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

WHAT IS KNOWN AND OBJECTIVE

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

METHODS

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

RESULTS AND DISCUSSION

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

WHAT IS NEW AND CONCLUSION

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

Risk of serotonin syndrome in acutely ill patients receiving linezolid and opioids concomitantly: a retrospective cohort study

INTRODUCTION

Linezolid is an oxazolidinone antibiotic with a reversible, non-selective, monoamine oxidase inhibitory effect. Combining linezolid with serotonergic agents may increase serotonin syndrome (SS) risk.Linezolid is recommended in patients with suspected or confirmed resistant Gram-positive bacterial infections, especially if vancomycin cannot be used. However, it is unclear whether co-administration of linezolid with opioids increases the risk of serotonin syndrome.

RESEARCH OBJECTIVE

To establish whether combining linezolid with opioids will increase the incidence of SS in acutely ill patients.

METHODS

This was a retrospective observational study. All adult patients who were admitted and received linezolid between March and September 2020 were included in the study. The primary outcome was the prevalence of SS, as defined by Hunter's criteria.

RESULTS

The study included 106 patients, most whom were males (91.5%). More than half of the cohort (56.6%) received a concomitant opioid agent. Morphine and fentanyl were the most prescribed opioids (37.7% and 34%, respectively). Among patients who received opioids, only one patient (1.6%) had spontaneous clonus. However, this patient developed spontaneous clonus post cardiac arrest, which made an association with the linezolid-opioids combination less likely.

CONCLUSION

In this study, the incidence of SS was low in acutely ill patients who received concomitant linezolid and opioids. However, larger prospective studies are required to confirm this finding.

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.

Intensified tuberculosis treatment to reduce the mortality of HIV-infected and uninfected patients with tuberculosis meningitis (INTENSE-TBM): study protocol for a phase III randomized controlled trial

Background

Tuberculous meningitis (TBM) is the most lethal and disabling form of tuberculosis (TB), particularly in sub-Saharan Africa. Current anti-TB treatment is poorly effective since TBM mortality reaches 40% in HIV-negative patients and up to 70% in HIV-co-infected patients. To reduce TBM-induced morbidity and mortality, the INTENSE-TBM trial evaluates two interventions in both HIV-infected and uninfected patients: an anti-TB treatment intensification using oral high-dose rifampicin (35 mg/kg daily) and linezolid (1200 mg daily and then 600 mg daily) during the first 8 weeks of the anti-TB treatment and the use of adjunctive aspirin (200 mg daily).

Methods

This is a randomized controlled, phase III, multicenter, 2 × 2 factorial plan superiority trial. The trial has four arms, combining the two experimental treatments (intensified TBM regimen and aspirin) with the two reference treatments (WHO standard TB treatment and placebo), and is open-label for anti-TB treatment and double-blind placebo-controlled for aspirin treatment. This trial is conducted in adults or adolescents of age ≥15 years with TBM defined as “definite,” “probable,” or “possible” using Tuberculosis Meningitis International Research Consortium criteria, in four African countries: Ivory Coast, Madagascar, Uganda, and South Africa. The primary outcome is all-cause death between inclusion and week 40.

Discussion

The INTENSE-TBM trial represents a key opportunity to enhance TBM treatment with widely available existing drugs notably in high-incidence settings of both TB and HIV. The trial design is pragmatic and the results will permit early and effective applications in TBM patient care, in both HIV and TB high-incidence countries.

Trial registration

ClinicalTrials.gov NCT04145258. Registered on October 30, 2019.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13063-022-06772-1.

Therapeutic drug monitoring status of four common antibiotics: vancomycin, meropenem, linezolid and teicoplanin

Accurate therapeutic drug monitoring (TDM) of vancomycin, meropenem, linezolid and teicoplanin are conducive to developing optimal therapeutic regimes for patients. However, the measurement status of those drugs in different laboratories has not been reported. In this study, four samples including two frozen plasma samples and two lyophilized plasma samples were measured by over 35 laboratories across China. The inter- and intra-laboratory %CV, biases (%) of laboratories and intra- and inter-measurement-system %CV were calculated and analyzed. The short-term stability and homogeneity of those drugs in samples were studied. The results of frozen and lyophilized samples were also compared to determine whether there were significant differences in their matrix effects on various measurement systems. Results showed most laboratories' intra-laboratory %CVs were less than 9% for all drugs, and the mean inter-laboratory %CVs were 18.4%, 86.4%, 19.1% and 37.1% for vancomycin, meropenem, linezolid and teicoplanin measurements, respectively. For vancomycin, the intra-measurement %CV of commercial measurement systems was found to be smaller than that of other measurement systems. For meropenem, linezolid and teicoplanin, the agreement among laboratories using self-developed methods (Liquid chromatography-mass spectrometry [LC-MS] or high-performance liquid chromatography [HPLC]) was not satisfactory as most intra-measurement system CVs% were over 20%. Drugs in lyophilized samples were found to be more stable than in frozen samples, and no obvious differences in matrix effects were found for those two kinds of processed samples on most measurement systems. In conclusion, this study depicted the measurement status of those drugs in clinical laboratories, and found the lyophilized samples were more suitable EQA material for those drugs.

Trends of Vancomycin-Resistant Enterococcus Infections in Cancer Patients

Objective Vancomycin-resistant Enterococcus (VRE) is an important cause of infection in immunocompromised populations. In Pakistan, very limited data are available regarding Enterococcus infection and its outcomes. We conducted this study to evaluate the trends including risk factors, treatment options, and outcomes of infections due to vancomycin-resistant enterococci in cancer patients in Pakistan. Methods We conducted a retrospective observational study. We extracted data from medical records of our center over a period of seven years. All admitted cancer patients with any vancomycin-resistant Enterococcus positive culture were included. The following parameters were evaluated: age, gender, type of cancer, febrile neutropenia, prior antibiotics, admission, comorbidities, system-wise infections (including bacteremia, catheter-related infection, pneumonia, urinary tract infections, intra-abdominal infection, bone and joint infections, skin and skin structure infections), intensive care unit admission, and 30-day all-cause mortality. Frequencies of infections, mortality, and drug susceptibility were evaluated over the course of seven years. Results Risk factors for enterococcal infection included prior exposure of piperacillin/tazobactam (n=209, 86.7%), meropenem (n=132, 54.8%), vancomycin (n=126, 52.3%), metronidazole (n=67, 27.8%), prior admission for more than 48 hours (n=198, 82.2%), and comorbidities (n=76, 31.5%), with acute kidney injury being most common (n=72, 95%) followed by diabetes mellitus (n=70, 92.1%). Precursor B cell acute lymphoblastic leukemia (pre-B ALL) was the most common malignancy in which infection occurred (n=54, 38.3%). Among patients who developed infection, 46% (n=111) had febrile neutropenia. Enterococcus species caused infection in 61% (n=147) and Enterococcus faecium in 39% (n=94). Bacteremia occurred in 45.2% (n=109) patients followed by urinary tract and intra-abdominal infection; 45.6% (n=110) patients were admitted to ICU, and 30-day all-cause mortality was 44.8% (n=108). Linezolid sensitivity was 100%. The total number of enterococci infections decreased over seven years. Frequency of E. species infection, bacteremia, intra-abdominal, skin-related infections, and recurrent infection also decreased, but the frequency of E. facium infections, ICU admission, and 30-day all-cause mortality was increased. Conclusion VRE infections have become less frequent but more severe in recent years with increase in mortality. Prior use of antibiotics (including piperacillin/tazobactam, vancomycin, carbapenems, and metronidazole), diagnosis of hematological malignancy, febrile neutropenia, diabetes mellitus, and renal failure are the risk factors for VRE infection. Bacteremia was the most common infection with high mortality rate. All strains remain sensitive to linezolid. Patients with these risk factors should be worked up for VRE and can be treated with linezolid empirically.

Low-Dose Linezolid for Treatment of Patients With Multidrug-Resistant Tuberculosis

Background

Linezolid has been prioritized for treating multidrug-resistant tuberculosis (MDR TB), but toxicity limits its use. We report treatment outcomes for MDR TB patients in California who received standard-dose linezolid vs those who switched to low-dose.

Methods

We include culture-positive MDR TB cases treated with linezolid and receiving California MDR TB Service consultation during 2009-2016. Demographic, clinical, and laboratory data are analyzed using univariate analysis to compare patients who received linezolid of different dosing strategies. Analysis end points are linezolid treatment duration (measure of tolerability), treatment success (completion or cure), and adverse events (AEs).

Results

Sixty-nine of 194 (36%) MDR TB patients met inclusion criteria. While all patients began linezolid treatment at 600 mg daily, 39 (57%) continued at this dosage (standard-dose), and 30 (43%) switched to 300 mg daily (29%) or intermittent dosing (14%) (low dose). Patients on standard-dose linezolid were treated for 240 days, compared with 535 for those on low-dose (P < .0001). Sixty-three patients (91%) achieved treatment success, 2 (2.9%) died, 1 (1.5%) failed treatment, 1 (1.5%) stopped treatment due to side effects, and 2 (2.9%) were lost or moved. Treatment success was higher (P = .03) in the low-dose group. Sixty-two patients experienced ≥1 hematologic (71%) or neurologic (65%) AE. Those on low-dose linezolid experienced significantly (P = .03) fewer AEs per linezolid-month after switching (0.32 vs 0.10).

Conclusions

Patients who switched to low dose tolerated linezolid longer with better treatment outcomes and fewer recurring AEs.

Linezolid-Induced Pancytopenia in Patients Using Dapagliflozin: A Case Series

Background

Linezolid is classed as oxazolidinone antibiotics which can be used to treat severe infections caused by vancomycin-resistant Enterococcus faecium, hospital-acquired pneumonia caused by Staphylococcus aureus, complicated skin, and uncomplicated skin structure infections (SSSIs) caused by methicillin-susceptible S. aureus or Streptococcus pyogenes, and community-acquired pneumonia caused by Streptococcus pneumoniae. However, many studies have suggested it can also cause thrombocytopenia and pancytopenia.

Patients and Methods

We report on three patients with linezolid-pancytopenia. Patients in cases 1 and 2 were diagnosed with heart failure with preserved ejection fraction (HFpEF) and were both administered with dapagliflozin, one of the sodium-dependent glucose transporters 2 inhibitors (SHLT-2i).

Results

Two patients were diagnosed with type 2 diabetes, pneumonia, and hyponatremia. Severe myelosuppression occurred in both patients, with a severe decrease in leukocytes and platelets and a moderate decrease in hemoglobin, who eventually passed away despite the discontinuation of linezolid and adopting appropriate treatment measures. The patient in case 3 was diagnosed with pneumonia, type 2 diabetes, and sequelae of cerebral thrombosis. After twelve days of treatment, the patient developed moderate thrombocytopenia and anemia. She recovered without any additional treatment after the discontinuation of linezolid.

Conclusion

In this case series, two patients with irreversible myelosuppression were treated with both linezolid and SGLT-2i, and one diabetic patient with single linezolid use presented with reversible pancytopenia, suggesting that SGLT-2i may exacerbate myelosuppression of linezolid. Linezolid should be used with caution in infectious patients with a history of SGLT-2i. We will conduct relevant animal experiments to clarify the interaction between the two drugs.

Oral Bacteria Dysbiosis in Patients with Linezolid-Induced Black Hairy Tongue: A Case Series

Linezolid-induced black hairy tongue is a self-limiting benign disease that is rare. Here, we report three patients who developed black hairy tongue after linezolid treatment. The severe dysbiosis of oral bacterial communities was observed in all these patients. Proteobacteria was the most prevalent phylum (over 90%) at the black tongue stage. Furthermore, the dramatic oral bacterial alteration took a long time to reverse after the BHT resolved.

Linezolid Exposure Is Associated with Cytopenias in Patients Treated for Multidrug-Resistant Tuberculosis

Although linezolid is effective for multidrug-resistant TB (MDR-TB) tuberculosis treatment, it is associated with cytopenias after 4 weeks of administration. Data on toxicities with long-term use of linezolid and drug pharmacodynamics in MDR-TB treatment are limited, and concerns about toxicity present barriers to wider implementation. This was a secondary analysis of a prospective cohort study of patients treated for MDR-TB in the country of Georgia from 2015 to 2017. Intensive blood sampling 4 to 6 weeks after treatment initiation with linezolid 600 mg daily was performed for pharmacokinetic (PK) analysis, including linezolid trough concentration (Cmin) and area under the curve from 0 to 24 hours (AUC0-24). Linezolid exposure was defined using literature-reported thresholds. Cytopenias were defined using an NIH adverse event (AE) scale. Logistic regression was used to evaluate the relationship between linezolid exposure and cytopenias. Among 76 patients receiving linezolid in their baseline treatment regimen and who had PK data available, cytopenia AEs occurred in 30 (39.5%) for an incidence rate of 46 per 100 person-years. The median duration of linezolid therapy was 526 days. No patients required dose reduction or interruption due to cytopenias. Median linezolid Cmin was 0.235 mg/L (interquartile range [IQR], 0.069 to 0.529), and median AUC0-24 was 89.6 mg·h/L (IQR, 69.2 to 116.2). Cytopenias were associated with linezolid PK parameters (Cmin > 2 mg/L and AUC0-24 > 160 mg·h/L). Cytopenias occurred frequently with long-term use of linezolid 600 mg/day and were associated with PK parameters but did not result in the need for treatment interruption in the management of a cohort of patients with MDR-TB.

Hijacking of the Enterobactin Pathway by a Synthetic Catechol Vector Designed for Oxazolidinone Antibiotic Delivery in Pseudomonas aeruginosa

Enterobactin (ENT) is a tris-catechol siderophore used to acquire iron by multiple bacterial species. These ENT-dependent iron uptake systems have often been considered as potential gates in the bacterial envelope through which one can shuttle antibiotics (Trojan horse strategy). In practice, siderophore analogues containing catechol moieties have shown promise as vectors to which antibiotics may be attached. Bis- and tris-catechol vectors (BCVs and TCVs, respectively) were shown using structural biology and molecular modeling to mimic ENT binding to the outer membrane transporter PfeA in Pseudomonas aeruginosa. TCV but not BCV appears to cross the outer membrane via PfeA when linked to an antibiotic (linezolid). TCV is therefore a promising vector for Trojan horse strategies against P. aeruginosa, confirming the ENT-dependent iron uptake system as a gate to transport antibiotics into P. aeruginosa cells.

Tissue Penetration of Antimicrobials in Intensive Care Unit Patients: A Systematic Review-Part II

In patients that are admitted to intensive care units (ICUs), the clinical outcome of severe infections depends on several factors, as well as the early administration of chemotherapies and comorbidities. Antimicrobials may be used in off-label regimens to maximize the probability of therapeutic concentrations within infected tissues and to prevent the selection of resistant clones. Interestingly, the literature clearly shows that the rate of tissue penetration is variable among antibacterial drugs, and the correlation between plasma and tissue concentrations may be inconstant. The present review harvests data about tissue penetration of antibacterial drugs in ICU patients, limiting the search to those drugs that mainly act as protein synthesis inhibitors and disrupting DNA structure and function. As expected, fluoroquinolones, macrolides, linezolid, and tigecycline have an excellent diffusion into epithelial lining fluid. That high penetration is fundamental for the therapy of ventilator and healthcare-associated pneumonia. Some drugs also display a high penetration rate within cerebrospinal fluid, while other agents diffuse into the skin and soft tissues. Further studies are needed to improve our knowledge about drug tissue penetration, especially in the presence of factors that may affect drug pharmacokinetics.

In vitro Susceptibility of Nontuberculous Mycobacteria to Tedizolid

Objective

Nontuberculous mycobacteria (NTM) can cause pulmonary and extrapulmonary diseases. Tedizolid (TZD) is a new oxazolidinone with in vitro activity against NTM such as Mycobacterium avium complex (MAC), Mycobacterium fortuitum, and Mycobacterium abscessus complex. The aim of this study was to evaluate the TZD susceptibility profiles of clinical isolates of NTM.

Methods

The microdilution method was used to identify the minimum inhibitory concentration (MIC) of TZD and linezolid (LZD) for 133 clinical NTM isolates. Broth microdilution chequerboard assays were used to investigate the synergistic effects of TZD and three antibiotics on two reference isolates and eleven clinical isolates of NTM.

Results

The TZD MIC₅₀ and MIC₉₀ for M. abscessus complex were 2 and 4 μg/mL, 16 and >32 μg/mL for MAC, respectively. TZD exhibited lower MICs than that of LZD for most NTM, which were positively correlated. Due to the high MIC values of TZD against MAC, it is necessary to conduct drug sensitivity tests before TZD administration. TZD-clarithromycin combination had synergistic response on M. abscessus complex in 3 of the 8 isolates, which lasted only 3-5 days. TZD-cefoxitin had synergistic effect against all five M. fortuitum isolates.

Conclusion

Our study demonstrates that TZD had greater in vitro potency than LZD, and synergy studies suggested that TZD may be an important component of multi-drug treatment regimen.

Revised Definitions of Tuberculosis Resistance and Treatment Outcomes, France, 2006-2019

Definitions of resistance in multidrug-resistant tuberculosis (MDR TB) and extensively drug-resistant tuberculosis (XDR TB) have been updated. Pre-XDR TB, defined as MDR TB with additional resistance to fluoroquinolones, and XDR TB, with additional resistance to bedaquiline or linezolid, are frequently associated with treatment failure and toxicity. We retrospectively determined the effects of pre-XDR/XDR TB resistance on outcomes and safety of MDR TB treatment in France. The study included 298 patients treated for MDR TB at 3 reference centers during 2006-2019. Of those, 205 (68.8%) cases were fluoroquinolone-susceptible MDR TB and 93 (31.2%) were pre-XDR/XDR TB. Compared with fluoroquinolone-susceptible MDR TB, pre-XDR/XDR TB was associated with more cavitary lung lesions and bilateral disease and required longer treatment. Overall, 202 patients (67.8%) had favorable treatment outcomes, with no significant difference between pre-XDR/XDR TB (67.7%) and fluoroquinolone-susceptible MDR TB (67.8%; p = 0.99). Pre-XDR/XDR TB was not associated with higher risk for serious adverse events.

A Structurally Characterized Staphylococcus aureus Evolutionary Escape Route from Treatment with the Antibiotic Linezolid

Methicillin-resistant Staphylococcus aureus (MRSA) is a bacterial pathogen that presents great health concerns. Treatment requires the use of last-line antibiotics, such as members of the oxazolidinone family, of which linezolid is the first member to see regular use in the clinic. Here, we report a short time scale selection experiment in which strains of MRSA were subjected to linezolid treatment. Clonal isolates which had evolved a linezolid-resistant phenotype were characterized by whole-genome sequencing. Linezolid-resistant mutants were identified which had accumulated mutations in the ribosomal protein uL3. Multiple clones which had two mutations in uL3 exhibited resistance to linezolid, 2-fold higher than the clinical breakpoint. Ribosomes from this strain were isolated and subjected to single-particle cryo-electron microscopic analysis and compared to the ribosomes from the parent strain. We found that the mutations in uL3 lead to a rearrangement of a loop that makes contact with Helix 90, propagating a structural change over 15 Å away. This distal change swings nucleotide U2504 into the binding site of the antibiotic, causing linezolid resistance. IMPORTANCE Antibiotic resistance poses a critical problem to human health and decreases the utility of these lifesaving drugs. Of particular concern is the "superbug" methicillin-resistant Staphylococcus aureus (MRSA), for which treatment of infection requires the use of last-line antibiotics, including linezolid. In this paper, we characterize the atomic rearrangements which the ribosome, the target of linezolid, undergoes during its evolutionary journey toward becoming drug resistant. Using cryo-electron microscopy, we describe a particular molecular mechanism which MRSA uses to become resistant to linezolid.

Linezolid in the treatment of severe intraabdominal infection: A STROBE-compliant retrospective study

Safety concerns over bone marrow suppression and thrombocytopenia may inhibit the use of linezolid to treat intraabdominal infection (IAI). To evaluate the effectiveness, safety, and prognosis of linezolid in the treatment of severe IAI (SIAI). Patients were divided into a linezolid group and nonlinezolid group according to whether linezolid was prescribed. Subgroup analysis (thrombocytopenia treated with linezolid group (I), and thrombocytopenia treated with nonlinezolid group (II) also was performed. We evaluated the effectiveness of linezolid by analyzing the changes in white blood cells (WBC) and procalcitonin, evaluated safety by analyzing the changes in platelet counts, and evaluated patient outcomes by analyzing the length of hospital stay, the length of ICU stay, and the rates of clinical improvement. Sixty-six adult SIAI patients were treated with anti-gram-positive (G+) bacteria drugs for more than 7 days from January 1, 2014, to December 31, 2020. The length of hospital stay, the length of ICU stay, and the rates of clinical improvement were not significantly different between the linezolid group and nonlinezolid group. On the 15th day after anti-G + bacteria treatment, the WBC of the linezolid group was significantly lower than in the nonlinezolid group (9.00 ± 4.30 vs 13.1 ± 6.19, P < .05). The time for a statistical difference in the decrease of procalcitonin in the linezolid group was earlier than in the nonlinezolid group (day 6 vs day 7, P < .05). There was no statistically significant difference in the changes of platelet counts in the subgroup I (P > .05), but compared with the baseline data (day 0), the time for the statistical difference in the increase of platelets in thrombocytopenia treated with linezolid group was earlier (day 5 vs day 6, P < .05). There was no statistical difference in the changes of platelets in subgroup II (P > .05). In the treatment of severe intraabdominal infection in a single-center, retrospective study, linezolid was not inferior to other antibiotics in patient clinical outcomes or seral WBC and procalcitonin values. Linezolid also induced no evident bone marrow suppression or thrombocytopenia. Linezolid is a good choice for treatment of SIAI.

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.

Linezolid-Induced Pure Red Cell Aplasia: A Case Report

Linezolid (LZD) has been widely used for treating the infections of multidrug-resistant gram-positive organisms. As we know, anemias induced by Linezolid (LZD) are common. However, LZD-induced pure red cell aplasia (PRCA) is very rare. In this paper, we report on a 68-year-old woman with intravascular stent infection who developed PRCA after treatment with LZD. The patient presented to our hospital with a 6-month history of fever after stent implantation for aneurysms in both lower limbs. Bone culture grew methicillin-resistant Staphylococcus hemolyticus (MRSH). She received LZD after developing adverse reactions to initial antibiotics. Although her infective symptoms were improved by LZD, progressive thrombocytopenia was observed 23 days after LZD therapy. Her platelets declined to 66*10⁹/L and hemoglobin level was 10.1 g/dL. Thrombocytopenia recovered 12 days after cessation of LZD. LZD was administered again due to recovered fever. 57 days after LZD administration, her hemoglobin level was 4.1 g/dL and reticulocytes were 0.2%. Bone marrow smear revealed active granulocyte proliferation and markedly decreased erythropoiesis with vacuolar degeneration. 12 days after cessation of LZD, her hemoglobin and reticulocyte levels rose to 9.6 g/dL and 5.1%, respectively. LZD was used for the third time as fever and inflammatory markers progressively increased, but Hb was reduced to 6.7g/dL 15 days after LZD therapy. 12 days after cessation of LZD, the hemoglobin level rose to 11.9 g/dL. In summary, we suggest complete blood count and reticulocyte count should be monitored to detect bone marrow suppression during long-term LZD therapy, especially in patients aged over 58 and/or with pre-existing anemia, chronic infections, and renal insufficiency.

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

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

Enumeration, Antimicrobial Resistance, and Virulence Genes Screening of Enterococcus spp. Isolated from Retail Chicken Carcasses in the United Arab Emirates

Enterococci have recently emerged as nosocomial pathogens worldwide. Their ubiquitous nature determines their frequent finding in foods as contaminants. In this study, we aimed to determine the counts, species diversity, antimicrobial resistance profile, and to screen for a set of virulence genes among enterococci. Enterococcus were identified from 75.7% (125/165) of chilled chicken carcasses, belonging to seven companies, sampled from retail markets in Abu Dhabi Emirate, United Arab Emirates (U.A.E.). Overall, the samples, with a mean Enterococcus count of 2.58 log₁₀ colony-forming unit (CFU)/g with a standard deviation of ±1.17 log₁₀ CFU/g. Among the characterized Enterococcus isolates (n = 90), Enterococcus faecalis was the predominant species (51.1%), followed by Enterococcus faecium (37.8%). Using Vitek2 automated antimicrobial sensitivity panel, we found none of the E. faecalis nor E. faecium to be resistant to ampicillin, teicoplanin, vancomycin, or tigecycline. A third of the E. faecalis (28.3%) and E. faecium (35.3%) were resistant to high-level gentamicin. Over half of E. faecalis (54.3%) were resistant to ciprofloxacin, and the same was in about a third of E. faecium isolates (29.4%). Linezolid resistance was identified in 10 E. faecalis and 7 E. faecium isolates belonging to samples from three companies. All of the linezolid-resistant isolates harbored oxazolidinone resistance optrA gene. Virulence-associated genes (asa1 and gelE) were significantly (p < 0.05) more detected among E. faecalis compared to E. faecium isolates recovered in this study. Over half of the E. faecalis (25/46) and E. faecium (20/34) isolates were identified as multidrug-resistant. This study provides further insight into virulence genes and their association with the dissemination of multidrug-resistant E. faecalis and E. faecium in supermarket chicken meat in the U.A.E. This is probably the first description of the optrA gene in enterococci from supermarket chicken meat in the U.A.E. and from Arab countries. This study adds to the regional and global understanding of antimicrobial resistance spread in foods of animal origin.

Detection of the optrA Gene Among Polyclonal Linezolid-Susceptible Isolates of Enterococcus faecalis Recovered from Community Patients

Dispersion of transferable oxazolidinone resistance genes among enterococci poses a serious problem to human health. Prompt detection of bacteria carrying these genes is crucial to avoid their spread to multidrug-resistant bacteria. The aim of the study was to describe the presence of optrA-positive isolates among enterococci in a Spanish hospital, and to determine their genetic context and location through whole genome sequencing. All enterococci recovered in a Spanish hospital (Hospital El Bierzo; HEB) from February to December 2018 (n = 443), with minimal inhibitory concentrations (MICs) to linezolid (LZD) ≥4 mg/L, were tested by polymerase chain reaction for the presence of cfr, optrA, and poxtA transferable genes. Only four Enterococcus faecalis isolates (0.9%) had LZD MICs ≥4 mg/L and none of them was positive for cfr or poxtA genes. However, the optrA gene was detected in three isolates collected from urine samples of community patients, whose genomes were sequenced and subjected to bioinformatics analysis. These isolates belonged to different clones: ST7, ST480, and ST585. In these three isolates, the optrA gene was located on plasmids, associated with IS1216 in different arrays. In one isolate, the optrA plasmid coexists with a second plasmid, which carried multiple resistance genes for different classes of antibiotics. Detection of optrA-positive E. faecalis isolates in the community is a matter of concern. The spread of these bacteria into hospital settings, particularly in those, such as the HEB, where vancomycin-resistant enterococci are endemic, should be avoided, to preserve the efficacy of the last-resort oxazolidinones.

Case Report: Disseminated Nocardiosis Caused by Nocardia vulneris in a Patient With Macroglobulinemia

This report describes a case of disseminated nocardiosis, caused by Nocardia vulneris, in a 61-year-old man with macroglobulinemia and presenting with repeated fever, cough, shortness of breath, and muscle pain. The isolated Nocardia strain was resistant to ciprofloxacin, but susceptible to amikacin, gentamicin, tobramycin, linezolid, trimethoprim-sulfamethoxazole, amoxicillin/clavulanic, moxifloxacin, ceftriaxone, cefotaxim, and imipenem. The patient was started on combined meropenem and doxycycline treatment, followed by trimethoprim-sulfamethoxazole, which was subsequently switched to a combination treatment of linezolid, amikacin, and trimethoprim-sulfamethoxazole. The patient recovered, and his condition remained stable. Although infection by Nocardia vulneris is rare, and it is easy to miss detection in clinical practice, clinicians should be aware of the possibility of this infection. In addition, the MIC value of the drug sensitivity test should be ascertained when there is a wide choice of medicines. The current case was treated successfully with linezolid, amikacin, and trimethoprim-sulfamethoxazole. In cases of disseminated nocardiosis, the patient should be treated with antimicrobial therapy for at least 12 months. Furthermore, bacteriological examination and antimicrobial susceptibility testing should be performed regularly.

Linezolid for resistant Gram-positive bacterial infections in children under 12 years: A meta-analysis

Both linezolid and vancomycin have good efficacy in the treatment of resistant Gram-positive bacterial infections. This systematic review and meta-analysis aimed to compare the efficacy and safety of linezolid vs vancomycin for the treatment of resistant Gram-positive bacterial infections in children under 12 years. Five randomly controlled trials involving 638 children that were treated with linezolid and vancomycin for resistant Gram-positive bacterial infections were searched from medical databases. Meta-analysis showed that linezolid and vancomycin had equivalent efficacies in clinical cure rates in the intent-to-treat population (95% confidence interval [CI] 0.88, 2.09) and microbiologically evaluable patients (95% CI: 0.46, 2.47). Linezolid and vancomycin also had equivalent pathogen eradication rates for Staphylococcus aureus (95% CI: 0.31, 4.81), methicillin-resistant S. aureus (95% CI: 0.36, 5.34), Enterococcus faecalis (95% CI: 0.32, 8.76), and coagulase-negative Staphylococci (95% CI: 0.43, 4.01). Vancomycin resulted in a higher incidence of alanine aminotransferase increase (95% CI: 0.37, 0.97), red man syndrome (95% CI: 0.01, 0.28), and rash (95% CI: 0.11, 0.73) than linezolid. Clinically, linezolid had a superior safety to vancomycin for resistant Gram-positive infections. Linezolid might be prescribed for the treatment of resistant Gram-positive bacterial infections in children under 12 years.

Linezolid decreases Staphylococcus aureus biofilm formation by affecting the IcaA and IcaB proteins

Background

The ica gene of Staphylococcus aureus (S. aureus) plays a vital role in its growth and biofilm formation. Among them, IcaA and IcaB are critical proteins for synthesizing extracellular polysaccharides and biofilms in S. aureus. To investigate whether the formation of S. aureus biofilms can be inhibited through the IcaA and IcaB proteins by the presence of linezolid.

Methods

The icaA and icaB genes of S. aureus ATCC 25923 were silenced by homologous recombination. The critical roles of icaA and icaB in S. aureus were analysed by observing the growth curve and biofilm formation after linezolid treatment. Then, the effect of linezolid on the morphology of S. aureus was observed by scanning electron microscopy. Finally, the potential binding ability of linezolid to Ica proteins was predicted by molecular docking.

Results

The icaA- and icaB-silenced strains were successfully constructed, and the sensitivity of S. aureus to linezolid was decreased after icaA and icaB silencing. Scanning electron microscopy showed that linezolid caused invagination of the S. aureus surface and reduced the production of biofilms. Molecular docking results showed that linezolid could bind to IcaA and IcaB proteins.

Conclusion

IcaA and IcaB are potential targets of linezolid in inhibiting the biofilm formation of S. aureus (ATCC 25923).