Introduction: Broad-spectrum beta-lactams are commonly prescribed for empirical or selective treatment of bacterial infections in children with malignancies. In the immunocompromised, appropriate concentration exposure is crucial to ensure antimicrobial efficacy. Augmented renal clearance (ARC) is increasingly recognized in this population, and raises concern for unmet concentration targets. We conducted a retrospective evaluation of meropenem and piperacillin exposure in our hospital's pediatric hematology-oncology patients. Materials and Methods: We compared trough levels of meropenem and piperacillin in a cohort of unselected pediatric hematology-oncology patients stratified based on their estimated renal function as decreased, normal or with ARC, and on their neutrophil count. Results: Thirty-two children provided a total of 51 meropenem and 76 piperacillin samples. On standard intermittent intravenous regimen, 67% of all trough plasma concentrations were below targeted concentrations. In neutropenic children with bacterial infection, all meropenem and 60% of piperacillin levels were below target. Nearly two-thirds of total samples came from children with ARC. In these patients, antimicrobial exposure was insufficient in 85% of cases (compared to 36% in the decreased or normal renal function groups), despite a dosage sometimes exceeding the maximum recommended daily dose. Under continuous infusion of piperacillin, only 8% of plasma levels were insufficient. Discussion: Intermittent administration of meropenem and piperacillin often fails to ensure sufficient concentration exposure in children treated for malignancies, even at maximal recommended daily dosage. This can in part be attributed to ARC. We recommend thorough assessment of renal function, resolute dosage adjustment, continuous infusion whenever possible and systematic therapeutic drug monitoring.

Introduction: Broad-spectrum beta-lactams are commonly prescribed for empirical or selective treatment of bacterial infections in children with malignancies. In the immunocompromised, appropriate concentration exposure is crucial to ensure antimicrobial efficacy. Augmented renal clearance (ARC) is increasingly recognized in this population, and raises concern for unmet concentration targets. We conducted a retrospective evaluation of meropenem and piperacillin exposure in our hospital's pediatric hematology-oncology patients. Materials and Methods: We compared trough levels of meropenem and piperacillin in a cohort of unselected pediatric hematology-oncology patients stratified based on their estimated renal function as decreased, normal or with ARC, and on their neutrophil count. Results: Thirty-two children provided a total of 51 meropenem and 76 piperacillin samples. On standard intermittent intravenous regimen, 67% of all trough plasma concentrations were below targeted concentrations. In neutropenic children with bacterial infection, all meropenem and 60% of piperacillin levels were below target. Nearly two-thirds of total samples came from children with ARC. In these patients, antimicrobial exposure was insufficient in 85% of cases (compared to 36% in the decreased or normal renal function groups), despite a dosage sometimes exceeding the maximum recommended daily dose. Under continuous infusion of piperacillin, only 8% of plasma levels were insufficient. Discussion: Intermittent administration of meropenem and piperacillin often fails to ensure sufficient concentration exposure in children treated for malignancies, even at maximal recommended daily dosage. This can in part be attributed to ARC. We recommend thorough assessment of renal function, resolute dosage adjustment, continuous infusion whenever possible and systematic therapeutic drug monitoring.

ObjectiveAnti-tuberculosis (antiTB) drugs are characterized by an important inter-interindividual pharmacokinetic variability poorly predictable from individual patients’ characteristics. Therapeutic drug monitoring (TDM) may therefore be beneficial for patients with Mycobacterium tuberculosis infection, especially for the management of multidrug/extensively drug resistant- (MDR/XDR)-TB. Our objective was to develop robust HPLC-MS/MS methods for plasma quantification of 15 antiTB drugs and 2 metabolites, namely rifampicin, isoniazid plus N-acetyl-isoniazid, pyrazinamide, ethambutol (the conventional quadritherapy for susceptible TB) as well as combination of agents against MDR/XDR-TB: bedaquiline, clofazimine, delamanid and its metabolite M1, levofloxacin, linezolid, moxifloxacin, pretomanid, rifabutin, rifapentine, sutezolid, and cycloserine.MethodsPlasma protein precipitation was used for all analytes except cycloserine, which was analyzed separately after derivatization with benzoyl chloride. AntiTB quadritherapy drugs (Pool1) were separated by Hydrophilic Interaction Liquid Chromatography (column Xbridge BEH Amide, 2.1 × 150 mm, 2.5 μm, Waters®) while MDR/XDR-TB agents (Pool 2) and cycloserine (as benzoyl derivative) were analyzed by reverse phase chromatography on a column XSelect HSS T3, 2.1 × 75 mm, 3.5 µm (Waters®). All runs last <7 min. Quantification was performed by selected reaction monitoring electrospray tandem mass spectrometry, using stable isotopically labelled internal standards.ResultsThe method covers the clinically relevant plasma levels and was extensively validated based on FDA recommendations, with intra- and inter-assay precision (CV) < 15% over the validated ranges. Application of the method is illustrated by examples of TDM for two patients treated for drug-susceptible- and MDR-TB.ConclusionSuch convenient extraction methods and the use of stable isotope-labelled drugs as internal standards provide an accurate and precise quantification of plasma concentrations of all major clinically-used antiTB drugs regimens and is optimally suited for clinically efficient TDM against tuberculosis.

Objective: Unpredictable pharmacokinetics of antibiotics in patients with life-threatening bacterial infections is associated with drug under- or overdosing. Therapeutic drug monitoring (TDM) may guide dosing adjustment aimed at maximizing antibacterial efficacy and minimizing toxicity. Rapid and accurate analytical methods are key for real-time TDM. Our objective was to develop a robust high-performance liquid chromatography-tandem mass spectrometry method (HPLC-MS/MS) for multiplex quantification of plasma concentrations of 12 antibiotics: imipenem/cilastatin, meropenem, ertapenem, cefepime, ceftazidime, ceftriaxone, piperacillin/tazobactam, amoxicillin, flucloxacillin, rifampicin, daptomycin. Methods: A single extraction procedure consisting in methanol plasma protein precipitation and H2O dilution was used for all analytes. After chromatographic separation on an Acquity UPLC HSS-T3 2.1 x 50 mm, 1.8 mu m (Waters (R)) column, quantification was performed by electro-spray ionisation-triple quadrupole mass spectrometry with selected reaction monitoring detection. Antibiotics were divided in two pools of calibration according to the frequency of analyses requests in the hospital routine antibiotic TDM program. Stable isotopicallylabelled analogues were used as internal standards. A single analytical run lasted less than 9 min. Results: The method was validated based on FDA recommendations, including assessment of extraction yield (96-113.8%), matrix effects, and analytical recovery (86.3-99.6%). The method was sensitive (lower limits of quantification 0.02-0.5 mu g/mL), accurate (intra/inter-assay bias - 11.3 to +12.7%) and precise (intra/interassay CVs 2.1-11.5%) over the clinically relevant plasma concentration ranges (upper limits of quantification 20-160 mu g/mL). The application of the TDM assay was illustrated with clinical cases that highlight the impact on patients' management of an analytical assay providing information with short turn-around time on antibiotic plasma concentration. Conclusion: This simple, robust high-throughput multiplex HPLC-MS/MS assay for simultaneous quantification of plasma concentrations of 12 daily used antibiotics is optimally suited for clinically efficient real-time TDM.

Background Broad-spectrum beta-lactams such as meropenem (MER) and piperacillin-tazobactam (PIP) are commonly prescribed in children with cancer having febrile neutropenia. They are introduced at intensive dosage, unless decreased renal function calls for dose reduction. Recently, glomerular hyperfiltration (HF) was recognized to be frequent among children with cancer during initial cycles of chemotherapy.1 We evaluated the impact of HF on therapeutic exposure to MER and PIP. Methods We retrieved retrospectively all MER and PIP plasma levels measured in children with cancer in our hospital between 2012 and 2018. We compared trough levels with usual therapeutic ranges (derived from reference values of minimum inhibitory concentrations). We classified the children according to plasma creatinine and estimated glomerular filtration rate (Schwartz formula) as either altered-normal (< 160 mL/min/1.73 m2) or increased (i.e. HF, ≥160). Neutropenia was defined as absolute neutrophil count < 500 cells/µL. Results We collected 120 concentration values (53 MER, 67 PIP) measured in 50 children with cancer. Among them, 74 (62%) had concomitant creatinine values suggestive of HF, and 80 (67%) were neutropenic. Overall, 67% of trough levels were below usual therapeutic ranges (MER: 2–8 mg/L, PIP 8–30 mg/L). This was more often the case in presence of concomitant HF (MER: 92%, PIP: 83%), often associated with neutropenia. Low exposure was observed not only at initial intensive dosage (MER: 120 mg/kg/day, PIP: 400 mg/kg/day)2 but tended to persist despite dosage readjustment based on concentration monitoring. Moreover, bacteremia was diagnosed in 38 cases. Conclusion Current recommended doses of MER and PIP do not provide optimal concentration coverage throughout the dosing interval in a large fraction of children with cancer and febrile neutropenia as a result of HF. Monitoring of beta-lactams should be offered to all children with cancer to ensure best therapeutic success and avoid the development of resistance. References Kwatra NS, Meany HJ, Ghelani SJ, Zahavi D, Pandya N, Majd M. Glomerular hyperfiltration in children with cancer: prevalence and a hypothesis. Pediatr Radiol 2017;47(2):221–226. The Lexicomp Pediatric & Neonatal Dosage Handbook, 21st edition, Lexicomp, USA. Disclosure(s) Nothing to disclose

Background Broad-spectrum beta-lactams such as meropenem (MER) and piperacillin-tazobactam (PIP) are commonly prescribed in children with cancer having febrile neutropenia. They are introduced at intensive dosage, unless decreased renal function calls for dose reduction. Recently, glomerular hyperfiltration (HF) was recognized to be frequent among children with cancer during initial cycles of chemotherapy.1 We evaluated the impact of HF on therapeutic exposure to MER and PIP. Methods We retrieved retrospectively all MER and PIP plasma levels measured in children with cancer in our hospital between 2012 and 2018. We compared trough levels with usual therapeutic ranges (derived from reference values of minimum inhibitory concentrations). We classified the children according to plasma creatinine and estimated glomerular filtration rate (Schwartz formula) as either altered-normal (< 160 mL/min/1.73 m2) or increased (i.e. HF, ≥160). Neutropenia was defined as absolute neutrophil count < 500 cells/µL. Results We collected 120 concentration values (53 MER, 67 PIP) measured in 50 children with cancer. Among them, 74 (62%) had concomitant creatinine values suggestive of HF, and 80 (67%) were neutropenic. Overall, 67% of trough levels were below usual therapeutic ranges (MER: 2–8 mg/L, PIP 8–30 mg/L). This was more often the case in presence of concomitant HF (MER: 92%, PIP: 83%), often associated with neutropenia. Low exposure was observed not only at initial intensive dosage (MER: 120 mg/kg/day, PIP: 400 mg/kg/day)2 but tended to persist despite dosage readjustment based on concentration monitoring. Moreover, bacteremia was diagnosed in 38 cases. Conclusion Current recommended doses of MER and PIP do not provide optimal concentration coverage throughout the dosing interval in a large fraction of children with cancer and febrile neutropenia as a result of HF. Monitoring of beta-lactams should be offered to all children with cancer to ensure best therapeutic success and avoid the development of resistance. References Kwatra NS, Meany HJ, Ghelani SJ, Zahavi D, Pandya N, Majd M. Glomerular hyperfiltration in children with cancer: prevalence and a hypothesis. Pediatr Radiol 2017;47(2):221–226. The Lexicomp Pediatric & Neonatal Dosage Handbook, 21st edition, Lexicomp, USA. Disclosure(s) Nothing to disclose

BackgroundBroad-spectrum beta-lactams such as meropenem (MER) and piperacillin-tazobactam (PIP) are commonly prescribed in children with cancer having febrile neutropenia. They are introduced at intensive dosage, unless decreased renal function calls for dose reduction. Recently, glomerular hyperfiltration (HF) was recognized to be frequent among children with cancer during initial cycles of chemotherapy.1 We evaluated the impact of HF on therapeutic exposure to MER and PIP.MethodsWe retrieved retrospectively all MER and PIP plasma levels measured in children with cancer in our hospital between 2012 and 2018. We compared trough levels with usual therapeutic ranges (derived from reference values of minimum inhibitory concentrations). We classified the children according to plasma creatinine and estimated glomerular filtration rate (Schwartz formula) as either altered-normal (< 160 mL/min/1.73 m2) or increased (i.e. HF, ≥160). Neutropenia was defined as absolute neutrophil count < 500 cells/µL.ResultsWe collected 120 concentration values (53 MER, 67 PIP) measured in 50 children with cancer. Among them, 74 (62%) had concomitant creatinine values suggestive of HF, and 80 (67%) were neutropenic. Overall, 67% of trough levels were below usual therapeutic ranges (MER: 2–8 mg/L, PIP 8–30 mg/L). This was more often the case in presence of concomitant HF (MER: 92%, PIP: 83%), often associated with neutropenia. Low exposure was observed not only at initial intensive dosage (MER: 120 mg/kg/day, PIP: 400 mg/kg/day)2 but tended to persist despite dosage readjustment based on concentration monitoring. Moreover, bacteremia was diagnosed in 38 cases.ConclusionCurrent recommended doses of MER and PIP do not provide optimal concentration coverage throughout the dosing interval in a large fraction of children with cancer and febrile neutropenia as a result of HF. Monitoring of beta-lactams should be offered to all children with cancer to ensure best therapeutic success and avoid the development of resistance.ReferencesKwatra NS, Meany HJ, Ghelani SJ, Zahavi D, Pandya N, Majd M. Glomerular hyperfiltration in children with cancer: prevalence and a hypothesis. Pediatr Radiol 2017;47(2):221–226.The Lexicomp Pediatric & Neonatal Dosage Handbook, 21st edition, Lexicomp, USA.Disclosure(s)Nothing to disclose

Liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) constitutes now a key instrumental component of medical laboratory centres and has greatly facilitated the development of a considerable number of drugs assays for Therapeutic Drug Monitoring (TDM). The concept of TDM implies the measurement of concentrations of certain drugs in patients' blood, followed by dosage individualization based on patients' circulating exposure, targeting a pre-defined concentration range. This approach aims at increasing the likelihood of achieving therapeutic efficacy, while reducing the risk of toxicity. TDM can contribute to the rational individualization of critical drug treatments, notably antivirals, antibiotics, antiepileptics, psychotropic drugs and targeted anticancer agents, in the context of growing efforts towards personalized medicine. This article aims at reviewing the basic concepts, the role and the perspectives of evolution of TDM. It presents selected examples of clinical applications and gives some insights on how TDM is definitely benefiting from the tremendous development of LC-MS/MS techniques.