Pharmacokinetic evaluation of linezolid administered intravenously in obese patients with pneumonia

Evaluation and application of population pharmacokinetic models for optimising linezolid treatment in non-adherence multidrug-resistant tuberculosis patients

BACKGROUND

Population pharmacokinetic (popPK) models can optimise linezolid dosage regimens in patients with multidrug-resistant tuberculosis (MDR-TB); however, unknown cross-centre precision and poor adherence remain problematic. This study aimed to assess the predictive ability of published models and use the most suitable model to optimise dosage regimens and manage compliance.

METHODS

One hundred fifty-eight linezolid plasma concentrations from 27 patients with MDR-TB were used to assess the predictive performance of published models. Prediction-based metrics and simulation-based visual predictive checks were conducted to evaluate predictive ability. Individualised remedial dosing regimens for various delayed scenarios were optimised using the most suitable model and Monte Carlo simulations. The influence of covariates, scheduled dosing intervals, and patient compliance were assessed.

RESULTS

Seven popPK models were identified. Body weight and creatinine clearance were the most frequently identified covariates influencing linezolid clearance. The model with the best performance had a median prediction error (PE%) of -1.62 %, median absolute PE of 29.50 %, and percentages of PE within 20 % (F20, 36.97 %) and 30 % (F30, 51.26 %). Monte Carlo simulations indicated that a twice-daily 300 mg linezolid dose may be more efficient than 600 mg once daily. For the 'typical' patient treated with 300 mg twice daily, half the dosage should be taken after a delay of ≥ 3 h.

CONCLUSIONS

Monte Carlo simulations based on popPK models can propose remedial regimens for delayed doses of linezolid in patients with MDR-TB. Model-based compliance management patterns are useful for balancing efficacy, adverse reactions, and resistance suppression.

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).

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.

Risk factors for thrombocytopenia in patients receiving linezolid therapy: a systematic review and meta-analysis

PURPOSE

The incidence of linezolid-induced thrombocytopenia (LIT) has been reported to vary widely across studies. We performed a meta-analysis to identify the risk factors for thrombocytopenia among patients who received linezolid treatment.

METHODS

The PubMed, Embase and Cochrane Library databases were searched from inception to November 2022 to identify eligible studies. Data on the potential predictors of incidence in LIT were pooled using a random effects model. Sensitivity analyses were performed to determine the robustness of the results when significant heterogeneity was observed.

RESULTS

Forty observational studies involving 6454 patients treated with linezolid were included in the analysis. LIT was estimated to occur in 37% of patients. The following important factors were associated with the incidence of LIT: advanced age, body mass index, concurrent renal impairment or liver disease, abnormal laboratory parameters (including white blood cell count, serum creatinine, baseline platelet count, albumin, creatinine clearance rate, and estimated glomerular filtration rate), treatment duration and renal replacement therapy.

CONCLUSIONS

A variety of risk factors related to the occurrence of LIT were revealed in our analysis. Early identification of these factors could help patients improve clinical outcomes.

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.

Developmental Pharmacokinetics of Antibiotics Used in Neonatal ICU: Focus on Preterm Infants

Neonatal Infections are among the most common reasons for admission to the intensive care unit. Neonatal sepsis (NS) significantly contributes to mortality rates. Empiric antibiotic therapy of NS recommended by current international guidelines includes benzylpenicillin, ampicillin/amoxicillin, and aminoglycosides (gentamicin). The rise of antibacterial resistance precipitates the growth of the use of antibiotics of the Watch (second, third, and fourth generations of cephalosporines, carbapenems, macrolides, glycopeptides, rifamycins, fluoroquinolones) and Reserve groups (fifth generation of cephalosporines, oxazolidinones, lipoglycopeptides, fosfomycin), which are associated with a less clinical experience and higher risks of toxic reactions. A proper dosing regimen is essential for effective and safe antibiotic therapy, but its choice in neonates is complicated with high variability in the maturation of organ systems affecting drug absorption, distribution, metabolism, and excretion. Changes in antibiotic pharmacokinetic parameters result in altered efficacy and safety. Population pharmacokinetics can help to prognosis outcomes of antibiotic therapy, but it should be considered that the neonatal population is heterogeneous, and this heterogeneity is mainly determined by gestational and postnatal age. Preterm neonates are common in clinical practice, and due to the different physiology compared to the full terms, constitute a specific neonatal subpopulation. The objective of this review is to summarize the evidence about the developmental changes (specific for preterm and full-term infants, separately) of pharmacokinetic parameters of antibiotics used in neonatal intensive care units.

Comprehensive guidance for antibiotic dosing in obese adults: 2022 update

Drug dosing in obese patients continues to be challenging due to a lack of high-quality evidence to guide dosing recommendations. We first published guidance for antibiotic dosing in obese adults in 2017, in which we critically reviewed articles identified from a broad search strategy to develop dosing recommendations for 35 antimicrobials. In this updated narrative review, we searched Pubmed, Web of Science, and the Cochrane Library using Medical Subject Headings including anti-infectives, specific generic antimicrobial names, obese, pharmacokinetics, and others. We reviewed 393 articles, cross-referenced select cited references, and when applicable, referenced drug databases, package inserts, and clinical trial data to update dosing recommendations for 41 antimicrobials. Most included articles were pharmacokinetic studies, other less frequently included articles were clinical studies (mostly small, retrospective), case reports, and very rarely, guidelines. Pharmacokinetic changes are frequently reported, can be variable, and sometimes conflicting in this population, and do not always translate to a documented difference in clinical outcomes, yet are used to inform dosing strategies. Extended infusions, high doses, and therapeutic drug monitoring remain important strategies to optimize dosing in this population. Additional studies are needed to clinically validate proposed dosing strategies, clarify optimal body size descriptors, dosing weight scalars, and estimation method of renal function in obese patients.

Linezolid pharmacokinetics: a systematic review for the best clinical practice

OBJECTIVES

To summarize the pharmacokinetics of linezolid to optimize the dosing regimen in special populations.

METHODS

A literature search was performed in three largest medical databases, including Embase, Scopus, and PubMed. The main applied keywords were linezolid and pharmacokinetics. Of 3663 retrieved publications in the English language, 35 original research articles, clinical studies, and case reports about linezolid pharmacokinetics in different populations such as pregnant women, pediatrics, elderly subjects, obese people, individuals with organ dysfunction, and critically ill patients were included. RESULTS AND CONCLUSION: Dose adjustment is not currently recommended for linezolid in patients with mild to moderate renal or hepatic impairment, older adults, and pregnant women. Although dose adjustment is not recommended in patients with severe renal or hepatic impairment, it should be considered that these patients are more vulnerable to linezolid adverse effects and drug interactions. In pediatrics, reducing the linezolid dosing interval to 8 h is suggested. Despite the lack of sufficient information in obese individuals, dosing based on body weight or use of higher dose seems to be justifiable to prevent sub-therapeutic concentrations. Although dose adjustment of linezolid is not recommended in critically ill patients, administration of linezolid as continuous intravenous infusion is suggested in this population. Blood level monitoring should be considered in populations that are vulnerable to linezolid underexposure (such as critically ill patients with augmented renal clearance, pediatrics, overweight, and obese patients) or overexposure (such as elderly, patients with hepatic and renal impairment). To assess the efficacy and safety of linezolid, the area under the concentration-time curve over 24 h to minimum inhibitory concentration (AUC0-24 h/MIC) equal to 80-120, percentage of time above the MIC ≥ 85%, and serum trough concentration between 2 and 7 mg/L are suggested.

Evaluating linezolid dose regimens against methicillin-resistant Staphylococcus aureus based on renal function in populations with different body weight

WHAT IS KNOWN AND OBJECTIVE

Linezolid is an alternative first-line agent for MRSA pneumonia. This study assessed whether dose adjustments of linezolid against methicillin-resistant Staphylococcus aureus (MRSA) infections were needed based on renal function in populations with different body weight.

METHODS

Monte Carlo simulations were conducted to evaluate renal function in relation to the probability of target attainment (PTA) in three population groups with different body weight. Area under the concentration time curve (AUC)/ minimum inhibitory concentration (MIC) ratio and percentage of time above the MIC (%T > MIC) were regarded as pharmacokinetic/pharmacodynamic targets. The PTA and cumulative fractions of response (CFR) were calculated to assess the efficacy. Regarding safety, trough plasma concentration (C_min ) > 8 mg/L was used as target for toxicity.

RESULTS AND DISCUSSION

Using AUC/MIC >100 as the target pharmacodynamic (PD) index, the CFR of linezolid at the standard dose (600 mg every 12 h [q12h]) were 57.01%, 93.22%, and 99.93% in patients with normal renal function, patients with renal dysfunction and low body weight patients with renal dysfunction, respectively. Using 100%T > MIC as the target PD index, all the CFR of three population groups were more than 90% at the standard dose. The percentages of C_min  > 8 mg/L at the standard dose of linezolid were 24.16%, 53.24%, and 90.10% in three population groups on day 7.

WHAT IS NEW AND CONCLUSION

The risk of thrombocytopenia of linezolid was extremely higher in low body weight patients with renal impairment when receiving standard linezolid dose compared with patients with normal renal function. 450 mg q12h and 300 mg q12h might be effective and safe against MRSA infection in patients with renal dysfunction and low body weight patients with renal dysfunction, respectively.

Bioequivalence of Two Linezolid Tablets Under Fed and Fasting Conditions in Healthy Chinese Individuals

Linezolid, an oxazolidinone antibacterial agent with several formulations, has been widely used for over 20 years. This study aimed to compare the bioequivalence, pharmacokinetics, and safety of test and reference linezolid tablets after a single oral dose under fasting/fed conditions. In this open-label, randomized, two-period, crossover, bioequivalence study, 48 healthy volunteers were enrolled equally to fasting or fed groups to receive one 600-mg test or reference linezolid tablet in each period. Pharmacokinetic parameters were calculated using noncompartmental methods. Adverse events (AEs) were recorded to assess safety. The geometric mean terminal half-lives of test and reference formulations were 3.8 and 3.6 hours, respectively, under both fasting and fed conditions. The median time to reach the maximum observed concentration was 1.0 hour (both formulations) in the fasting group, and 2.0 hours (test formulation) and 2.5 hours (reference formulation) in the fed group. No substantial differences were observed in the area under plasma concentration-time curve (AUC) from time 0 to the last sampling time (AUC_0-t ) and the maximum observed concentration (C_max ) between formulations. Geometric least square mean ratios for C_max , AUC_0-t , and AUC from time 0 to infinity were approximately 100%, and the corresponding 90% confidence intervals for bioequivalence were within 80%-125%. Ten participants reported 11 AEs; AEs were mild, except for one pregnancy event with an outcome of induced absorption. Bioequivalence between the two linezolid formulations was demonstrated under fasting and fed conditions, and a similar safety profile was observed among healthy Chinese volunteers.

Expert consensus statement on therapeutic drug monitoring and individualization of linezolid

Linezolid is an oxazolidinone antibacterial drug, and its therapeutic drug monitoring and individualized treatment have been challenged since its approval. With the in-depth clinical research of linezolid, we have changed our attitude toward its therapeutic drug monitoring and our view of individualized treatment. On the basis of summarizing the existing clinical studies, and based on the practical experience of each expert in their respective professional fields, we have formed this expert consensus. Our team of specialists is a multidisciplinary team that includes pharmacotherapists, clinical pharmacology specialists, critical care medicine specialists, respiratory specialists, infectious disease specialists, emergency medicine specialists and more. We are committed to the safe and effective use of linezolid in patients in need, and the promotion of its therapeutic drug monitoring.

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.

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.

Safety and efficacy of omadacycline by BMI categories and diabetes history in two Phase III randomized studies of patients with acute bacterial skin and skin structure infections

OBJECTIVES

The objectives of this post-hoc analysis were to examine the safety and efficacy of omadacycline by BMI categories and diabetes history in adults with acute bacterial skin and skin structure infections (ABSSSI) from two pivotal Phase III studies.

PATIENTS AND METHODS

OASIS-1 (ClinicalTrials.gov identifier NCT02378480): patients were randomized 1:1 to IV omadacycline or linezolid for 7-14 days, with optional transition to oral medication. OASIS-2 (ClinicalTrials.gov identifier NCT02877927): patients received once-daily oral omadacycline or twice-daily oral linezolid for 7-14 days. Early clinical response (ECR) was defined as ≥20% reduction in lesion size 48-72 h after the first dose. Clinical success at post-treatment evaluation (PTE; 7-14 days after the last dose) was defined as symptom resolution such that antibacterial therapy was unnecessary. Safety was assessed by treatment-emergent adverse events and laboratory measures. Between-treatment comparisons were made with regard to WHO BMI categories and diabetes history.

RESULTS

Patients were evenly distributed among healthy weight, overweight and obese groups. Clinical success for omadacycline-treated patients at ECR and PTE was similar across BMI categories. Outcomes by diabetes status were similar in omadacycline- and linezolid-treated patients: at ECR, clinical success rates were lower for those with diabetes; at PTE, clinical success was similar between treatment groups regardless of diabetes history. The safety of omadacycline and linezolid was largely similar across BMI groups and by diabetes history.

CONCLUSIONS

Omadacycline efficacy in patients with higher BMI and in patients with diabetes was consistent with results from two pivotal Phase III ABSSSI trials. Fixed-dose omadacycline is an appropriate treatment for ABSSSI in adults regardless of BMI.

Evaluation of Linezolid Pharmacokinetics in Critically Ill Obese Patients with Severe Skin and Soft Tissue Infections

Linezolid standard dosing is fixed at 600 mg every 12 h (q12h) for adults. Literature suggests critically ill, obese patients require higher doses. The study aim is 2-fold: (i) to describe linezolid pharmacokinetics (PK), and (ii) to evaluate if PK/pharmacodynamic (PD) target attainment is achieved with standard dosing in critically ill, obese patients with severe skin and soft tissue infections (SSTIs). Adult patients with a body mass index (BMI) of ≥30 kg/m² and receiving intravenous (i.v.) linezolid from August 2018 to April 2019 were eligible for consent in this prospective study. Severe SSTIs were defined as necrotizing fasciitis, myonecrosis, or SSTI with sepsis syndrome. Four blood samples were collected at steady state at 1, 3, 5 h postinfusion and as a trough. Target attainment was defined as achieving area under the concentration-time curve from 0 to 24 h to MIC (AUC_0-24h/MIC) of ≥100 h*mg/liter. Monte Carlo simulations were used to determine the probability of target attainment (PTA). Eleven patients were included in the study. The median BMI was 45.7 kg/m², and median total body weight (TBW) was 136.0 kg. Seven patients received standard linezolid doses, and four received 600 mg q8h. A one-compartment model described linezolid PK. Based on AUC_0-24h/MIC targets, for noncirrhotic patients at 140 kg, the PTA with standard linezolid doses was 100%, 98.8%, 34.1%, and 0% for MICs of 0.5, 1, 2, and 4 mg/liter, respectively. In conclusion, target attainment of ≥90% is not achieved with standard linezolid doses for noncirrhotic patients ≥140 kg with MICs of ≥2 mg/liter. This study adds to accumulating evidence that standard linezolid doses may not be adequate for all patients.

Linezolid Concentrations in Plasma and Subcutaneous Tissue are Reduced in Obese Patients, Resulting in a Higher Risk of Underdosing in Critically Ill Patients: A Controlled Clinical Pharmacokinetic Study

Background: Linezolid is used for the treatment of soft tissue infections in critically ill patients. However, data for characterizing the pharmacokinetics (PK) and assessing whether effective concentrations are reached at the target site are lacking. We hypothesized that current dosing regimens do not lead to effective concentrations in the plasma and interstitial fluid (ISF) of subcutaneous tissue in obese patients. Methods: As a controlled clinical model, critically ill obese and non-obese patients undergoing intra-abdominal surgery received 600 mg linezolid as a single infusion. Concentrations in the plasma and microdialysate from the ISF of subcutaneous tissue were determined up to 8 h after dosing. Pharmacokinetic analysis was performed by non-compartmental methods. As a therapeutic target, we used fAUC/MIC > 80. Results: Fifteen obese (BMI: 48.7 ± 11.2 kg/m²) and 15 non-obese (23.9 ± 2.1 kg/m²) patients were analyzed. AUC_0–8 in ISF decreased by −1.69 mg*h/L (95% CI: −2.59 to −0.79, p < 0.001) for every 10 kg increase in weight. PK in obese patients were characterized by lower maximal plasma concentrations (median 3.8 vs. 8.3 mg/L, p < 0.001) and a higher volume of distribution (41.0 vs. 30.8 L, p < 0.001), and the therapeutic target was not reached for MIC ≥ 1 mg/L in ISF and ≥ 2 mg/L in plasma. Conclusions: Increasing the weight led to a decrease of linezolid concentrations in the plasma and subcutaneous tissue. The current dosing regimen does not seem to produce sufficient concentrations to kill bacteria with MIC ≥ 2 mg/L, especially as empirical antimicrobial therapy in critically ill obese patients.

Does the conventional dosage of linezolid necessitate therapeutic drug monitoring?-Experience from a prospective observational study

Background

The objectives of the present prospective observational study conducted in patients receiving conventional dosage of linezolid was to define the pharmacodynamic range of linezolid exposure, to assess the inter-individual variability in linezolid concentrations, and to define if therapeutic drug monitoring (TDM) of linezolid may be necessary for Chinese population.

Methods

Patients included in this study underwent linezolid TDM trough concentration (C_min) during treatment with a standard regimen in the period between January 2019 and October 2019. Linezolid C_min was analyzed with high-performance liquid chromatography (HPLC) method. Logistic regression was used to define the desired range of linezolid C_min. Linear regression and univariate logistic regression analysis were carried out to investigate variables associated with inappropriate linezolid plasma exposure.

Results

A total of 84 patients who had 153 linezolid C_min assessed were included in the study. Median linezolid C_min was 3.43 mg/L (IQR 1.59–5.93). The estimated probability of thrombocytopenia was 50% in the presence of C_min of 7.85 mg/L. Approximately 57.52% (88/153) of the samples fell within the desired range of linezolid C_min (2–8 mg/L) while 31.37% (48/153) experienced underexposure, and overexposure occurred in 11.11% (17/153) of the patients. No significant linear relationships between either body weight or estimated creatinine clearance (CrCL) and C_min were detected. Estimated CrCL ≥100 mL/min was significantly associated with linezolid underexposure (OR 4.121; 95% CI, 1.945–8.731; P<0.001). Estimated CrCL ≤40 mL/min was significantly associated with linezolid overexposure (OR 3.761; 95% CI, 1.324–10.681; P=0.013).

Conclusions

Our results suggest that the pharmacodynamic range of linezolid C_min can be defined as 2–8 mg/L for the Chinese population. Renal function partially accounts for the inter-interindividual variability of exposure. The application of TDM might be especially valuable in optimizing linezolid exposure in the majority of patients to avoid therapeutic failure and/or dose-dependent adverse reactions.