Oxazolidinone antibiotics impair ex vivo megakaryocyte differentiation from hematopoietic progenitor cells and their maturation into platelets.

Oxazolidinones (linezolid and tedizolid) adverse reactions include thrombocytopenia, the mechanism of which is still largely unknown. In cultured cells, oxazolidinones impair mitochondrial protein synthesis and oxidative metabolism. As mitochondrial activity is essential for megakaryocyte differentiation and maturation into platelets, we examined whether oxazolidinones impair these processes ex vivo and alter, in parallel, the activity of mitochondrial cytochrome c-oxidase (CYTOX; enzyme partly encoded by the mitochondrial genome) and cell morphology. Human CD34+ cells were isolated, incubated with cytokines (up to 14 days) and clinically relevant oxazolidinone concentrations or in control conditions, and used for (i) clonogenic assays [counting of megakaryocyte (CFU-Mk), granulocyte-monocyte (CFU-GM), burst-forming unit-erythroid (BFU-E) colonies]; (ii) the measure of the expression of megakaryocyte surface antigens (CD34 to CD41 and CD42); (iii) counting of proplatelets; (iv) the measurement of CYTOX activity; and (v) cell morphology (optic and electron microscopy). Oxazolidinones caused a significant decrease in BFU-E but not CFU-Mk or CFU-GM colonies. Yet, the megakaryocytic lineage was markedly affected, with a decreased differentiation of CD34+ into CD41+/CD42+ cells, an abolition of proplatelet formation and striking decrease in the numbers of large polylobulated nucleus megakaryocytes, with a complete loss of intracellular demarcation membrane system, disappearance of mitochondria, and suppression of CYTOX activity. These alterations were more marked in cells incubated with tedizolid than linezolid. These data suggest that oxazolidinones may induce thrombocytopenia by impairing megakaryocytic differentiation through mitochondrial dysfunction. Pharmacological interventions to prevent this toxicity might therefore be difficult as mitochondrial toxicity is most probably inherently linked to their antibacterial activity.

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.

Adverse Drug Reactions to Antiretroviral Therapy: Frequency, Type, and Risk Factors in Children in Mali.

OBJECTIVE: The aim of our study was to evaluate the frequency, type, and risk factors associated with adverse drug reactions (ADRs) in HIV-positive children with adherence to antiretroviral therapy (ART) at the Unit of Care and Accompaniment for People Living With HIV (USAC) of Bamako. METHODS: A cross-sectional study was conducted at USAC of Bamako from May 1, 2014, to July 31, 2015. We included children aged 1 to 14 years with at least 6 months of ARV treatment initiated at USAC, with or without ADRs. Data collection was based on information collected from parents and clinical/biological assessments. RESULTS: Median age of participants was 36 months and female sex was predominant (54.8%). Poor adherence during the study was observed in 15% of cases. Of patients in the study, 52% had a CD4 count less than 350 cells/mm3 at the time of adverse events. In bivariate analysis, we found that participants with adherence to ART tended to be younger than those with non-adherence to ART (36 vs 72 months, p = 0.093). In multivariable analysis, prophylactic treatment was the only factor marginally associated with ART adherence in HIV patients (p = 0.09). No other adverse biological effects or clinical conditions were associated with ART adherence in this study. CONCLUSIONS: In this study we found that ADRs were frequent in HIV-positive patients but less frequent in ART-adherent HIV-positive children. Therefore, it is essential to regularly monitor children receiving ARVs to detect and treat the complications associated with these therapies according to ART adherence.

Editorial for the Special Issue "A Themed Issue in Honor of Professor Hartmut Derendorf-Outstanding Contributions in the Fields of Quantitative Clinical Pharmacology".

Pharmacokinetics (PK) is the discipline investigating the absorption, distribution, metabolization and elimination of a drug in the body [...].

Binding of temocillin to plasma proteins in vitro and in vivo: the importance of plasma protein levels in different populations and of co-medications.

BACKGROUND: Temocillin plasma protein binding (PPB) in healthy individuals is reported to be ∼85% but had not been studied in patients. OBJECTIVES: To obtain normative data on temocillin PPB in patients in relation to infection and impact of co-medications widely used in ICU. METHODS: Plasma was obtained from healthy individuals (Group #1), non-ICU patients with UTI (Group #2), ICU patients with suspected/confirmed ventriculitis (Group #3) or with sepsis/septic shock (Group #4). Total and unbound temocillin concentrations were measured in spiked samples from temocillin-naive donors (in vitro) or in plasma from temocillin-treated subjects (in vivo). The impact of diluting plasma, using pharmaceutical albumin, or adding drugs potentially competing for PPB was tested in spiked samples. Data were analysed using a modified Hill-Langmuir equation taking ligand depletion into account. RESULTS: Temocillin PPB was saturable in all groups, both in vitro and in vivo. Maximal binding capacity (Bmax) was 1.2-2-fold lower in patients. At 20 and 200 mg/L (total concentrations), the unbound fraction reached 12%-29%, 23%-42% and 32%-52% in Groups #2, #3, #4. The unbound fraction was inversely correlated with albumin and C-reactive protein concentrations. Binding to albumin was 2-3-fold lower than in plasma and non-saturable. Drugs with high PPB but active at lower molar concentrations than temocillin caused minimal displacement, while fluconazole (low PPB but similar plasma concentrations to temocillin) increased up to 2-fold its unbound fraction. CONCLUSIONS: Temocillin PPB is saturable, 2-4-fold lowered in infected patients in relation to disease severity (ICU admission, hypoalbuminaemia, inflammation) and only partially reproducible with albumin. Competition with other drugs must be considered for therapeutic concentrations to be meaningful.

Population Pharmacokinetics of Temocillin Administered by Continuous Infusion in Patients with Septic Shock Associated with Intra-Abdominal Infection and Ascitic Fluid Effusion.

Temocillin is active against Gram-negative bacteria, including many extended-spectrum ß-lactamase (ESBL)-producing Enterobacterales. We studied its pharmacokinetics in plasma and ascitic fluid after intravenous administration of a loading dose of 2 g over 30 min, followed by continuous infusion of 6 g/24 h, to 19 critically-ill patients with septic shock associated with complicated intra-abdominal infection. We established a pharmacokinetic model describing unbound temocillin concentrations in plasma and ascitic fluid and performed Monte-Carlo simulations to evaluate the probability of target attainment (PTA) of unbound concentrations (100% fT > MIC, i.e., unbound concentrations remaining above the MIC during 100% of the time) for the applied and hypothetical dosing regimens. The temocillin AUC in ascitic fluid was 46% of the plasma AUC. Plasma unbound concentrations were best described by a two-compartment model, and an additional compartment was added to describe unbound concentration in ascitic fluid, with renal clearance as a covariate. Dosing simulations showed that 90% PTA was achieved in the plasma with the current dosing regimen for MIC ≤ 16 mg/L (EUCAST susceptibility breakpoint) but not in the ascitic fluid if renal clearance was ≥40 mL/min. Hypothetical dosing with a higher (a) loading dose or (b) infused dose allowed to reach target concentrations in ascitic fluid (a) more rapidly or (b) sustainably, but these simulations need to be evaluated in the clinics for safety and efficacy.

Current and future options for treating complicated skin and soft tissue infections: focus on fluoroquinolones and long-acting lipoglycopeptide antibiotics.

Bacterial skin and soft tissue infections are among the most common bacterial infections and constitute a major burden for patients and healthcare systems. Care is complicated by the variety of potential pathogens, some with resistance to previously effective antimicrobial agents, the wide spectrum of clinical presentations and the risk of progression to life-threatening forms. More-efficient care pathways are needed that can reduce hospital admissions and length of stay, while maintaining a high quality of care and adhering to antimicrobial stewardship principles. Several agents approved recently for treating acute bacterial skin and skin structure infections have characteristics that meet these requirements. We address the clinical and pharmacological characteristics of the fourth-generation fluoroquinolone delafloxacin, and the long-acting lipoglycopeptide agents dalbavancin and oritavancin.

In Vitro Models for the Study of the Intracellular Activity of Antibiotics.

Intracellular bacteria are poorly responsive to antibiotic treatment. Pharmacological studies are thus needed to determine the antibiotics which are the most potent or effective against intracellular bacteria as well as to explore the reasons for poor bacterial responsiveness. An in vitro pharmacodynamic model is described, consisting of (1) phagocytosis of preopsonized bacteria by eukaryotic cells, (2) elimination of noninternalized bacteria with gentamicin, (3) incubation of infected cells with antibiotics, and (4) determination of surviving bacteria by viable cell counting and normalization of the counts based on sample protein content. The use of strains expressing fluorescent proteins under the control of an inducible promoter allows to follow intracellular bacterial division at the individual level and therefore to monitor bacterial persisters that do not multiply anymore.

Uropathogenic Escherichia coli Shows Antibiotic Tolerance and Growth Heterogeneity in an In Vitro Model of Intracellular Infection.

Uropathogenic Escherichia coli (UPEC), the major causative agent of urinary tract infections, can invade different types of host cells. To compare the pharmacodynamic properties of antibiotics against intra- and extracellular UPEC, an in vitro model of intracellular infection was established in J774 mouse macrophages infected by the UPEC strain CFT073. We tested antibiotics commonly prescribed against urinary tract infections (gentamicin, ampicillin, nitrofurantoin, trimethoprim, sulfamethoxazole, and ciprofloxacin) and the investigational fluoroquinolone finafloxacin. The metabolic activity of individual bacteria was assessed by expressing the fluorescent reporter protein TIMERbac within CFT073. Concentration-response experiments revealed that all tested antibiotics were much less effective against intracellular bacteria than extracellular ones. Most antibiotics, except fluoroquinolones, were unable to reach a bactericidal effect intracellularly at clinically achievable concentrations. Ciprofloxacin and finafloxacin killed 99.9% of extracellular bacteria at concentrations around the MIC, while for intracellular bacteria, concentrations more than 100× over the MIC were required to achieve a bactericidal effect. Time-kill curves showed that finafloxacin was more rapidly bactericidal in acidic medium than at neutral pH, while the reverse observation was made for ciprofloxacin. Intracellularly, kill curves showed biphasic kinetics for both fluoroquinolones, suggesting the presence of drug-tolerant subpopulations. Flow cytometry analysis of TIMERbac fluorescence revealed a marked heterogeneity in intracellular growth of individual bacteria, suggesting that the presence of subpopulations reaching a state of metabolic dormancy was the main reason for increased antibiotic tolerance of intracellular UPEC.

Clinical Use and Adverse Drug Reactions of Linezolid: A Retrospective Study in Four Belgian Hospital Centers.

In Belgium, linezolid is indicated for pneumonia and skin and soft tissue infections, but is more broadly used, due to its oral bioavailability and activity against multiresistant organisms. This could increase the risk of adverse drug reactions (ADR), notably hematological disorders (anemia, thrombocytopenia), neuropathy, or lactic acidosis. We analyzed linezolid clinical use in relationship with occurrence of ADR in Belgian hospitals and highlighted risk factors associated with the development of thrombocytopenia. A retrospective analysis of electronic medical records and laboratory tests of adult patients treated with linezolid in four Belgian hospitals in 2016 allowed the collection of ADR for 248 linezolid treatments. Only 19.7% of indications were in-label. ADR included 43 thrombocytopenia, 17 anemia, 4 neuropathies, and 4 increases in lactatemia. In a multi-variate analysis, risk factors of thrombocytopenia were a treatment duration > 10 days, a glomerular filtration rate < 60 mL/min, and a Charlson index ≥ 4. Off-label use of linezolid is frequent in Belgium, and ADR more frequent than reported in the summary of product characteristics, but not statistically associated with any indication. This high prevalence of ADR could be related to a high proportion of patients presenting risk factors in our population, highlighting the importance of detecting them prospectively.

Activity of Moxifloxacin Against Biofilms Formed by Clinical Isolates of Staphylococcus aureus Differing by Their Resistant or Persister Character to Fluoroquinolones.

Staphylococcus aureus biofilms are poorly responsive to antibiotics. Underlying reasons include a matrix effect preventing drug access to embedded bacteria, or the presence of dormant bacteria with reduced growth rate. Using 18 clinical isolates previously characterized for their moxifloxacin-resistant and moxifloxacin-persister character in stationary-phase culture, we studied their biofilm production and matrix composition and the anti-biofilm activity of moxifloxacin. Biofilms were grown in microtiter plates and their abundance quantified by crystal violet staining and colony counting; their content in polysaccharides, extracellular DNA and proteins was measured. Moxifloxacin activity was assessed after 24 h of incubation with a broad range of concentrations to establish full concentration-response curves. All clinical isolates produced more biofilm biomass than the reference strain ATCC 25923, the difference being more important for those with high relative persister fractions to moxifloxacin, most of which being also resistant. High biofilm producers expressed icaA to higher levels, enriching the matrix in polysaccharides. Moxifloxacin was less potent against biofilms from clinical isolates than from ATCC 25923, especially against moxifloxacin-resistant isolates with high persister fractions, which was ascribed to a lower concentration of moxifloxacin in these biofilms. Time-kill curves in biofilms revealed the presence of a moxifloxacin-tolerant subpopulation, with low multiplication capacity, whatever the persister character of the isolate. Thus, moxifloxacin activity depends on its local concentration in biofilm, which is reduced in most isolates with high-relative persister fractions due to matrix effects, and insufficient to kill resistant isolates due to their high MIC.

The Persister Character of Clinical Isolates of Staphylococcus aureus Contributes to Faster Evolution to Resistance and Higher Survival in THP-1 Monocytes: A Study With Moxifloxacin.

Staphylococcus aureus may cause relapsing infections. We previously showed that S. aureus SH1000 surviving intracellularly to bactericidal antibiotics are persisters. Here, we used 54 non-duplicate clinical isolates to assess links between persistence, resistance evolution, and intracellular survival, using moxifloxacin throughout as test bactericidal antibiotic. The relative persister fraction (RPF: percentage of inoculum surviving to 100× MIC moxifloxacin in stationary phase culture for each isolate relative to ATCC 25923) was determined to categorize isolates with low (≤10) or high (>10) RPF. Evolution to resistance (moxifloxacin MIC ≥ 0.5 mg/L) was triggered by serial passages at 0.5× MIC (with daily concentration readjustments). Intracellular moxifloxacin maximal efficacy (Emax) was determined by 24 h concentration-response experiments [pharmacodynamic model (Hill-Langmuir)] with infected THP-1 monocytes exposed to moxifloxacin (0.01 to 100× MIC) after phagocytosis. Division of intracellular survivors was followed by green fluorescence protein dilution (FACS). Most (30/36) moxifloxacin-susceptible isolates showed low RPF but all moxifloxacin-resistant (n = 18) isolates harbored high RPF. Evolution to resistance of susceptible isolates was faster for those with high vs. low RPF (with SOS response and topoisomerase-encoding genes overexpression). Intracellularly, moxifloxacin Emax was decreased (less negative) for isolates with high vs. low RPF, independently from resistance. Moxifloxacin intracellular survivors were non-dividing. The data demonstrate and quantitate persisters in clinical isolates of S. aureus, and show that this phenotype accelerates resistance evolution and is associated with intracellular survival in spite of high antibiotic concentrations. Isolates with high RPF may represent a possible cause of treatment failure not directly related to resistance in patients receiving active antibiotics.

Artemisia Spp. Derivatives for COVID-19 Treatment: Anecdotal Use, Political Hype, Treatment Potential, Challenges, and Road Map to Randomized Clinical Trials.

The world is currently facing a novel COVID-19 pandemic caused by SARS-CoV-2 that, as of July 12, 2020, has caused a reported 12,322,395 cases and 556,335 deaths. To date, only two treatments, remdesivir and dexamethasone, have demonstrated clinical efficacy through randomized controlled trials (RCTs) in seriously ill patients. The search for new or repurposed drugs for treatment of COVID-19 continues. We have witnessed anecdotal use of herbal medicines, including Artemisia spp. extracts, in low-income countries, and exaggerated claims of their efficacies that are not evidence based, with subsequent political controversy. These events highlight the urgent need for further research on herbal compounds to evaluate efficacy through RCTs, and, when efficacious compounds are identified, to establish the active ingredients, develop formulations and dosing, and define pharmacokinetics, toxicology, and safety to enable drug development. Derivatives from the herb Artemisia annua have been used as traditional medicine over centuries for the treatment of fevers, malaria, and respiratory tract infections. We review the bioactive compounds, pharmacological and immunological effects, and traditional uses for Artemisia spp. derivatives, and discuss the challenges and controversies surrounding current efforts and the scientific road map to advance them to prevent or treat COVID-19.

Comparative in vitro antimicrobial potency, stability, colouration and dissolution time of generics versus innovator of meropenem in Europe.

Meropenem generics are often imposed on prescribers, however scarce information is available on key properties such as antimicrobial potency, stability and colouration in solution, and dissolution time. This study aimed to generate comparative information for products available in Europe. The originator (ASTRA) and four generics (HOSPIRA, SANDOZ, FRESENIUS and AUROVIT) were compared for: (i) MICs against Pseudomonas aeruginosa clinical isolates (range, 0.125-191 mg/L); (ii) colouration (visual and photometry) and stability of concentrated solutions for prolonged or continuous infusion and maintained at 25-37 °C for up to 8 h (acceptable limit, ≥90% of original concentration); and (iii) dissolution time of concentrated solutions (50 mg/mL [for bolus administration]: turbidimetry and nursing personnel assessment). No significant difference was observed for MICs (except 2/80 isolates). For concentrated solutions storage: (i) SANDOZ produced about two times more yellow-coloured degradation products than the other preparations; (ii) meropenem loss was time-, concentration- and temperature-dependent; (iii) FRESENIUS was the least stable (limit for 1 g/48 mL, ~8 h at 25 °C and 4.5 h at 37 °C); (iv) at 2 g/48 mL, the storage time limit was 5-6 h at 25 °C and ~3 h at 37 °C for all preparations. Complete dissolution (turbidimetry) required 240 s for generics (120 s for ASTRA), and nurses reported longer but highly variable times for generics. Substantial differences between innovator and generics have been identified that could impact on their clinical use and/or make multicentric studies difficult to interpret, requiring suitability studies in the environments of their intended use.

Cellular pharmacokinetics and intracellular activity of the bacterial fatty acid synthesis inhibitor, afabicin desphosphono against different resistance phenotypes of Staphylococcus aureus in models of cultured phagocytic cells.

Antibiotics with new modes of action that are active against intracellular forms of Staphylococcus aureus are sorely needed to fight recalcitrant infections caused by this bacterium. Afabicin desphosphono (Debio 1452, the active form of afabicin [Debio 1450]) is an inhibitor of FabI enoyl-Acyl carrier protein reductase and has specific and extremely potent activity against Staphylococci, including strains resistant to current antistaphylococcal agents. Using mouse J774 macrophages and human THP-1 monocytes, we showed that afabicin desphosphono: (i) accumulates rapidly in cells, reaching stable cellular-to-extracellular concentration ratios of about 30; (ii) is recovered entirely and free in the cell-soluble fraction (no evidence of stable association with proteins or other macromolecules). Afabicin desphosphono caused a maximum cfu decrease of about 2.5 log10 after incubation in broth for 30 h, including against strains resistant to vancomycin, daptomycin, and/or linezolid. Using a pharmacodynamic model of infected THP-1 monocytes (30 h of incubation post-phagocytosis), we showed that afabicin desphosphono is bacteriostatic (maximum cfu decrease: 0.56 to 0.73 log10) towards all strains tested, a behaviour shared with the comparators (vancomycin, daptomycin, and linezolid) when tested against susceptible strains. We conclude that afabicin desphosphono has a similar potential as vancomycin, daptomycin or linezolid to control the intracellular growth and survival of phagocytized S. aureus and remains fully active against strains resistant to these comparators.

Antibiotic Resistance, Biofilm Formation, and Intracellular Survival As Possible Determinants of Persistent or Recurrent Infections by Staphylococcus aureus in a Vietnamese Tertiary Hospital: Focus on Bacterial Response to Moxifloxacin.

Resistance is notoriously high in Asia but may not entirely explain therapeutic failures. Specific modes of bacterial life, such as biofilm or intracellular survival, may also contribute to the persistent and/or recurrent character of infections. Most Staphylococcus aureus isolates form biofilm and many survive and even thrive intracellularly. We collected 36 nonduplicate S. aureus isolates (including 18 methicillin-resistant S. aureus) from patients with clinical evidence of persistent or recurrent infections in a large tertiary Vietnamese hospital. We examined their antibiotic resistance profile (minimal inhibitory concentration determination) and clonal relatedness (spa and agr typing, pulsed field gel electrophoresis profiles). We then assessed the activity of moxifloxacin in both biofilms and infected phagocytes (moxifloxacin previously proved to be one of the most active antibiotics against reference strains in these models). spa-types t189 and t437 and agr group I were the most frequent. Among the 36 isolates, 30 were multidrug resistant but 30 were recovered from patients having received an active drug. All tested isolates produced biofilm and survived inside phagocytes. At its human Cmax, moxifloxacin was inactive on biofilms made by moxifloxacin-susceptible as well as moxifloxacin-resistant isolates. It caused only a modest intracellular colony-forming unit decrease against moxifloxacin-susceptible isolates and was inactive against those resistant to moxifloxacin. While our data confirm for this collection the high resistance levels and prevalence of endemic spa- or agr- types in Asia, they show that tolerance in both biofilm and phagocytes are correlated and markedly limit moxifloxacin activity, which goes in line with the suggested role of these modes of life in persistence or recurrence of infections.

Antiretroviral-induced adverse drug reactions in HIV-infected patients in Mali: a resource-limited setting experience.

BACKGROUND: There are few reports in the literature from sub-Saharan Africa (SSA) regarding antiretroviral-induced adverse drug reactions (ADRs). Antiretroviral therapy (ART) is now widely available in SSA, and ADRs during HIV infection are also frequent. In this study, we reported the frequency and risk factors of ART-induced ADRs in a Malian population. METHODS: This prospective cohort study was performed in the HIV Care and Counseling Centre (CESAC) of Mali from 2011 to 2012. Adult patients infected with HIV and who had recently started ART were included and followed-up clinically Were included in this study, adult patients living with HIV and had recently started ART who were followed up for at least 6 months to determine the incidence of ADRs using Naranjo's classification scale. RESULTS: During this study, 357 (42.3%) patients presented ADRs (40.1% of our patients (n=338) experienced at least one ADR, and 2.2% (n=19) experienced at least two ADRs). The prevalence of ADRs by organ system was: 45.9% neurological (n=164); 29.4% metabolic (blood chemistry) (n=105); 15.4% hematological (n=55). High probable rate of ADR was observed as indicated by the Naranjo score in 83.7% of the cases. Zidovudine (AZT) and stavudine (d4T) use was identified as a risk factor for either anaemia or peripheral neuropathy whereas nevirapine (NVP) and female gender were risk factors for skin reactions. Patients with advance disease had the highest rate of ADRs compared to the others. CONCLUSIONS: Based on the Naranjo probability scale, our data show that ADRs such as peripheral neuropathy and anemia are very frequent. These ADR was linked to AZT and D4T. Our findings highlight the need for active monitoring, continuous pharmacovigilance of ART and change of some ART drug in this population.

Determination of optimal loading and maintenance doses for continuous infusion of vancomycin in critically ill patients: Population pharmacokinetic modelling and simulations for improved dosing schemes.

OBJECTIVES: Despite extensive clinical use, limited data are available on optimal loading and maintenance doses of vancomycin in critically ill patients. This study aimed to develop a rational approach for optimised dosage of vancomycin given in a continuous infusion in critically ill patients. METHODS: Vancomycin pharmacokinetic (PK) data (total serum concentrations) were obtained from 55 intensive care unit (ICU) patients (Bach Mai Hospital, Hanoi, Vietnam) receiving a 20 mg/kg loading dose followed by continuous infusion stratified by creatinine clearance (CLCr). Population PK modelling and Monte Carlo simulations were performed using a nonlinear mixed-effects modelling (NONMEM) program for a target of 20-30 mg/L to optimise efficacy and minimise nephrotoxicity. RESULTS: A two-compartment model with first-order elimination best fitted the PK data with central and peripheral volumes of distribution of 1.01 and 2.39 L/kg, respectively (allometric scaling to a 70 kg standard subject). The population total clearance of 3.63 L/h was only explained by renal function in the covariate and final model. The simulations showed that a 25-mg/kg loading dose infused over 90 minutes was optimal to reach the target range. The optimal maintenance dose for low renal function (CLCr < 45 mL/min) was 1000-1500 mg/day. For augmented renal clearance (CLCr > 130 mL/min) the dose should be up to 3500 mg/day or even 4500 mg/day to achieve adequate exposure. These simulated maintenance doses were larger than previously proposed for non-ICU patients. CONCLUSION: Large loading and maintenance doses of vancomycin are generally needed in critically ill patients. Because of high interindividual variability in vancomycin PK, drug monitoring may still be necessary.

Prolonged inhibition and incomplete recovery of mitochondrial function in oxazolidinone-treated megakaryoblastic cell lines.

Thrombocytopenia is commonly seen in patients receiving linezolid for >14 days. Linezolid is a reversible inhibitor of mitochondrial function in various cell types. This study investigated the inhibitory effects of linezolid and tedizolid, and their potential recovery on (i) CYTox I expression (subunit I of cytochrome c-oxidase; encoded by the mitochondrial genome), (ii) cytochrome c-oxidase activity and (iii) mitochondrial respiration (Seahorse bioanalysis) in two megakaryocytic cell lines [UT-7 WT (human acute megakaryoblastic leukaemia cells) and UT-7 MPL (transduced to express the thrombopoietin receptor)]. Cells were exposed to linezolid (0.5-25 mg/L) or tedizolid (0.1-5 mg/L) for up to 5 days and recovery followed after drug removal. Both oxazolidinones caused concentration- and time-dependent inhibition of CYTox I expression, cytochrome c-oxidase activity and mitochondrial spare capacity. On electron microscopy, mitochondria appeared dilated with a loss of cristae. Globally, tedizolid exerted stronger effects than linezolid. While CYTox I expression recovered completely after 6 days of drug washout, only partial (linezolid) or no (tedizolid) recovery of cytochrome c-oxidase activity, and no rescue of mitochondrial spare capacity (after 3 days) was observed. Thus, and in contrast to previous studies using a variety of cell lines unrelated to megakaryocytic lineages, the inhibitory effects exerted by oxazolidinones on the mitochondrial function of megakaryoblastic cells appear to be particularly protracted. Given the dynamics of platelet production and destruction, these results may explain why oxazolidinone-induced thrombocytopenia is one of the most common side effects in patients exposed to these antibiotics.