essential, regardless of baseline platelet levels.

Population pharmacokinetics and dosage optimization of linezolid in Chinese older patients

PURPOSE

To assess the pharmacokinetics and pharmacodynamics of linezolid in a retrospective cohort of hospitalized Chinese older patients.

METHODS

Patients > 60 years of age, who received intravenous linezolid (600 mg), were included. A population pharmacokinetics (PPK) model was established using nonlinear mixed-effects modeling. The predictive performance of the final model was assessed using goodness-of-fit plots, bootstrap analyses, and visual predictive checks. Monte Carlo simulations were used to evaluate the achievement of a pharmacodynamics target for the area under the serum concentration-time curve/minimum inhibitory concentration (AUC0-24/MIC).

RESULTS

A total of 210 samples were collected from 120 patients. A one-compartment PPK model with linear elimination best predicted the linezolid plasma concentrations. Linezolid clearance (CL) was 4.22 L h-1 and volume of distribution (Vd) was 45.80 L; serum uric acid (SUA) was a significant covariate of CL.

CONCLUSION

The results of this study indicated that the standard dose was associated with a risk of overexposure in older patients, particularly those with high SUA values; these patients would benefit from a lower dose (300 mg every 12 h).

Comparison of the incidence of nausea and vomiting between linezolid and vancomycin using claims database: a retrospective cohort study

BACKGROUND

Nausea and vomiting during linezolid therapy have been reported as part of safety analyses in clinical trials. We have previously examined the incidence of vomiting during linezolid therapy (18.1%). A previous study conducted at a single hospital showed low external validity. It is necessary to verify whether these results can be reproduced using generalizable data sources.

AIM

To evaluate the incidence of nausea and vomiting during linezolid therapy compared with vancomycin using a Japanese claims database.

METHOD

Patients administered linezolid or vancomycin were selected from the database between January 2005 and June 2017. The primary endpoint was the comparison of nausea and vomiting between the linezolid and vancomycin groups. We conducted propensity score matching (PSM) to adjust for patient characteristics. To assess risk factors for nausea and vomiting, logistic regression was conducted as the secondary endpoint. We defined nausea and vomiting as the first prescription of antiemetics during linezolid or vancomycin therapy as a surrogate endpoint.

RESULTS

In total, 1215 patients were enrolled. After PSM, the number of patients in the linezolid and vancomycin groups was 241. Nausea and vomiting were observed in 11.2% and 5.0% of patients in the linezolid and vancomycin groups, respectively (p < 0.05). Linezolid administration was extracted as a risk factor for nausea and vomiting (odds ratio, 2.09; 95% confidence interval, 1.02-4.30).

CONCLUSION

This study clarified the relationship between linezolid and nausea and vomiting using a Japanese claims database. Further studies are required to elucidate the unknown mechanisms of linezolid-induced nausea and vomiting.

Towards a better detection of patients at-risk of linezolid toxicity in clinical practice: a prospective study in three Belgian hospital centers

Introduction: Linezolid is a last-resort antibiotic for infections caused by multidrug-resistant microorganisms. It is widely used for off-label indications and for longer than recommended treatment durations, exposing patients at higher risk of adverse drug reactions (ADRs), notably thrombocytopenia. This study aimed to investigate ADR incidence and risk factors, identify thrombocytopenia-related trough levels based on treatment duration, and evaluate the performance of predictive scores for ADR development. Methods: Adult in- and outpatients undergoing linezolid therapy were enrolled in three hospitals and ADRs and linezolid trough levels prospectively monitored over time. A population pharmacokinetic (pop-PK model) was used to estimate trough levels for blood samples collected at varying times. Results: A multivariate analysis based on 63 treatments identified treatment duration ≥10 days and trough levels >8 mg/L as independent risk factors of developing thrombocytopenia, with high trough values correlated with impaired renal function. Five patients treated for >28 days did not develop thrombocytopenia but maintained trough values in the target range (<8 mg/L). The Buzelé predictive score, which combines an age-adjusted Charlson comorbidity index with treatment duration, demonstrated 77% specificity and 67% sensitivity to predict the risk of ADR. Conclusion: Our work supports the necessity of establishing guidelines for dose adjustment in patients with renal insufficiency and the systematic use of TDM in patients at-risk in order to keep trough values ≤8 mg/L. The Buzelé predictive score (if ≥7) may help to detect these at-risk patients, and pop-PK models can estimate trough levels based on plasma samples collected at varying times, reducing the logistical burden of TDM in clinical practice.

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.

Rifampicin reduces plasma concentration of linezolid in patients with infective endocarditis

BACKGROUND

Linezolid in combination with rifampicin has been used in treatment of infective endocarditis especially for patients infected with staphylococci.

OBJECTIVES

Because rifampicin has been reported to reduce the plasma concentration of linezolid, the present study aimed to characterize the population pharmacokinetics of linezolid for the purpose of quantifying an effect of rifampicin cotreatment. In addition, the possibility of compensation by dosage adjustments was evaluated.

PATIENTS AND METHODS

Pharmacokinetic measurements were performed in 62 patients treated with linezolid for left-sided infective endocarditis in the Partial Oral Endocarditis Treatment (POET) trial. Fifteen patients were cotreated with rifampicin. A total of 437 linezolid plasma concentrations were obtained. The pharmacokinetic data were adequately described by a one-compartment model with first-order absorption and first-order elimination.

RESULTS

We demonstrated a substantial increase of linezolid clearance by 150% (95% CI: 78%-251%), when combined with rifampicin. The final model was evaluated by goodness-of-fit plots showing an acceptable fit, and a visual predictive check validated the model. Model-based dosing simulations showed that rifampicin cotreatment decreased the PTA of linezolid from 94.3% to 34.9% and from 52.7% to 3.5% for MICs of 2 mg/L and 4 mg/L, respectively.

CONCLUSIONS

A substantial interaction between linezolid and rifampicin was detected in patients with infective endocarditis, and the interaction was stronger than previously reported. Model-based simulations showed that increasing the linezolid dose might compensate without increasing the risk of adverse effects to the same degree.

Linezolid dose adjustment according to therapeutic drug monitoring helps reach the goal concentration in severe patients, and the oldest seniors benefit more

BACKGROUND

The elderly with severe infection increased dramatically in intensive care unit (ICU). Proper antimicrobial therapy help improve the prognosis. Linezolid, as an antimicrobial drug, is commonly utilized to treat patients infected with methicillin-resistant S. aureus and vancomycin-resistant enterococci. Clinical evidence suggests elderly patients prone to linezolid overexposure. Here, we describe the results of three years' linezolid adjustment experiences according to therapeutic drug monitoring (TDM), especially in the oldest old.

METHODS

Linezolid therapeutic drug monitoring data were collected between January 2020 and November 2022 from patients who were admitted to ICU and treated with linezolid. All the patients started with a dosage of 600 mg, twice daily. The first TMD was carried out ten minutes before the seventh administration. The dosage adjustment was determined by the doctor according to the first TMD and patients' condition, and the repeated TDM was conducted as required. The dosage adjustment in different age group was recorded. Laboratory data were compared between the old and the oldest old. The high mortality risk of the oldest old was also explored.

RESULTS

Data of 556 linezolid TDM from 330 patients were collected. Among which, 31.6%, 54.8%, and 75% of patients had supra-therapeutic linezolid trough concentrations at the first TDM assessment in different age group, leading to the dosage adjustment rate of 31.0%, 40.3%, 68.8% respectively. The linezolid dosage adjustments according to TDM help to reach therapeutic concentration. The oldest old was in high risk of linezolid overexposure with lowercreatinine clearance. The norepinephrine maximum dosage but not linezolid Cmin was associated with 28-day mortality in the oldest old.

CONCLUSIONS

Elderly patients with linezolid conventional 600 mg twice-daily dose might be at a high risk of overexposure, especially in the oldest old. The linezolid dosage adjustments according to TDM help reach the therapeutic concentration. The high mortality of the oldest old was not related with initial linezolid overexposure.

Infant Exposure to Antituberculosis Drugs via Breast Milk and Assessment of Potential Adverse Effects in Breastfed Infants: Critical Review of Data

Infants of mothers treated for tuberculosis might be exposed to drugs via breast milk. The existing information on the exposure of breastfed infants lacks a critical review of the published data. We aimed to evaluate the quality of the existing data on antituberculosis (anti-TB) drug concentrations in the plasma and milk as a methodologically sound basis for the potential risk of breastfeeding under therapy. We performed a systematic search in PubMed for bedaquiline, clofazimine, cycloserine/terizidone, levofloxacin, linezolid, pretomanid/pa824, pyrazinamide, streptomycin, ethambutol, rifampicin and isoniazid, supplemented with update references found in LactMed^®. We calculated the external infant exposure (EID) for each drug and compared it with the recommended WHO dose for infants (relative external infant dose) and assessed their potential to elicit adverse effects in the breastfed infant. Breast milk concentration data were mainly not satisfactory to properly estimate the EID. Most of the studies suffer from limitations in the sample collection, quantity, timing and study design. Infant plasma concentrations are extremely scarce and very little data exist documenting the clinical outcome in exposed infants. Concerns for potential adverse effects in breastfed infants could be ruled out for bedaquiline, cycloserine/terizidone, linezolid and pyrazinamide. Adequate studies should be performed covering the scenario in treated mothers, breast milk and infants.

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 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.

Parametric Population Pharmacokinetics of Linezolid: A Systematic Review

BACKGROUND

Linezolid is often used for infections caused by drug-resistant Gram-positive bacteria. Recent studies suggest that large between-subject variability (BSV) and within-subject variability could alter drug pharmacokinetics (PK) during linezolid therapy due to pathophysiological changes.

OBJECTIVE

This review synthesized information on linezolid population PK studies and summarized the significant covariates that influence linezolid PK.

METHODS

A literature search was performed using PubMed, Web of Science, and Embase from their inception to 30 September 2021. Published studies were included if they contained data analyzing linezolid PK parameters in humans using a population approach with a nonlinear mixed-effects model.

RESULTS

Twenty-five studies conducted in adults and five in pediatrics were included. One- and two-compartment models were the commonly used structural models for linezolid. Body size (weight, lean body weight, and body surface area), creatinine clearance (CLcr), and age significantly influenced linezolid PK. The median clearance (CL) values (ranges) in infants [0.128 L/h/kg (0.121-0.135)] and children [0.107 L/h/kg (0.088-0.151)] were higher than in adults [0.098 L/h/kg (0.044-0.237)]. For patients with severe renal impairment (CLcr ≤ 30 mL/min), the CL was 37.2% (15.2-55.3%) lower than in patients with normal renal function.

CONCLUSION

The optimal linezolid dosage should be adjusted based on the patient's body size, renal function, and age. More studies are needed to explore the exact mechanism of linezolid elimination and evaluate the PK characteristics in pediatric patients.

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.

Efficient simulation of clinical target response surfaces

Simulation of combination therapies is challenging due to computational complexity. Either a simple model is used to simulate the response for many combinations of concentration to generate a response surface but parameter variability and uncertainty are neglected and the concentrations are constant—the link to the doses to be administered is difficult to make—or a population pharmacokinetic/pharmacodynamic model is used to predict the response to combination therapy in a clinical trial taking into account the time‐varying concentration profile, interindividual variability (IIV), and parameter uncertainty but simulations are limited to only a few selected doses. We devised new algorithms to efficiently search for the combination doses that achieve a predefined efficacy target while taking into account the IIV and parameter uncertainty. The result of this method is a response surface of confidence levels, indicating for all dose combinations the likelihood of reaching the specified efficacy target. We highlight the importance to simulate across a population rather than focus on an individual. Finally, we provide examples of potential applications, such as informing experimental design.

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.

Therapeutic Drug Monitoring of Antibiotics in the Elderly: A Narrative Review

PURPOSE

Antibiotic dosing adaptation in elderly patients is frequently complicated by age-related changes affecting the processes of drug absorption, distribution, metabolism, and/or elimination. These events eventually result in treatment failure and/or development of drug-related toxicity. Therapeutic drug monitoring (TDM) can prevent suboptimal antibiotic exposure in adult patients regardless of age. However, little data are available concerning the specific role of TDM in the elderly.

METHODS

This review is based on a PubMed search of the literature published in the English language. The search involved TDM studies of antibiotics in the elderly performed between 1990 and 2021. Additional studies were identified from the reference lists of the retrieved articles. Studies dealing with population pharmacokinetic modeling were not considered.

RESULTS

Only a few studies, mainly retrospective and with observational design, have specifically dealt with appropriate antibiotic dosing in the elderly based on TDM. Nevertheless, some clinical situations in which the selection of optimal antibiotic dosing in the elderly was successfully guided by TDM were identified.

CONCLUSIONS

Elderly patients are at an increased risk of bacterial infections and inadequate drug dosing compared to younger patients. Therefore, the availability of TDM services can improve the appropriateness of antibiotic prescriptions in this population.

Population pharmacokinetics and target attainment analysis of linezolid in multidrug-resistant tuberculosis patients

AIM

This study investigates the pharmacokinetic/pharmacodynamic (PK/PD) target attainment of linezolid in patients infected with multidrug-resistant (MDR) tuberculosis (TB).

METHODS

A pharmacometric model was developed including 244 timed linezolid concentration samples from 39 patients employing NONMEM 7.4. The probability of target attainment (PTA, PK/PD target: unbound (f) area-under-the-concentration-time-curve (AUC)/minimal inhibitory concentration (MIC) of 119) as well as a region-specific cumulative fraction of response (CFR) were estimated for different dosing regimens.

RESULTS

A one-compartment model with linear elimination with a clearance (CL) of 7.69 L/h (interindividual variability 34.1%), a volume of distribution (Vd) of 45.2 L and an absorption constant (KA) of 0.679 h^-1 (interoccasion variability 143.7%) allometric scaled by weight best described the PK of linezolid. The PTA at an MIC of 0.5 mg/L was 55% or 97% if patients receiving 300 or 600 mg twice daily, respectively. CFRs varied greatly among populations and geographic regions. A desirable global CFR of ≥90% was achieved if linezolid was administered at a dose of 600 mg twice daily but not at a dose of 300 mg twice daily.

CONCLUSION

This study showed that a dose of 300 mg twice daily of linezolid might not be sufficient to treat MDR-TB patients from a PK/PD perspective. Thus, it might be recommendable to start with a higher dose of 600 mg twice daily to ensure PK/PD target attainment. Hereby, therapeutic drug monitoring and MIC determination should be performed to control PK/PD target attainment as linezolid shows high variability in its PK in the TB population.

Investigation of the risk factors of vomiting during linezolid therapy: a retrospective observational study

PURPOSE

Some clinical studies have reported the occurrence of nausea and vomiting with linezolid (LZD) administration. However, no studies have evaluated nausea and vomiting as primary endpoints. In a previous study, we noted a possible relationship between LZD and vomiting, but risk factors were not identified. Therefore, the aim of the present study was to identify them.

METHODS

Patients who received LZD 600 mg twice daily at Hokkaido University Hospital from September 2008 to April 2019 were enrolled in this retrospective observational study. Patient characteristics, concomitant medications, laboratory data, and the occurrence of vomiting were obtained from electronic medical records. Logistic regression analysis was performed to identify risk factors for vomiting, including age, sex, body weight, concomitant medications, and surgeries.

RESULTS

A total of 496 patients were included in this study, of which 90 experienced vomiting. By multivariate logistic regression analysis, female sex (adjusted odds ratio [aOR], 2.69; 95% confidence interval [CI], 1.62-4.47), ≥ 10 days of LZD administration (aOR, 2.57; CI, 1.46-4.50), and hyponatraemia (aOR, 2.96; CI, 1.72-5.10) were identified as independent risk factors for vomiting; administration of serotonergic agents (aOR, 0.23; CI, 0.07-0.82) was negatively associated.

CONCLUSIONS

This study is the first to successfully identify risk factors for LZD-induced vomiting. Careful monitoring of patients with these risk factors may lead to safer and sustainable LZD administration.

Effect of renal function on the risk of thrombocytopenia in patients receiving linezolid therapy: a systematic review and meta-analysis

Aims

The association of renal function and linezolid‐induced thrombocytopaenia (LIT) remains controversial. We performed a meta‐analysis to determine whether impaired renal function is associated with an increased LIT risk.

Methods

We conducted a systematic search of PubMed, EMBASE and the Cochrane Library from inception to February 2021 for eligible studies evaluating the relationship between renal function and LIT. Indicators of renal function included renal impairment (RI), severe RI, haemodialysis status, creatinine clearance rate (Ccr) and estimated glomerular filtration rate (eGFR). Unadjusted and adjusted estimates and 95% confidence intervals (CIs) were calculated separately using a random‐effect model.

Results

A total of 24 studies with 3580 patients were included in the meta‐analysis. RI patients had an increased LIT risk compared to non‐RI patients in both the unadjusted (OR 3.54; 95% CI 2.27, 5.54; I² = 77.7%) and adjusted analyses (OR 2.51; 95% CI 1.82, 3.45; I² = 17.9%). This association persisted in the subset of studies involving only patients receiving a fixed conventional dose (600 mg every 12 h) and other subgroup analyses by ethnicity, sample size and study quality. Moreover, the LIT risk was significantly higher in patients with severe RI and haemodialysis than in patients without severe RI and haemodialysis. The eGFR and Ccr were significantly lower in LIT patients than in non‐LIT patients.

Conclusions

Impaired renal function is associated with an increased risk of LIT. A reduced linezolid dose may be considered in RI patients at a low risk of treatment failure, ideally guided by therapeutic drug monitoring.

Dosage Individualization of Linezolid: Precision Dosing of Linezolid To Optimize Efficacy and Minimize Toxicity

The high interindividual variability in the pharmacokinetics (PK) of linezolid has been described, which results in an unacceptably high proportion of patients with either suboptimal or potentially toxic concentrations following the administration of a fixed regimen. The aim of this study was to develop a population pharmacokinetic model of linezolid and use this to build and validate alogorithms for individualized dosing. A retrospective pharmacokinetic analysis was performed using data from 338 hospitalized patients (65.4% male, 65.5 [±14.6] years) who underwent routine therapeutic drug monitoring for linezolid. Linezolid concentrations were analyzed by using high-performance liquid chromatography. Population pharmacokinetic modeling was performed using a nonparametric methodology with Pmetrics, and Monte Carlo simulations were employed to calculate the 100% time >MIC after the administration of a fixed regimen of 600 mg administered every 12 h (q12h) intravenously (i.v.). The dose of linezolid needed to achieve a PTA ≥ 90% for all susceptible isolates classified according to EUCAST was estimated to be as high as 2,400 mg q12h, which is 4 times higher than the maximum licensed linezolid dose. The final PK model was then used to construct software for dosage individualization, and the performance of the software was assessed using 10 new patients not used to construct the original population PK model. A three-compartment model with an absorptive compartment with zero-order i.v. input and first-order clearance from the central compartment best described the data. The dose optimization software tracked patients with a high degree of accuracy. The software may be a clinically useful tool to adjust linezolid dosages in real time to achieve prespecified drug exposure targets. A further prospective study is needed to examine the potential clinical utility of individualized therapy.

Population Pharmacokinetics and Dosage Optimization of Linezolid in Critically Ill Pediatric Patients

Linezolid is an oxazolidinone antibiotic exhibiting efficacy against multidrug-resistant (MDR) Gram-positive-related infections. However, its population pharmacokinetic (PopPK) profile in Chinese critically ill children has not been characterized. Optimal dosing regimens should be established according to the PopPK/pharmacodynamic(PD) properties of linezolid in the specific population. This work aims to describe the pharmacokinetic (PK) properties of linezolid, assess the factors affecting interpatient variability, and establish an optimized regimen for children in pediatric intensive care unit (PICU). A single-center, prospective, open-labeled PK study was performed. Ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was applied to measure the plasma levels during linezolid treatment. PopPK analysis was conducted using Phoenix NLME software. Sixty-three critically ill pediatric patients were included. The data showed good fit for a two-compartment model with linear elimination. Body weight and aspartate aminotransferase (AST) were the most significant covariates explaining variabilities in linezolid PK for the pediatric population. Therapeutic target was defined as the ratio of the area under drug plasma concentration-time curve over 24 h to minimum inhibitory concentration (AUC/MIC) of >80. 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 (>96%) for 10 mg/kg every 8 h at MIC≤1 mg/L, it was lower than 70% at MIC>1 mg/L. Thus, the dosing regimen required adjustment. When the dosing regimen was adjusted to 15 mg/kg every 6 h, the PTA increased from 63.6% to 94.6% at MIC=2 mg/L, thereby indicating higher treatment success. Children with AST of >40 U/L had significant higher AUC than those with AST of ≤40 U/L (205.45 vs. 159.96). Therefore, dosage adjustment was required according to the AST levels. The PopPK characteristics of linezolid in critically ill children were evaluated, and an optimal dosage regimen was constructed based on developmental PopPK/PD model and simulation. (This study has been registered in the Chinese Clinical Trial Registry under no. ChiCTR1900021386.).

External Evaluation of Population Pharmacokinetics and Pharmacodynamics in Linezolid-Induced Thrombocytopenia: The Transferability of Published Models to Different Hospitalized Patients

BACKGROUND

The objective of this study was to perform an external evaluation of published linezolid population pharmacokinetic and pharmacodynamic models, to evaluate the predictive performance using an independent data set. Another aim was to offer an elegant environment for display and simulation of both the concentration and platelet count after linezolid administration.

METHODS

We performed a systematic literature search in PubMed for all studies evaluating the population pharmacokinetic and pharmacodynamic parameters of linezolid in patients and selected the models to be used for the external validation. The bias of predictions was visually evaluated by plotting prediction errors (PEs) and relative PEs. The precision of prediction was evaluated by calculating the mean absolute error (MAE), root mean squared error (RMSE), and mean relative error (MRE).

RESULTS

Three articles (models A, B, and C) provided linezolid-induced platelet dynamic models using population pharmacokinetic and pharmacodynamic modeling approaches. The PE and relative PE of both linezolid concentrations and platelet counts for models A and C showed similar predictive distributions. With respect to the prediction accuracy of total linezolid concentration, the MAE, RMSE, and MRE of population prediction values for model C was the smallest. The comparison of the MAE, RMSE, and MRE of patient-individual prediction values for the 3 pharmacodynamic models revealed no large differences.

CONCLUSIONS

We confirmed the transferability of published population pharmacokinetic and pharmacodynamic models and showed that they were suitable for extrapolation to other hospitals and/or patients. This study also introduced application software based on model C for the therapeutic drug monitoring of linezolid.

Supra-therapeutic Linezolid Trough Concentrations in Elderly Patients: A Call for Action?

BACKGROUND AND OBJECTIVE

According to the drug label, linezolid dosage adjustments are not needed in geriatric patients. Nevertheless, clinical evidence suggests that elderly patients may benefit from the use of reduced linezolid doses to limit drug overexposure. Here, we aimed to describe the results of the last 5 years of therapeutic drug monitoring of linezolid in our institution with a special focus on elderly patients.

METHODS

Linezolid therapeutic drug monitoring requests collected between January 2016 and June 2020 were considered. Linezolid trough concentrations were considered both as a continuous variable and as a categorical variable, clustering data according to the therapeutic range proposed by available literature (< 2, 2-8, and > 8 mg/L, respectively). Patients' age and sex were considered as categorical variables. Comparisons of linezolid trough concentrations between groups of patients stratified according to age were performed using an analysis of variance; comparisons in the frequency distributions were performed using the chi-squared test.

RESULTS

From 2016 to 2020, we collected 3250 linezolid TDM requests. A highly significant, progressive increment in the linezolid trough concentrations was observed moving from patients aged < 50 years (5.8 ± 5.6 mg/L) to those aged > 90 years (16.6 ± 10.0 mg/L), with an overall increment of 30% per decade of age. Nearly 30%, 50%, and 65% of patients aged < 65 years, 65-80 years, and > 80 years, respectively, had supra-therapeutic linezolid trough concentrations at the first therapeutic drug monitoring assessment. This trend did not change significantly moving from 2016 to 2020.

CONCLUSIONS

Elderly patients given linezolid at the conventional 600-mg twice-daily dose might be at a high risk of being overexposed to treatment, eventually increasing their risk to experience drug-related hematological toxicity. Reduced linezolid dosing schemes should be potentially considered in elderly patients at a low risk of treatment failure, ideally guided by therapeutic drug monitoring.

Linezolid Dosing in Patients With Liver Cirrhosis: Standard Dosing Risk Toxicity

BACKGROUND

Limited data regarding altered linezolid pharmacokinetics in patients with liver cirrhosis are available. The objective of this study was to evaluate the pharmacokinetics, efficacy and safety of linezolid in cirrhotic patients.

METHODS

A case-control 1:1 study of patients undergoing linezolid therapeutic drug monitoring was conducted between January 2015 and June 2017. Cases with liver cirrhosis were matched with controls by age, body weight, comorbidities, renal function, and intensive care unit (ICU) admission.

RESULTS

Fifty-two patients were included, 26 in each group. Patients with Child-Pugh Scores A, B, and C were 1 (3.8%), 13 (50.0%), and 12 (46.2%), respectively. Cases had higher median linezolid trough plasma concentrations than controls [20.6 (17.4) versus 2.7 (11.3); P < 0.001)] and more frequently achieved an optimal pharmacodynamic index [26 (100%) versus 16 (61.5%); P = 0.002]. In addition, potentially toxic concentrations and treatment discontinuation due to overexposure and hematological toxicity were also more frequently seen in cirrhotic patients. Overall clinical cure rate was high (67.4%), and in-hospital mortality was 28.8%. No differences in clinical outcomes were observed between both groups.

CONCLUSIONS

Linezolid showed a high clinical cure rate. Nevertheless, plasma concentrations and treatment discontinuation due to hematological toxicity were higher in cirrhotic patients. Liver cirrhosis may influence linezolid pharmacokinetics and question the use of standard doses. Therapeutic drug monitoring of linezolid would be valuable in these patients.

Variable linezolid exposure and response and the role of therapeutic drug monitoring: Case series

Two patients with normal renal function, yet each showed unexpected, supra- and subtherapeutic linezolid plasma concentrations resulting in toxicity and ineffective therapy, respectively. TDM helps to early identify and correct such excursions.

Pharmacokinetic evaluation of linezolid administered intravenously in obese patients with pneumonia

OBJECTIVES

Altered linezolid pharmacokinetics (PK) in obese individuals has been hypothesized in previous studies. However, specific dosing recommendations for this population are still lacking. The main goal of this study was to evaluate PK/pharmacodynamic (PKPD) target attainment when using a 600 mg intravenous q12h linezolid dose against MRSA in obese patients with pneumonia.

METHODS

Fifteen obese pneumonia patients with a confirmed or suspected MRSA involvement treated with 600 mg of intravenous linezolid q12h were studied for 3 days. Population PK modelling was used to characterize the PK variability and to screen for influential patient characteristics. Monte Carlo simulations were carried out to investigate the PTA and time to target attainment for linezolid dosing against MRSA.

RESULTS

A two-compartment model with linear elimination adequately described the data. Body weight and age both have a significant effect on linezolid clearance. Simulations demonstrate that the probability of attaining PKPD targets is low. Moreover, the PTA decreases with weight, and increases with age. Standard linezolid dosing in obese pneumonia patients with MRSA (MICs of 1-4 mg/L) leads to unacceptably low (near zero to 60%) PTA for patients <65 years old.

CONCLUSIONS

Standard linezolid dosing is likely to provide insufficient target attainment against MRSA in obese patients. Body weight and especially age are important characteristics to be considered when administering linezolid to treat MRSA infections.

Fourteen-Day Bactericidal Activity, Safety, and Pharmacokinetics of Linezolid in Adults with Drug-Sensitive Pulmonary Tuberculosis

Linezolid is increasingly used for the treatment of tuberculosis resistant to first-line agents, but the most effective dosing strategy is yet unknown. From November 2014 to November 2016, we randomized 114 drug-sensitive treatment-naive pulmonary tuberculosis patients from Cape Town, South Africa, to one of six 14-day treatment arms containing linezolid at 300 mg once daily (QD), 300 mg twice daily (BD), 600 mg QD, 600 mg BD, 1,200 mg QD, 1,200 mg three times per week (TIW), or a combination of isoniazid, rifampin, pyrazinamide, and ethambutol. Sixteen-hour sputum samples were collected overnight, and bactericidal activity was characterized by the daily percentage change in time to positivity (TTP) and the daily rate of change in log₁₀(CFU). We also assessed the safety and pharmacokinetics of the study treatments. We found that bactericidal activity increased with increasing doses of linezolid. Based on the daily percentage change in TTP, activity was highest for 1,200 mg QD (4.5%; 95% Bayesian confidence interval [BCI], 3.3 to 5.6), followed by 600 mg BD (4.1%; BCI, 2.5 to 5.7), 600 mg QD (4.1%; BCI, 2.9 to 5.3), 300 mg BD (3.3%; BCI, 1.9 to 4.7), 300 mg QD (2.3%; BCI, 1.1 to 3.5), and 1,200 mg TIW (2.2%; BCI, 1.1 to 3.3). Similar results were seen with bactericidal activity characterized by the daily rate of change in CFU count. Antimycobacterial activity correlated positively with plasma drug exposure and percentage time over MIC. There were no unexpected adverse events. All linezolid doses showed bactericidal activity. For the same total daily dose, once-daily dosing proved to be at least as effective as a divided twice-daily dose. An intermittent dosing regimen, with 1,200 mg given three times weekly, showed the least activity. (This study has been registered at ClinicalTrials.gov under identifier NCT02279875.).

Considerations for the optimal management of antibiotic therapy in elderly patients

OBJECTIVES

To maximise efficacy and minimise toxicity, special considerations are required for antibiotic prescription in elderly patients. This review aims to provide practical suggestions for the optimal management of antibiotic therapy in elderly patients.

METHODS

This was a narrative review. A literature search of published articles in the last 15 years on antibiotics and elderly patients was performed using the Cochrane Library and PubMed electronic databases. The three priority areas were identified: (i) pharmacokinetics/pharmacodynamics (PK/PD) for optimising dosage regimens and route of administration; (ii) antibiotic dosages in some special subpopulations; and (iii) treatment considerations relating to different antibiotic classes and their adverse events.

RESULTS

Clinicians should understand the altered PK/PD of drugs in this population owing to co-morbid conditions and normal physiological changes associated with ageing. The body of evidence justifies the need for individualised dose selection, especially in patients with impaired renal and liver function. Clinicians should be aware of the major drug-drug interactions commonly observed in the elderly as well as potential side effects.

CONCLUSION

Antibiotic therapy in the elderly requires a comprehensive approach, including strategies to improve appropriate antibiotic prescribing, limit their use for uncomplicated infections and ensure the attainment of an optimal PK/PD target. To this purpose, further studies involving the elderly are needed to better understand the PK of antibiotics. Moreover, it is necessary to assess the role therapeutic drug monitoring in guiding antibiotic therapy in elderly patients in order to evaluate its impact on clinical outcome.

Reappraisal of Linezolid Dosing in Renal Impairment To Improve Safety

Linezolid is administered as a fixed dose to all patients despite evidence of increased exposure and myelosuppression in renal impairment. The objectives of these studies were to assess the risk of thrombocytopenia with standard-dose linezolid in renal impairment and to identify an alternate dosing strategy. In study 1, data from adult patients receiving linezolid for ≥10 days were retrospectively reviewed to determine the frequency of thrombocytopenia in patients with and without renal impairment. Time-to-event analyses were performed using Cox proportional-hazards models. In study 2, population pharmacokinetic modeling was employed to build covariate-structured models using an independent data set of linezolid concentrations obtained during routine therapeutic drug monitoring (TDM). Monte Carlo simulations were performed to identify linezolid dosing regimens that maximized attainment of therapeutic trough concentrations (2 to 8 mg/liter) across various renal-function groups. Toxicity analysis (study 1) included 341 patients, 133 (39.0%) with renal impairment. Thrombocytopenia occurred more frequently among patients with renal impairment (42.9% versus 16.8%; P < 0.001), and renal impairment was independently associated with this toxicity in multivariable analysis (adjusted hazard ratio [aHR], 2.37; 95% confidence interval [CI], 1.52 to 3.68). Pharmacokinetic analyses (study 2) included 1,309 linezolid concentrations from 603 adult patients. Age, body surface area, and estimated glomerular filtration rate (eGFR) were identified as covariates of linezolid clearance. Linezolid dose reductions improved the probability of achieving optimal exposures in simulated patients with eGFR values of <60 ml/min. Thrombocytopenia occurs more frequently in patients with renal impairment receiving standard linezolid doses. Linezolid dose reduction and trough-based TDM are predicted to mitigate this treatment-limiting toxicity.

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.

Linezolid Pharmacokinetics in South African Patients with Drug-Resistant Tuberculosis and a High Prevalence of HIV Coinfection

The World Health Organization (WHO) recently recommended that linezolid be prioritized in treatment regimens for drug-resistant tuberculosis (TB), but there are limited data on its pharmacokinetics (PK) in patients with this disease. We conducted an observational study to explore covariate effects on linezolid PK and to estimate the probability of PK/pharmacodynamic target attainment in South African patients with drug-resistant TB. Consecutive adults on linezolid-based regimens were recruited in Cape Town and underwent intensive PK sampling at steady state. Noncompartmental analysis was performed. Thirty participants were included: 15 HIV positive, 26 on the initial dose of 600 mg daily, and 4 participants on 300 mg daily after dose reduction for linezolid-related toxicity. There was a negative correlation between body weight and exposure, with 17.4% (95% confidence interval [CI], 0.1 to 31.7) decrease in area under the concentration-time curve from 0 to 24 h (AUC_0-24) per 10-kg weight increment after adjustment for other covariates. Age was an independent predictor of trough concentration, with an estimated 43.4% (95% CI, 5.9 to 94.2) increase per 10-year increment in age. The standard 600-mg dose achieved the efficacy target of free AUC/MIC of >119 at wild-type MIC values (≤0.5 mg/liter), but the probability of target attainment dropped to 61.5% (95% CI, 40.6 to 79.8) at the critical concentration of 1 mg/liter. When dosed at 600 mg daily, trough concentrations were above the toxicity threshold of 2 mg/liter in 57.7% (95% CI, 36.9 to 76.6). This confirms the narrow therapeutic index of linezolid, and alternative dosing strategies should be explored.

Population Pharmacokinetics of Intravenous Linezolid in Premature Infants

BACKGROUND

The emergence of coagulase-negative staphylococci with reduced vancomycin susceptibility in some neonatal intensive care units has resulted in an increase of linezolid use. Linezolid pharmacokinetics (PK) and safety in premature infants still need to be better established.

METHODS

This was a retrospective PK study. All infants who received intravenous linezolid and had linezolid plasma concentrations per standard of care were included. Linezolid concentrations were measured by high performance liquid chromatography. A population PK model was developed using nonlinear mixed effects modeling. Optimal dosing was determined based on achievement of the surrogate pharmacodynamics target for efficacy: a ratio of the area under the concentration-time curve to minimum inhibitory concentration >80. We assessed the occurrence of thrombocytopenia and lactic acidosis in relation with drug exposure.

RESULTS

A total of 78 plasma concentrations were collected from 26 infants, with a median postnatal age (PNA) of 24 days (8-88) and weight of 1423 g (810-3256). A 1-compartment model described linezolid data well. The final model included PNA and weight on clearance and weight on volume of distribution. Considering an MIC90 of 1 mg/L, all infants reached an area under the concentration-time curve/minimum inhibitory concentration > 80. Although thrombocytopenia and hyperlactatemia occurred frequently, they were not sustained and were not considered related to linezolid.

CONCLUSION

and was well tolerated in critically ill premature infants. PNA was the main determinant of clearance.

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.

Linezolid as treatment for pulmonary Mycobacterium avium disease

Objectives

To identify the pharmacokinetic/pharmacodynamic parameters and exposures of linezolid in the treatment of pulmonary Mycobacterium avium complex (MAC) disease.

Methods

Human-derived monocytes infected with MAC were inoculated into hollow-fibre systems for dose-effect and dose-scheduling studies. We mimicked linezolid concentration-time profiles achieved in adult human lungs treated for 28 days. Sampling to confirm that the intended linezolid pharmacokinetics had been achieved, and for enumeration of MAC colony-forming units, was performed based on repetitive sampling from each system over the 28 days. We then performed 10 000 patient Monte Carlo simulations to identify doses associated with optimal effect in the clinic.

Results

Linezolid achieved a hitherto unprecedented feat of at least 1.0 log10 cfu/mL reduction. Efficacy was most closely linked to the AUC0-24/MIC ratio. The AUC0-24/MIC ratio associated with no change in bacterial burden or bacteriostasis was 7.82, while that associated with 1.0 log10 cfu/mL kill was 42.06. The clinical dose of 600 mg/day achieved or exceeded the bacteriostasis exposure in 98.73% of patients. The proportion of 10 000 patients treated with the standard 1200 mg/day who achieved the exposure for 1.0 log10 cfu/mL kill was 70.64%, but was 90% for 1800 mg/day. The proposed MIC breakpoint for linezolid is 16 mg/L, with which 49%-80% of clinical isolates would be considered resistant.

Conclusions

Linezolid is associated with a bactericidal effect in pulmonary MAC that is greater than that seen with other recommended drugs. However, because of the MIC distribution, doses that would optimize the bactericidal effect would be associated with a high adverse event rate.

A programme to create short-course chemotherapy for pulmonary Mycobacterium avium disease based on pharmacokinetics/pharmacodynamics and mathematical forecasting

Objectives

Pulmonary Mycobacterium avium complex (MAC) prevalence is on the rise worldwide. The average therapy duration is 1.5 years, which is associated with poor cure rates. Our objective was to develop a programme to design a combination therapy regimen for pulmonary MAC to be administered for 6 months or less with efficacy in > 90% of patients.

Methods

We performed a literature search for the following MeSH headings 'Mycobacterium avium' AND 'pharmacokinetics/pharmacodynamics' in PubMed up to 2016. The findings were then used to identify steps in the programme to design new regimens with faster microbial kill rates than the current standard regimen.

Results

First, we designed a strategy for rapid in vitro screening of all antibiotic classes for repurposing against pulmonary MAC. Secondly, we identified and compared maximal microbial kill rates (Emax), and optimal exposures of eight different antibiotics. These studies had all been performed in the hollow-fibre system model of pulmonary MAC (HFS-MAC). Thirdly, all drugs with a high Emax at clinically achievable optimal exposures will be chosen, and exposures associated with synergy or additivity for two/three drugs identified based on Bliss independence. Fourthly, the time-kill slopes and resistance suppression of the chosen combinations will be compared with those of standard combination therapy in the HFS-MAC. Finally, we will identify the clinical doses best able to achieve synergistic or additive combination exposures by taking into account pharmacokinetic variability.

Conclusions

Our stepwise pharmacokinetics/pharmacodynamics approach provides a scientific rationale and a strategy for achieving short-course chemotherapy for pulmonary MAC disease within a few years.

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.

Linezolid Dose That Maximizes Sterilizing Effect While Minimizing Toxicity and Resistance Emergence for Tuberculosis

Linezolid has an excellent sterilizing effect in tuberculosis patients but high adverse event rates. The dose that would maximize efficacy and minimize toxicity is unknown. We performed linezolid dose-effect and dose-scheduling studies in the hollow fiber system model of tuberculosis (HFS-TB) for sterilizing effect. HFS-TB units were treated with several doses to mimic human-like linezolid intrapulmonary pharmacokinetics and repetitively sampled for drug concentration, total bacterial burden, linezolid-resistant subpopulations, and RNA sequencing over 2 months. Linezolid-resistant isolates underwent whole-genome sequencing. The expression of genes encoding efflux pumps in the first 1 to 2 weeks revealed the same exposure-response patterns as the linezolid-resistant subpopulation. Linezolid-resistant isolates from the 2nd month of therapy revealed mutations in several efflux pump/transporter genes and a LuxR-family transcriptional regulator. Linezolid sterilizing effect was linked to the ratio of unbound 0- to 24-h area under the concentration-time curve (AUC_0–24) to MIC. Optimal microbial kill was achieved at an AUC_0–24/MIC ratio of 119. The optimal sterilizing effect dose for clinical use was identified using Monte Carlo simulations. Clinical doses of 300 and 600 mg/day (or double the dose every other day) achieved this target in 87% and >99% of 10,000 patients, respectively. The susceptibility breakpoint identified was 2 mg/liter. The simulations identified that a 300-mg/day dose did not achieve AUC_0–24s associated with linezolid toxicity, while 600 mg/day achieved those AUC_0–24s in <20% of subjects. The linezolid dose of 300 mg/day performed well and should be compared to 600 mg/day or 1,200 mg every other day in clinical trials.

Population pharmacokinetics and pharmacodynamics of linezolid-induced thrombocytopenia in hospitalized patients

AIMS

Thrombocytopenia is among the most important adverse effects of linezolid treatment. Linezolid-induced thrombocytopenia incidence varies considerably but has been associated with impaired renal function. We investigated the pharmacodynamic mechanism (myelosuppression or enhanced platelet destruction) and the role of impaired renal function (RF) in the development of thrombocytopenia.

METHODS

The pharmacokinetics of linezolid were described with a two-compartment distribution model with first-order absorption and elimination. RF was calculated using the expected creatinine clearance. The decrease platelets by linezolid exposure was assumed to occur by one of two mechanisms: inhibition of the formation of platelets (PDI) or stimulation of the elimination (PDS) of platelets.

RESULTS

About 50% of elimination was found to be explained by renal clearance (normal RF). The population mean estimated plasma protein binding of linezolid was 18% [95% confidence interval (CI) 16%, 20%] and was independent of the observed concentrations. The estimated mixture model fraction of patients with a platelet count decreased due to PDI was 0.97 (95% CI 0.87, 1.00), so the fraction due to PDS was 0.03. RF had no influence on linezolid pharmacodynamics.

CONCLUSION

We have described the influence of weight, renal function, age and plasma protein binding on the pharmacokinetics of linezolid. This combined pharmacokinetic, pharmacodynamic and turnover model identified that the most common mechanism of thrombocytopenia associated with linezolid is PDI. Impaired RF increases thrombocytopenia by a pharmacokinetic mechanism. The linezolid dose should be reduced in RF.

The epidemiology, pathogenesis, transmission, diagnosis, and management of multidrug-resistant, extensively drug-resistant, and incurable tuberculosis

Global tuberculosis incidence has declined marginally over the past decade, and tuberculosis remains out of control in several parts of the world including Africa and Asia. Although tuberculosis control has been effective in some regions of the world, these gains are threatened by the increasing burden of multidrug-resistant (MDR) and extensively drug-resistant (XDR) tuberculosis. XDR tuberculosis has evolved in several tuberculosis-endemic countries to drug-incurable or programmatically incurable tuberculosis (totally drug-resistant tuberculosis). This poses several challenges similar to those encountered in the pre-chemotherapy era, including the inability to cure tuberculosis, high mortality, and the need for alternative methods to prevent disease transmission. This phenomenon mirrors the worldwide increase in antimicrobial resistance and the emergence of other MDR pathogens, such as malaria, HIV, and Gram-negative bacteria. MDR and XDR tuberculosis are associated with high morbidity and substantial mortality, are a threat to health-care workers, prohibitively expensive to treat, and are therefore a serious public health problem. In this Commission, we examine several aspects of drug-resistant tuberculosis. The traditional view that acquired resistance to antituberculous drugs is driven by poor compliance and programmatic failure is now being questioned, and several lines of evidence suggest that alternative mechanisms-including pharmacokinetic variability, induction of efflux pumps that transport the drug out of cells, and suboptimal drug penetration into tuberculosis lesions-are likely crucial to the pathogenesis of drug-resistant tuberculosis. These factors have implications for the design of new interventions, drug delivery and dosing mechanisms, and public health policy. We discuss epidemiology and transmission dynamics, including new insights into the fundamental biology of transmission, and we review the utility of newer diagnostic tools, including molecular tests and next-generation whole-genome sequencing, and their potential for clinical effectiveness. Relevant research priorities are highlighted, including optimal medical and surgical management, the role of newer and repurposed drugs (including bedaquiline, delamanid, and linezolid), pharmacokinetic and pharmacodynamic considerations, preventive strategies (such as prophylaxis in MDR and XDR contacts), palliative and patient-orientated care aspects, and medicolegal and ethical issues.

Therapeutic drug management of linezolid: a missed opportunity for clinicians?

Some studies have shown that adjustments to the linezolid dose guided by therapeutic drug monitoring (TDM) can reduce interindividual variability in drug exposure and improve linezolid tolerability. In this study, 6 years of linezolid TDM, a diagnostic service for our hospital and others in the Milan (Italy) area, is described. Samples were collected immediately before the morning dose intake (trough concentrations) in steady-state conditions. Linezolid concentrations were quantified by a validated high-performance liquid chromatography (HPLC) method. Four hundred linezolid trough concentrations from 220 patients were collected. A 20-fold variability in linezolid levels was observed. Positive and significant correlations between linezolid trough concentrations and patient age (r = 0.325, P <0.01) or serum creatinine (r = 0.511, P <0.01) were found. A progressive increase in linezolid concentrations with time was observed in a subgroup of patients with more than one TDM assessment. Elderly patients, especially those aged >80 years and with impaired renal function, are at a higher risk of overexposure to linezolid. Despite the observed progressive increase in linezolid concentrations over time, most physicians did not change the drug dose according to the TDM results, even in the presence of frank overexposure to linezolid.

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.

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.

Risk factors associated with high linezolid trough plasma concentrations

AIM

The major concern of linezolid is the adverse events. High linezolid trough serum concentration (Cmin) has been associated with toxicity. The aim of this study was to analyze factors associated with high Cmin.

METHODS

Main clinical characteristics of 104 patients treated with 600 mg/12 hours of linezolid were retrospectively reviewed. Samples were obtained just before the next dose after at least three doses and within the first 8 days of treatment. High Cmin was considered when it was >8 mg/L. Univariate and multivariate analysis were performed.

RESULTS

34.6% patients had a Cmin >8 mg/L, and they were older and had more frequently an estimated glomerular filtration by MDRD <40 mL/min. There were more patients co-treated with rifampin in the group with low Cmin. The only factor independently associated with Cmin >8 was the renal function. Patients with an eGF < 40 mL/min had significantly higher Cmin than those with eGF > 80 mL/min (OR: 4.273) and there was a trend towards a high Cmin in patients with eGF between 40-80 mL/min (OR: 2.109).

CONCLUSIONS

High Cmin were frequent, especially in patients with MDRD <40 mL/min. Therapeutic drug monitoring could be useful to avoid toxicity in patients with renal dysfunction.