Association of Lamotrigine Plasma Concentrations with Efficacy and Toxicity in Patients with Epilepsy: A Retrospective Study.

BACKGROUND: There is limited evidence to support the currently suggested lamotrigine (LTG) therapeutic reference range of 2.5-15 mg/L for the treatment of seizures. The objective of this study was to evaluate the association of LTG plasma concentrations with the efficacy and toxicity of the treatment in patients with epilepsy. METHODS: Patients whose LTG plasma concentration was measured between January 2013 and February 2022 were included. Efficacy was defined as seizure freedom for at least 6 months around the time of measured LTG concentration. Toxicity was defined as any LTG-related adverse drug effect documented in each patient's health record or when the reason for measuring the LTG concentration was toxicity. In addition, the dose-concentration relationship of LTG was assessed. RESULTS: In total, 549 concentrations from 259 patients with epilepsy were included. The most common reasons for therapeutic drug monitoring were suspected inefficacy (39%) and pregnancy (21%). The LTG plasma concentration was not associated with efficacy (adjusted odds ratio = 0.94; 95% confidence interval, 0.85-1.04). The LTG plasma concentration was positively associated with the incidence of toxicity after adjusting for age, sex, and number of antiepileptic drugs (odds ratio = 1.11; 95% confidence interval, 1.04-1.19). The daily dose had a significant linear correlation with the LTG plasma concentration (P < 0.001). CONCLUSIONS: The LTG plasma concentration was associated with toxicity, whereas no association with efficacy was found. A reference range of 2.5-10 mg/L may be considered to decrease the risk of toxicity while maintaining similar efficacy. Therapeutic drug monitoring may be useful when LTG-related toxicity is suspected and in cases of pharmacokinetic changes (eg, pregnancy and concomitant use of interacting drugs) that can influence the LTG plasma concentration.

Pharmacokinetic investigations of isavuconazole in paediatric cancer patients show reduced exposure of isavuconazole after opening capsules for administration via a nasogastric tube.

OBJECTIVES: To study the isavuconazole pharmacokinetics in a real-life paediatric cohort and confirm whether the isavuconazole exposures are within the adult exposure range. Furthermore, we are the first to describe unbound isavuconazole pharmacokinetics. METHODS: In this prospective, observational study, the isavuconazole dosing regimen was as follows (IV/oral/nasogastric tube): 5.4 mg/kg isavuconazole (maximum 200 mg/dose) three times daily on Days 1 and 2, followed by 5.4 mg/kg isavuconazole (maximum 200 mg/dose) once daily. At least one pharmacokinetic curve was assessed. Non-linear mixed effects modelling was used for analysis. Monte Carlo simulations were performed with the above mentioned maintenance dose for IV administrations and a weight band dosing regimen for oral/nasogastric tube administrations: I) <18 kg (100 mg daily); II) 18-37 kg (150 mg daily); III)>37 kg (200 mg daily). RESULTS: Seventeen paediatric patients with a median age of 9 years (range 1-17) and median weight of 26.0 kg (range 8.4-78.5) were evaluated. A two-compartment model describing linear pharmacokinetics of the unbound concentrations and saturable protein binding fitted the isavuconazole concentrations best. The absolute bioavailability of isavuconazole was 41.0% (95% CI: 32.4%-50.8%). The median (IQR) simulated exposures (AUC0-24h, SS) of the total isavuconazole concentrations after IV and oral/nasogastric tube administration were 87.7 mg·h/L (70.5-105.1) and 50.3 mg·h/L (39.0-62.4), respectively. The unbound isavuconazole fraction (unbound/total) ranged from 0.5% to 2.3%. CONCLUSIONS: This study revealed low bioavailability after nasogastric tube administration with opened capsules. Isavuconazole exposures were in the expected range following IV administration. Total and unbound isavuconazole pharmacokinetics were reported with a 5-fold range in the unbound fraction.

Sub-therapeutic trimethoprim and sulfamethoxazole plasma concentrations during continuous venovenous hemofiltration in a patient with COVID-19 and pulmonary Pneumocystis jirovecii co-infection: A case report.

OBJECTIVE: To investigate drug concentration of trimethoprim-sulfamethoxazole (TMP-SMX) using therapeutic drug monitoring (TDM) for severe Pneumocystis jirovecii (PJP) infection in a critically ill patient with COVID-19 receiving continuous venovenous hemofiltration treatment and regional citrate anticoagulation (RCA-CCVH). MATERIALS AND METHODS: A 72-year-old man with hypoxemic respiratory failure due to COVID-19 infection was admitted to the intensive care unit for invasive mechanical ventilation. The patient developed acute renal failure that required RCA-CVVH. Pulmonary co-infection with PJP was diagnosed, and a high TMP-SMX dose was initiated according to (inter)national guidelines with dose reduction after 3 days because of renal failure. Population pharmacokinetics were assessed for TMP and SMX as well as clearance by RCA-CVVH, volume of distribution, and time above threshold levels for measured plasma concentrations. RESULTS: During renal failure requiring RCA-CVVH, a corresponding dose reduction of TMP-SMX to 320/1,600 mg twice a day, according to current Dutch SWAB and Dutch Association of Hospital Pharmacists guidelines, resulted in unintended under-dosing with sub-therapeutic TMP-SMX concentrations. Pharmacokinetic modeling and dose adjustment of TMP-SMX to 640/3,200 mg 3 times daily resulted in steady-state TMP-SMX peak concentrations associated with efficacy against PJP. Hence, the patient was successfully weaned from the ventilator and discharged. CONCLUSION: We hypothesize that our new dose recommendation of 640/3,200 mg TMP-SMX 3 times daily is associated with an increased probability of critical patients being successfully liberated from mechanical weaning following PJP pneumonia and COVID-19 infection.

Optimization of a Quantitative Anti-Drug Antibodies against Infliximab Assay with the Liquid Chromatography-Tandem Mass Spectrometry: A Method Validation Study and Future Perspectives.

Monoclonal antibodies (mAbs), such as infliximab, are important treatment options for different diseases. Immunogenicity is a major risk, resulting in anti-drug antibodies (ADAs), being associated with adverse events and loss of response, influencing long-term outcomes. The development of ADAs against infliximab is primarily measured by immunoassays like radioimmunoassay (RIA). Although liquid chromatography-tandem mass spectrometry (LC-MS/MS) is increasingly utilized across different fields, this technique is currently not used for ADAs against infliximab measurements. Therefore, we developed the first LC-MS/MS method. Stable isotopically labeled infliximab antigen-binding fragments (SIL IFX F(ab')2) were used to bind and measure ADAs indirectly. Protein A magnetic beads were used to capture IgG, including ADAs, whereafter SIL IFX F(ab')2 was added for labeling. After washing, internal standard addition, elution, denaturation and digestion samples were measured by LC-MS/MS. Internal validation showed good linearity between 0.1 and 16 mg/L (R2 > 0.998). Sixty samples were used for cross-validation with RIA, and no significant difference between ADA concentrations was found. The methods had high correlation (R = 0.94, p < 0.001) and excellent agreement, intraclass correlation coefficient = 0.912 (95% confidence interval 0.858-0.947, p < 0.001). We present the first ADA against the infliximab LC-MS/MS method. The method is amendable for quantifying other ADAs, making it applicable as a template for future ADA methods.

Ion suppression, reduced long-term robustness and leakage current of the spray voltage during the ionization of trichloroacetic acid; a case study with a methylmalonic acid assay.

Sample clean-up with the protein precipitation solvent trichloroacetic acid (TCA), combined with a stable isotope labeled internal standard, is widely used for the analysis of endogenous and exogenous compounds in serum and plasma with liquid chromatography-tandem mass spectrometry (LC-MS/MS). During the application of an assay for methylmalonic acid (MMA), used for routine analysis in patient care, negative long-term side effects of TCA on assay performance were observed. Step-by-step extensive troubleshooting disclosed the limitations of using TCA in MS. After running over 2000 samples with the MMA assay over a course of one year, a black coating formed between the probe and the heater that was traced to the use of TCA. The MMA assay used a C18 column with an isocratic eluent of 95% water (0.1% formic acid) as starting condition, on which TCA was more retained than MMA. Next, concentrations of 2.2% TCA in the prepared serum or plasma sample caused a drop in spray voltage during ionization into the MS. This was caused by the strong acid properties of TCA, resulting in current loss of the spray voltage between the heated electrospray ionization (HESI) needle and the union holder, which had also a grounding function. Replacing the original metal HESI needle with a custom made fussed silica HESI needle or detaching the union from the union holder, eliminated the effect of the drop in spray voltage. In conclusion, TCA can seriously affect the long-term robustness by affecting the source of the MS. We recommend the use of a very low sample injection volume, and/or shifting the mobile phase to waste when TCA is eluting, when using TCA in LC-MS/MS analysis.

Clinical characteristics do not reliably identify non-adherence in patients with uncontrolled hypertension.

PURPOSE: Chemical adherence testing is a reliable method to assess adherence to antihypertensive drugs. However, it is expensive and has limited availability in clinical practice. To reduce the number and costs of chemical adherence tests, we aimed to develop and validate a clinical screening tool to identify patients with a low probability of non-adherence in patients with uncontrolled hypertension. MATERIALS AND METHODS: In 495 patients with uncontrolled hypertension referred to the University Medical Centre Utrecht (UMCU), the Netherlands, a penalised logistic regression model including seven pre-specified easy-to-measure clinical variables was derived to estimate the probability of non-adherence. Non-adherence was defined as not detecting at least one of the prescribed antihypertensive drugs in plasma or urine. Model performance and test characteristics were evaluated in 240 patients with uncontrolled hypertension referred to the Heartlands Hospital, United Kingdom. RESULTS: Prevalence of non-adherence to antihypertensive drugs was 19% in the UMCU and 44% in the Heartlands Hospital population. After recalibration of the model's intercept, predicted probabilities agreed well with observed frequencies. The c-statistic of the model was 0.63 (95%CI 0.53-0.72). Predicted probability cut-off values of 15%-22.5% prevented testing in 5%-15% of the patients, carrying sensitivities between 97% (64-100) and 90% (80-95), and negative predictive values between 74% (10-99) and 70% (50-85). CONCLUSION: The combination of seven clinical variables is not sufficient to reliably discriminate adherent from non-adherent individuals to safely reduce the number of chemical adherence tests. This emphasises the complex nature of non-adherence behaviour and thus the need for objective chemical adherence tests in patients with uncontrolled hypertension.

Quantification of emicizumab by mass spectrometry in plasma of people with hemophilia A: A method validation study.

Background: Emicizumab is a new treatment option for people with hemophilia A. Emicizumab was approved with a body-weight-based dosage regimen, without laboratory monitoring requirements. Guidelines, however, recommend measuring emicizumab concentrations when the presence of antidrug antibodies is suspected. Furthermore, drug monitoring can be useful in clinical decision making, in adherence checking, and for research purposes. Therefore, we developed a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for quantifying emicizumab. We performed a validation study on this LC-MS/MS method quantifying emicizumab in the plasma of people with hemophilia A. Methods: Sample preparation for LC-MS/MS analysis included ammonium sulfate protein precipitation and trypsin digestion. A signature peptide of emicizumab and a matching stable isotope-labeled internal standard were used to quantify emicizumab by LC-MS/MS analysis. Validation was performed in accordance with the "Guideline on Bioanalytical Method Validation" of the European Medicines Agency (EMA). The LC-MS/MS method was cross validated against a modified and calibrated (r 2 Diagnostics) one-stage clotting assay (OSA). Conclusions: The LC-MS/MS method demonstrated linearity over a wide range of emicizumab concentrations, far exceeding the concentrations observed in people with hemophilia A. Precision and accuracy were excellent, and all other validation parameters were also within the acceptance EMA criteria. Cross validation showed that the LC-MS/MS method and the OSA-based method can be used interchangeably for drug monitoring of emicizumab without the application of a correction factor.

Antiviral treatment with fluoxetine for rituximab-associated chronic echovirus 13 meningoencephalitis and myofasciitis.

BACKGROUND AND PURPOSE: Enterovirus infections pose a serious threat for patients with humoral deficiencies and may be lethal, whilst the efficacy of proposed treatment options such as corticosteroids, intravenous immunoglobulins and fluoxetine remains debated. METHODS: Viral clearance was investigated in a patient with rituximab-induced B-cell depletion and chronic echovirus 13 (E13) meningoencephalitis/myofasciitis in response to intravenous immunoglobulins and fluoxetine using sequential semi-quantitative E13 viral load measurements by real-time reverse transcription polymerase chain reaction. Fluoxetine concentrations in plasma and cerebrospinal fluid were determined by liquid chromatography mass spectrometry. RESULTS: Intravenous immunoglobulins appeared ineffective in this case of E13 infection, whereas virus clearance in cerebrospinal fluid was obtained after 167 days of oral fluoxetine. Since treatment with corticosteroids resulted in a flare of symptoms, rechallenge with viral load measurements was not attempted. CONCLUSION: In this report of a patient with rituximab-associated chronic echovirus 13 meningoencephalitis, viral clearance in response to single treatment options is assessed for the first time. Our observations further support the in vivo efficacy of fluoxetine against enteroviral infections. More research is needed to establish its efficacy in different enterovirus strains.

Fludarabine exposure predicts outcome after CD19 CAR T-cell therapy in children and young adults with acute leukemia.

The addition of fludarabine to cyclophosphamide as a lymphodepleting regimen prior to CD19 chimeric antigen receptor (CAR) T-cell therapy significantly improved outcomes in patients with relapsed/refractory (r/r) B-cell acute lymphoblastic leukemia (B-ALL). Fludarabine exposure, previously shown to be highly variable when dosing is based on body surface area (BSA), is a predictor for survival in allogeneic hematopoietic cell transplantation (allo-HCT). Hence, we hypothesized that an optimal exposure of fludarabine might be of clinical importance in CD19 CAR T-cell treatment. We examined the effect of cumulative fludarabine exposure during lymphodepletion, defined as concentration-time curve (AUC), on clinical outcome and lymphocyte kinetics. A retrospective analysis was conducted with data from 26 patients receiving tisagenlecleucel for r/r B-ALL. Exposure of fludarabine was shown to be a predictor for leukemia-free survival (LFS), B-cell aplasia, and CD19-positive relapse following CAR T-cell infusion. Minimal event probability was observed at a cumulative fludarabine AUCT0-∞ ≥14 mg*h/L, and underexposure was defined as an AUCT0-∞ <14 mg*h/L. In the underexposed group, the median LFS was 1.8 months, and the occurrence of CD19-positive relapse within 1 year was 100%, which was higher compared with the group with an AUCT0-∞ ≥14 mg*h/L (12.9 months; P < .001; and 27.4%; P = .0001, respectively). Furthermore, the duration of B-cell aplasia within 6 months was shorter in the underexposed group (77.3% vs 37.3%; P = .009). These results suggest that optimizing fludarabine exposure may have a relevant impact on LFS following CAR T-cell therapy, which needs to be validated in a prospective clinical trial.

Middle-up quantification of therapeutic monoclonal antibodies in human plasma with two dimensional liquid chromatography high resolution mass spectrometry: Adalimumab as a proof of principle.

Next generation human therapeutic monoclonal antibodies (t-mAbs) are harder to quantify with the widely used bottom-up tryptic digestion method. Due to their homology with endogenous immunoglobulins, there is a lack of unique and stable 'signature' peptides that can be targeted. Middle-up two dimensional liquid chromatography high resolution mass spectrometry (2D-LC-HRMS), targeting the entire light chain, was examined as an alternative. Adalimumab (ADM) was successfully quantified in human plasma after Melon® Gel sample purification, followed by orthogonal separation on a weak cation exchange (WCX) and reversed phase column. Charge and hydrophobicity were used to separate ADM from the polyclonal immunoglobulin background. HRMS with its high resolution and exact mass was able to isotopically resolve the ADM light chain and to provide another separation dimension on the basis of mass to charge ratio. Using the targeted single ion monitoring (T-SIM) with multiplex (MSX) option, three ADM light chain precursors, 2341.80, 2129.00, and 1951.68 m/z, and one internal standard precursor 2146.39 m/z, were measured simultaneously. The Melon® Gel sample purification was found to be very efficient in removing plasma proteins that would otherwise interfere with chromatographic separation and ionization. The linearity of the method for the analysis of ADM was excellent (R2=0.999) between 1 - 128 mg/L with an LLOQ signal to noise ratio (S/N) of 10. Within-run and between-run precision and accuracy were in concordance with the EMA guideline. Cross-validation of the 2D-LC-HRM method with the standard peptide LC-MS/MS method showed a good agreement (R2 = 0.86) between the methods. However, there was a bias present, possibly due to charge variant ADM formation over time. Since the presented 2D-LC-HRMS method is able to measure only the native form of ADM, it is able to provide a measure of the active form of ADM in patients.

A generic sample preparation method for the multiplex analysis of seven therapeutic monoclonal antibodies in human plasma or serum with liquid chromatography-tandem mass spectrometry.

Due to the increasing number of therapeutic monoclonal antibodies (mAbs) used in the clinic, there is an increasing need for robust analytical methods to quantify total mAb concentrations in human plasma for clinical studies and therapeutic drug monitoring. We developed an easy, rapid, and robust sample preparation method for liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. The method was validated for infliximab (IFX), rituximab (RTX), cetuximab (CTX), dupilumab (DPL), dinutuximab (DNX), vedolizumab (VDZ), and emicizumab (EMZ). Saturated ammonium sulfate (AS) was used to precipitate immunoglobulins in human plasma. After centrifugation, supernatant containing albumin was decanted, and the precipitated immunoglobulin fraction was re-dissolved in buffer containing 6M guanidine. This fraction was then completely denatured, reduced, alkylated, and trypsin digested. Finally, signature peptides from the seven mAbs were simultaneously quantified on LC-MS/MS together with their internal standards stable isotopically labeled peptide counterparts. The linear dynamic ranges (1 - 512 mg/L) of IFX, CTX, RTX, and EMZ showed excellent (R2 > 0.999) linearity and those of DPL, DNX, and VDZ showed good (R2 > 0.995) linearity. The method was validated in accordance with the EMA guidelines. EDTA plasma, sodium citrate plasma, heparin plasma, and serum yielded similar results. Prepared samples were stable at room temperature (20°C) and at 5°C for 3 days, and showed no decline in concentration for all tested mAbs. This described method, which has the advantage of an easy, rapid, and robust pre-analytical sample preparation, can be used as a template to quantify other mAbs in human plasma or serum.

Population pharmacokinetics of clofarabine for allogeneic hematopoietic cell transplantation in paediatric patients.

AIMS: Clofarabine has recently been evaluated as part of the conditioning regimen for allogeneic hematopoietic stem cell transplantation (HCT) in children. Pharmacokinetic (PK) exposure of different agents commonly used in conditioning regimens is strongly related to HCT outcome. Consequently, the PK of clofarabine may be important for outcome. This report describes the population PK of clofarabine in paediatric patients and one adult. METHODS: From 80 paediatric (0.5-18 years) and 1 adult patient (37 years), 805 plasma concentrations were included in pharmacokinetic analyses using nonlinear mixed effects modelling. RESULTS: A two-compartment model adequately described the PK of clofarabine. Body weight and estimated glomerular filtration rate (eGFR) were included as covariates. Clearance was differentiated into nonrenal and renal clearance (approximately 55% of total clearance), resulting in population estimates of 24.0 L/h (95% confidence interval [CI] 13.7-34.4) and 29.8 L/h (95% CI 23.9-36.1) for a patient of 70 kg with normal renal function, respectively. Unexplained interindividual variability in clearance was 17.8% (95% CI 14.6-22.4). A high variability in exposure was observed (range area under the curveT0-inf 1.8-6.0 mg/L*h) after body surface area (BSA) based dosing. Interestingly, children with low body weight had a lower exposure than children with a higher body weight, which indicates that the currently practised BSA-based dosing is not adequate for clofarabine. CONCLUSION: A clofarabine dosing algorithm based on this PK model, using body weight and eGFR, results in a more predictable exposure than BSA-based dosing. However, the exact target exposure needs to be further investigated.

Plasma Trough Concentrations of Antihypertensive Drugs for the Assessment of Treatment Adherence: A Meta-Analysis.

Biochemical drug screening by liquid chromatography-tandem mass spectrometry in plasma is an accurate method for the quantification of plasma concentrations of antihypertensive medications in patients with hypertension. Trough concentrations could possibly be used as drug-specific cutoff values in the biochemical assessment of (non-)adherence. We performed a literature review and meta-analysis of pharmacokinetic studies to determine plasma trough concentrations of amlodipine, hydrochlorothiazide, and valsartan. PubMed was searched for pharmacokinetic studies up to September 2020. Eligible studies reported steady-state mean trough concentration and their variance. Pooled trough concentrations were estimated using a three-level random effects meta-analytic model. Moderator analyses were performed to explore sources of heterogeneity. One thousand three hundred eighteen potentially relevant articles were identified of which 45 were eligible for inclusion. The pooled mean trough concentration was 9.2 ng/mL (95% CI, 7.5-10.8) for amlodipine, 41.0 ng/mL (95% CI, 17.4-64.7) for hydrochlorothiazide, and 352.9 ng/mL (95% CI, 243.5-462.3) for valsartan. Substantial heterogeneity was present for all 3 pooled estimates. Moderator analyses identified dosage as a significant moderator for the pooled trough concentration of amlodipine (ß1=0.9; P<0.05), mean age, and mean body weight for the mean trough concentration of hydrochlorothiazide (ß1=2.2, P<0.05, respectively, ß1=-4.0, P<0.05) and no significant moderators for valsartan. Plasma trough concentrations of amlodipine, hydrochlorothiazide, and valsartan, measured with liquid chromatography-tandem mass spectrometry, are highly heterogeneous over the different studies. Use of the pooled trough concentration as a cutoff in the biochemical assessment of adherence can result in inaccurate diagnosis of (non-)adherence, which may seriously harm the patient-physician relationship, and is therefore not recommended.

Caspofungin Weight-Based Dosing Supported by a Population Pharmacokinetic Model in Critically Ill Patients.

The objective of this study was to develop a population pharmacokinetic model and to determine a dosing regimen for caspofungin in critically ill patients. Nine blood samples were drawn per dosing occasion. Fifteen patients with (suspected) invasive candidiasis had one dosing occasion and five had two dosing occasions, measured on day 3 (±1) of treatment. Pmetrics was used for population pharmacokinetic modeling and probability of target attainment (PTA). A target 24-h area under the concentration-time curve (AUC) value of 98 mg·h/liter was used as an efficacy parameter. Secondarily, the AUC/MIC targets of 450, 865, and 1,185 were used to calculate PTAs for Candida glabrata, C. albicans, and C. parapsilosis, respectively. The final 2-compartment model included weight as a covariate on volume of distribution (V). The mean V of the central compartment was 7.71 (standard deviation [SD], 2.70) liters/kg of body weight, the mean elimination constant (Ke ) was 0.09 (SD, 0.04) h-1, the rate constant for the caspofungin distribution from the central to the peripheral compartment was 0.44 (SD, 0.39) h-1, and the rate constant for the caspofungin distribution from the peripheral to the central compartment was 0.46 (SD, 0.35) h-1 A loading dose of 2 mg/kg on the first day, followed by 1.25 mg/kg as a maintenance dose, was chosen. With this dose, 98% of the patients were expected to reach the AUC target on the first day and 100% of the patients on the third day. The registered caspofungin dose might not be suitable for critically ill patients who were all overweight (≥120 kg), over 80% of median weight (78 kg), and around 25% of lower weight (≤50 kg). A weight-based dose regimen might be appropriate for achieving adequate exposure of caspofungin in intensive care unit patients.

Low Caspofungin Exposure in Patients in Intensive Care Units.

In critically ill patients, drug exposure may be influenced by altered drug distribution and clearance. Earlier studies showed that the variability in caspofungin exposure was high in intensive care unit (ICU) patients. The primary objective of this study was to determine if the standard dose of caspofungin resulted in adequate exposure in critically ill patients. A multicenter prospective study in ICU patients with (suspected) invasive candidiasis was conducted in the Netherlands from November 2013 to October 2015. Patients received standard caspofungin treatment, and the exposure was determined on day 3 of treatment. An area under the concentration-time curve from 0 to 24 h (AUC0-24) of 98 mg · h/liter was considered adequate exposure. In case of low exposure (i.e., <79 mg · h/liter, a ≥20% lower AUC0-24), the caspofungin dose was increased and the exposure reevaluated. Twenty patients were included in the study, of whom 5 had a positive blood culture. The median caspofungin AUC0-24 at day 3 was 78 mg · h/liter (interquartile range [IQR], 69 to 97 mg · h/liter). A low AUC0-24 (<79 mg · h/liter) was seen in 10 patients. The AUC0-24 was significantly and positively correlated with the caspofungin dose in mg/kg/day (P = 0.011). The median AUC0-24 with a caspofungin dose of 1 mg/kg was estimated using a pharmacokinetic model and was 114.9 mg · h/liter (IQR, 103.2 to 143.5 mg · h/liter). In conclusion, the caspofungin exposure in ICU patients in this study was low compared with that in healthy volunteers and other (non)critically ill patients, most likely due to a larger volume of distribution. A weight-based dose regimen is probably more suitable for patients with substantially altered drug distribution. (This study has been registered at ClinicalTrials.gov under registration no. NCT01994096.).

Therapeutic Drug Monitoring of Posaconazole: an Update.

Posaconazole is a second-generation triazole agent with a potent and broad antifungal activity. In addition to the oral suspension, a delayed-release tablet and intravenous formulation with improved pharmacokinetic properties have been introduced recently. Due to the large interindividual and intraindividual variation in bioavailability and drug-drug interactions, therapeutic drug monitoring (TDM) is advised to ensure adequate exposure and improve clinical response for posaconazole. Here, we highlight and discuss the most recent findings on pharmacokinetics and pharmacodynamics of posaconazole in the setting of prophylaxis and treatment of fungal infections and refer to the challenges associated with TDM of posaconazole.

Subtherapeutic Posaconazole Exposure and Treatment Outcome in Patients With Invasive Fungal Disease.

BACKGROUND: Posaconazole exposure seems to be subtherapeutic in some patients with invasive fungal disease. Due to the pharmacokinetic variability of posaconazole, therapeutic drug monitoring may help to optimize the efficacy of this antifungal drug. METHODS: A retrospective study of patients treated with posaconazole from January 2008 to April 2014 and for whom posaconazole serum concentrations were available was conducted. Risk factors for underexposure of posaconazole were detected, and the relationship between posaconazole exposure and treatment outcome according to the European Organization for Research and Treatment of Cancer (EORTC) criteria was assessed. RESULTS: Seventy patients met the inclusion criteria, 45 patients received posaconazole as treatment, and 25 patients received posaconazole as a prophylactic. Posaconazole serum trough concentrations were <1.25 mg/L in 44.4% of patients receiving treatment and <0.7 mg/L in 40.0% of patients receiving prophylactic posaconazole. Multiple linear regression analysis showed a significant, independent, and negative association of the posaconazole serum trough concentration with a lack of enteral nutrition (P < 0.001), vomiting (P = 0.035), the use of a proton pump inhibitor or H2-receptor antagonist (P < 0.001), a liquid diet (P = 0.002), concomitant chemotherapy (P = 0.004), and a posaconazole dose frequency of 2 times daily (P = 0.015). A higher posaconazole concentration was associated with a better treatment outcome [odds ratio = 22.22 (95% confidence interval, 3.40-145.33); P = 0.001]. CONCLUSIONS: Posaconazole exposure is insufficient in more than 40% of patients at risk of or with invasive fungal disease, and posaconazole exposure is positively correlated with a successful treatment outcome. Therapeutic drug monitoring of posaconazole can detect underexposure and can be helpful in treatment optimization.

Clinical validation of the analysis of fluconazole in oral fluid in hospitalized children.

Fluconazole is a first-line antifungal agent for the treatment and prophylaxis of invasive candidiasis in pediatric patients. Pediatric patients are at risk of suboptimal drug exposure, due to developmental changes in gastrointestinal and renal function, metabolic capacity, and volume of distribution. Therapeutic drug monitoring (TDM) can therefore be useful to prevent underexposure of fluconazole in children and infants. Children, however, often fear needles and can have difficult vascular access. The purpose of this study was to develop and clinically validate a method of analysis to determine fluconazole in oral fluid in pediatric patients. Twenty-one paired serum and oral fluid samples were obtained from 19 patients and were analyzed using a validated liquid chromatography-tandem mass spectrometry (LC-MS-MS) method after cross-validation between serum and oral fluid. The results were within accepted ranges for accuracy and precision, and samples were stable at room temperature for at least 17 days. A Pearson correlation test for the fluconazole concentrations in serum and oral fluid showed a correlation coefficient of 0.960 (P < 0.01). The mean oral fluid-to-serum concentration ratio was 0.99 (95% confidence interval [CI], 0.88 to 1.10) with Bland-Altman analysis. In conclusion, an oral fluid method of analysis was successfully developed and clinically validated for fluconazole in pediatric patients and can be a noninvasive, painless alternative to perform TDM of fluconazole when blood sampling is not possible or desirable. When patients receive prolonged courses of antifungal treatment and use fluconazole at home, this method of analysis can extend the possibilities of TDM for patients at home.

Insufficient fluconazole exposure in pediatric cancer patients and the need for therapeutic drug monitoring in critically ill children.

BACKGROUND: Fluconazole is recommended as first-line treatment in invasive candidiasis in children and infants. Although timely achievement of adequate exposure of fluconazole improves outcome, therapeutic drug monitoring is currently not recommended. METHODS: We conducted a retrospective study of critically ill children treated with fluconazole from January 2007 to October 2013 and for whom fluconazole concentrations were available. We collected demographic, clinical, and treatment data through review of the medical records and determined the correlation of clinical variables with the fluconazole concentration. Additionally, we assessed the relation between the fluconazole concentration and the time to culture conversion in patients with proven invasive candidiasis. RESULTS: In total, 99 pediatric patients met the inclusion criteria. The fluconazole concentration was considered subtherapeutic in 40% of the patients. Multiple linear regression analysis showed a significant, independent, and positive association of the fluconazole trough concentration with the fluconazole dose (P <.001), weight (P = .009), and the serum urea concentration (P = .003), and a significant, independent, and negative association with age (P = .004) and cancer as an underlying condition (P = .003). A higher fluconazole concentration was associated with a shorter time to culture conversion (hazard ratio = 1.076 [95% confidence interval, 1.017-1.138]; P = .011). CONCLUSIONS: The fluconazole concentration is not sufficient in pediatric cancer patients with the currently recommended dose regimen, and a higher fluconazole dose is required to achieve adequate drug exposure. Therapeutic drug monitoring of fluconazole can be a valuable tool to detect possible underexposure in critically ill children.