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Traditionally, tacrolimus is assessed in whole blood samples, but this is suboptimal from the perspective that erythrocyte-bound tacrolimus is not a good representative of the active fraction. In this work, a straightforward and rapid method was developed for determination of plasma tacrolimus in solid organ transplant recipients, using liquid chromatography tandem mass spectrometry (LC-MS/MS) with heated electrospray ionisation. Sample preparation was performed through protein precipitation of 200 µl plasma with 500 µl stable isotopically labelled tacrolimus I.S. in methanol, where 20 µl was injected on the LC-MS/MS system. Separation was done using a chromatographic gradient on a C18 column (50 × 2.1 mm, 2.6 µm). The method was linear in the concentration range 0.05–5.00 µg/L, with within-run and between-run precision in the range 2–6 % and a run time of 1.5 min. Furthermore, the method was validated for selectivity, sensitivity, carry-over, accuracy and precision, process efficiency, recovery, matrix effect, and stability following EMA and FDA guidelines. Clinical validation was performed in 2333 samples from 1325 solid organ transplant recipients using tacrolimus (liver n = 312, kidney n = 1714, and lung n = 307), which had median plasma tacrolimus trough concentrations of 0.10 µg/L, 0.15 µg/L and 0.23 µg/L, respectively. This method is suitable for measurement of tacrolimus in plasma and will facilitate ongoing observational and prospective studies on the relationship of plasma tacrolimus concentrations with clinical outcomes.

Background Early detection and correction of low fluoroquinolone exposure may improve treatment of MDR-TB. Objectives To explore a recently developed portable, battery-powered, UV spectrophotometer for measuring levofloxacin in saliva of people treated for MDR-TB. Methods Patients treated with levofloxacin as part of a regimen for MDR-TB in Northern Tanzania had serum and saliva collected concurrently at 1 and 4 h after 2 weeks of observed levofloxacin administration. Saliva levofloxacin concentrations were quantified in the field via spectrophotometry, while serum was analysed at a regional laboratory using HPLC. A Bayesian population pharmacokinetics model was used to estimate the area under the concentration–time curve (AUC0–24). Subtarget exposures of levofloxacin were defined by serum AUC0–24 Results Among 45 patients, 11 (25.6%) were women and 16 (37.2%) were living with HIV. Median AUC0–24 in serum was 140 (IQR = 102.4–179.09) mg·h/L and median AUC0–24 in saliva was 97.10 (IQR = 74.80–121.10) mg·h/L. A positive linear correlation was observed with serum and saliva AUC0–24, and a receiver operating characteristic curve constructed to detect serum AUC0–24 below 80 mg·h/L demonstrated excellent prediction [AUC 0.80 (95% CI = 0.62–0.94)]. Utilizing a saliva AUC0–24 cut-off of 91.6 mg·h/L, the assay was 88.9% sensitive and 69.4% specific in detecting subtarget serum AUC0–24 values, including identifying eight of nine patients below target. Conclusions Portable UV spectrophotometry as a point-of-care screen for subtarget levofloxacin exposure was feasible. Use for triage to other investigation or personalized dosing strategy should be tested in a randomized study.

IntroductionTherapeutic drug monitoring (TDM) for personalized dosing of fluoroquinolones has been recommended to optimize efficacy and reduce acquired drug resistance in the treatment of MDR TB. Therefore, the aim of this study was to develop a simple, low-cost, robust assay for TDM using mobile UV/visible light (UV/VIS) spectrophotometry to quantify levofloxacin in human saliva at the point of care for TB endemic settings.MethodsAll experiments were performed on a mobile UV/VIS spectrophotometer. The levofloxacin concentration was quantified by using the amplitude of the second-order spectrum between 300 and 400 nm of seven calibrators. The concentration of spiked samples was calculated from the spectrum amplitude using linear regression. The method was validated for selectivity, specificity, linearity, accuracy and precision. Drugs frequently co-administered were tested for interference.ResultsThe calibration curve was linear over a range of 2.5–50.0 mg/L for levofloxacin, with a correlation coefficient of 0.997. Calculated accuracy ranged from –5.2% to 2.4%. Overall precision ranged from 2.1% to 16.1%. Application of the Savitsky–Golay method reduced the effect of interferents on the quantitation of levofloxacin. Although rifampicin and pyrazinamide showed analytical interference at the lower limit of quantitation of levofloxacin concentrations, this interference had no implication on decisions regarding the levofloxacin dose.ConclusionsA simple UV/VIS spectrophotometric method to quantify levofloxacin in saliva using a mobile nanophotometer has been validated. This method can be evaluated in programmatic settings to identify patients with low levofloxacin drug exposure to trigger personalized dose adjustment.

Background In TB, therapeutic drug monitoring (TDM) is recommended for linezolid; however, implementation is challenging in endemic settings. Non-invasive saliva sampling using a mobile assay would increase the feasibility of TDM. Objectives To validate a linezolid saliva assay using a mobile UV spectrophotometer. Methods The saliva assay was developed using NanoPhotometer NP80® and linezolid concentrations were quantified using second-order derivative spectroscopy. Sample preparation involved liquid–liquid extraction of saliva, using saturated sodium chloride and ethyl acetate at 1:1:3 (v/v/v). The assay was validated for accuracy, precision, selectivity, specificity, carry-over, matrix effect, stability and filters. Acceptance criteria were bias and coefficient of variation (CV) Results Linezolid concentrations correlated with the amplitude between 250 and 270 nm on the second-order derivative spectra. The linezolid calibration curve was linear over the range of 3.0 to 25 mg/L (R2 = 0.99) and the LLOQ was 3.0 mg/L. Accuracy and precision were demonstrated with bias of −7.5% to 2.7% and CV ≤5.6%. The assay met the criteria for selectivity, matrix effect, carry-over, stability (tested up to 3 days) and use of filters (0.22 μM Millex®-GV and Millex®-GP). Specificity was tested with potential co-medications. Interferences from pyrazinamide, levofloxacin, moxifloxacin, rifampicin, abacavir, acetaminophen and trimethoprim were noted; however, with minimal clinical implications on linezolid dosing. Conclusions We validated a UV spectrophotometric assay using non-invasive saliva sampling for linezolid. The next step is to demonstrate clinical feasibility and value to facilitate programmatic implementation of TDM.

The persisting worldwide burden of tuberculosis (TB) is worrisome. In 2018, an estimated 10 million individuals developed TB and 1.45 million deceased [1]. The increase in drug resistance is an important point of concern. Resistance can be acquired by inappropriate drug management, non-compliance, and insufficient drug exposure [2, 3]. The last is frequently described for the first-line TB drugs rifampicin and isoniazid due to large inter-individual pharmacokinetic variability [3]. Therapeutic drug monitoring (TDM) can be used to verify drug exposure and adjust individual drug dosages if needed [4]. The efficacy of rifampicin and isoniazid is associated with the ratio of the steady-state area under the concentration-time curve from 0 to 24 h to minimal inhibitory concentration (AUC0–24/MIC) with a target value of >271 for rifampicin and >567 for isoniazid [5, 6]. Footnotes This manuscript has recently been accepted for publication in the European Respiratory Journal . It is published here in its accepted form prior to copyediting and typesetting by our production team. After these production processes are complete and the authors have approved the resulting proofs, the article will move to the latest issue of the ERJ online. Please open or download the PDF to view this article. Conflict of interest: Dr. van den Elsen has nothing to disclose. Conflict of interest: Dr. Akkerman has nothing to disclose. Conflict of interest: Dr. Wessels has nothing to disclose. Conflict of interest: Dr. Jongedijk has nothing to disclose. Conflict of interest: Dr. Ghimire has nothing to disclose. Conflict of interest: Dr. van der Werf has nothing to disclose. Conflict of interest: Dr. Bolhuis has nothing to disclose. Conflict of interest: Dr. Touw has nothing to disclose. Conflict of interest: Dr. Alffenaar has nothing to disclose.

Treatment of multidrug-resistant tuberculosis (MDR-TB) is challenging due to high treatment failure rate and adverse drug events. This study aimed to develop and validate a simple LC-MS/MS method for simultaneous measurement of five TB drugs in human plasma and to facilitate therapeutic drug monitoring (TDM) in MDR-TB treatment to increase efficacy and reduce toxicity. Moxifloxacin, levofloxacin, prothionamide, pyrazinamide and ethambutol were prepared in blank plasma from healthy volunteers and extracted using protein precipitation reagent containing trichloroacetic acid. Separation was achieved on an Atlantis T3 column with gradient of 0.1% formic acid in water and acetonitrile. Drug concentrations were determined by dynamic multiple reaction monitoring in positive ion mode on a LC-MS/MS system. The method was validated according to the United States' Food and Drug Administration (FDA) guideline for bioanalytical method validation. The calibration curves for moxifloxacin, levofloxacin, prothionamide, pyrazinamide and ethambutol were linear, with the correlation coefficient values above 0.993, over a range of 0.1-5, 0.4-40, 0.2-10, 2-100 and 0.2-10 mg/L, respectively. Validation showed the method to be accurate and precise with bias from 6.5% to 18.3% for lower limit of quantification and -5.8% to 14.6% for LOW, medium (MED) and HIGH drug levels, and with coefficient of variations within 11.4% for all levels. Regarding dilution integrity, the bias was within 7.2% and the coefficient of variation was within 14.9%. Matrix effect (95.7%-112.5%) and recovery (91.4%-109.7%) for all drugs could be well compensated by their isotope-labelled internal standards. A benchtop stability test showed that the degradation of prothionamide was over 15% after placement at room temperature for 72 h. Clinical samples (n = 224) from a cohort study were analyzed and all concentrations were within the analytical range. The signal of prothionamide was suppressed in samples with hemolysis which was solved by sample dilution. As the method is robust and sample preparation is simple, it can easily be implemented to facilitate TDM in programmatic MDR-TB treatment.

Aim: To develop a simple and robust LC–MS/MS method to quantify concentrations of micafungin in human plasma for pharmacokinetic studies and therapeutic drug monitoring. Methods: Sample preparation involved protein precipitation with acetonitrile:methanol (83:17% v/v) and [13C6]-micafungin as internal standard. A rapid and selective method for micafungin was validated across a range of 0.200–10.0 mg/l. Results: The calculated accuracy for the eight-point calibration ranged from 0.7 to 5.3%. Within-run precision ranged from 0.8 to 5.9%, between-run precision ranged from 0.7 to 3.1%, and overall precision ranged from 1.3 to 6.6%. Conclusion: A simple and robust LC–MS/MS method for analyzing micafungin in human plasma has been validated and was utilized for quantification of micafungin.

Therapeutic drug monitoring using saliva as matrix is a suitable alternative for serum therapeutic drug monitoring of linezolid, but not for moxifloxacin due to a high variability in saliva-plasma ratioshttp://bit.ly/2NIYdz7

Saliva may be a useful alternative matrix for monitoring levofloxacin concentrations in multidrug-resistant tuberculosis (MDR-TB) patients. The objectives of this study were (i) to evaluate the correlation between plasma and salivary levofloxacin (Lfx) concentrations in MDR-TB patients and (ii) to gauge the possibility of using saliva as an alternative sampling matrix for therapeutic drug monitoring of Lfx in areas where TB is endemic. This was a prospective pharmacokinetic study that enrolled MDR-TB patients receiving levofloxacin (750- to 1,000-mg once-daily dosing) under standardized treatment regimen in Nepal. Paired blood and saliva samples were collected at steady state. Lfx concentrations were quantified using liquid chromatography-tandem mass spectrometry. Pharmacokinetic parameters were calculated using noncompartmental kinetics. Lfx drug exposures were evaluated in 23 MDR-TB patients. During the first month, the median (interquartile range [IQR]) areas under the concentration-time curve from 0 to 24 h (AUC(0–24)) were 67.09 (53.93 to 98.37) mg ⋅ h/liter in saliva and 99.91 (76.80 to 129.70) mg ⋅ h/liter in plasma, and the saliva plasma (S/P) ratio was 0.69 (0.53 to 0.99). Similarly, during the second month, the median (IQR) AUC(0–24) were 75.63 (61.45 to 125.5) mg ⋅ h/liter in saliva and 102.7 (84.46 to 131.9) mg ⋅ h/liter in plasma, with an S/P ratio of 0.73 (0.66 to 1.18). Furthermore, large inter- and intraindividual variabilities in Lfx concentrations were observed. This study could not demonstrate a strong correlation between plasma and saliva Lfx levels. Despite a good Lfx penetration in saliva, the variability in individual saliva-to-plasma ratios limits the use of saliva as a valid substitute for plasma. Nevertheless, saliva could be useful in semiquantitatively predicting Lfx plasma levels. (This study has been registered at ClinicalTrials.gov under identifier NCT03000517.)

BACKGROUND: Dried blood spot (DBS) sampling is a blood collection tool that uses a finger prick to obtain a blood drop on a dried blood spot card. It can be used for therapeutic drug monitoring, a method that uses blood drug concentrations to optimize individual treatment. DBS sampling is thought to be a simpler way of blood collection compared to venous sampling. The aim of this study was to evaluate the quality of dried blood spots from tuberculosis patients all around the world based on quality indicators in a structured assessment procedure. METHODS: Total 464 DBS cards were obtained from four countries: Bangladesh, Belarus, Indonesia and Paraguay. The quality of the DBS cards was assessed using a checklist consisting of 19 questions divided into four categories: the integrity of the DBS materials, appropriate drying time, blood volume and blood spot collection. RESULTS: After examination, 859 of 1856 (46 %) blood spots did not comply with present quality criteria. In 625 cases (34%), this was due to incorrect blood spot collection. The DBS cards from Bangladesh, Indonesia and Paraguay seemed to be affected by air humidity, causing the blood spots not to dry appropriately. CONCLUSION: New tools to help obtain blood spots of sufficient quality are necessary as well as environmental specific recommendations in order to determine plasma-concentrations correctly. Additionally, 3% of the DBS cards were rejected because the integrity of the materials suggesting that the quality of plastic zip lock bags currently used to protect the DBS cards against contamination and humidity may not be sufficient.

50% of MDR-TB patients with higher MICs do not have enough Lfx exposure with currently prescribed once-daily dosing of 750–1000 mg. Therefore, it is suggested that MDR-TB patients should receive higher 1250–1500 mg Lfx dosages.http://ow.ly/ZQsN30nuNBx

Therapeutic drug monitoring (TDM) uses drug concentrations, primarily from plasma, to optimize drug dosing. Optimisation of drug dosing may improve treatment outcomes, reduce toxicity and reduce the risk of acquired drug resistance. The aim of this narrative review is to outline and discuss the challenges of developing multi-analyte assays for anti-tuberculosis (TB) drugs using liquid chromatography-tandem mass spectrometry (LC-MS/MS) by reviewing the existing literature in the field. Compared to other analytical methods, LC-MS/MS offers higher sensitivity and selectivity while requiring relatively low sample volumes. Additionally, multi-analyte assays are easier to perform since adequate separation and short run times are possible even when non-selective sample preparation techniques are used. However, challenges still exist, especially when optimizing LC separation techniques for assays that include analytes with differing chemical properties. Here, we have identified seven multi-analyte assays for first-line anti-TB drugs that use various solvents for sample preparation and mobile phase separation. Only two multi-analyte assays for second-line anti-TB drugs were identified (including either nine or 20 analytes), with each using different protein precipitation methods, mobile phases and columns. The 20 analyte assay did not include bedaquiline, delamanid, meropenem or imipenem. For these drugs, other assays with similar methodologies were identified that could be incorporated in the development of a future comprehensive multi-analyte assay. TDM is a powerful methodology for monitoring patient’s individual treatments in TB programmes, but its implementation will require different approaches depending on available resources. Since TB is most-prevalent in low- and middle-income countries where resources are scarce, a patient-centred approach using sampling methods other than large volume blood draws, such as dried blood spots or saliva collection, could facilitate its adoption and use. Regardless of the methodology of collection and analysis, it will be critical that laboratory proficiency programmes are in place to ensure adequate quality control. It is our intent that the information contained in this review will contribute to the process of assembling comprehensive multiplexed assays for the dynamic monitoring of anti-TB drug treatment in affected individuals.

Background: Dried blood spot (DBS) sampling for pharmacokinetic (PK) studies and therapeutic drug monitoring have unique advantages over venous sampling. This study aimed to evaluate a DBS method for first-line anti-tuberculosis drugs in children, and DBS sampling to assess PK parameters.Methods: Paraguayan children were treated according to the revised paediatric dosing scheme of the World Health Organization. A PK curve was performed both with DBS sampling and conventional venous sampling for rifampicin, pyrazinamide and ethambutol. Passing-Bablok regression, Bland-Altman plots and predictive performance evaluation were used to assess agreement between DBS and plasma concentrations. The percentages of patients attaining population PK values for C-max and AUC(0-24h) were calculated.Results: After use of a conversion factor, Passing-Bablok regression showed no significant proportional or systematic bias between DBS and plasma concentrations. Bland-Altman plots showed that 95% of the ratios of the DBS predicted:observed plasma concentrations lay between 0.6 and 1.4 for rifampicin, 0.5 and 1.6 for pyrazinamide and -0.4 and 2.8 for ethambutol. DBS measurements showed acceptable predictive performance for rifampicin and pyrazinamide, but not for ethambutol. Assessment of C-max target attainment was 62.5% for isoniazid, 25% for rifampicin, 100% for pyrazinamide and 75% for ethambutol.Conclusion: For rifampicin and pyrazinamide, the DBS method was accurate in predicting plasma concentrations, and was used successfully for PK parameter assessment. However, predicting ethambutol plasma concentrations with DBS measurement was associated with too much imprecision. Despite higher dosing, only 25% of the population reached average target adult rifampicin exposures. (C) 2018 Elsevier B.V. and International Society of Chemotherapy. All rights reserved.

Clinical studies on tuberculosis have shown a correlation between low drug exposure and treatment failure and acquired drug resistance. Objective was to develop a LC-MS/MS method for the quantification of isoniazid, pyrazinamide and ethambutol. Stable isotope-labelled isoniazid-D4 and ethambutol-D4 were used as internal standards. Protein binding of isoniazid, pyrazinamide and ethambutol was investigated and proved low. Therefore, sample preparation using ultrafiltration could be applied, resulting in linear calibration curves in the range of 0.2-8 mg/L for isoniazid and ethambutol and 2-80 mg/L for pyrazinamide. The method was validated according to the guidelines of the FDA.A fast, simple and reliable LC-MS/MS method has been developed for the simultaneous determination of isoniazid, pyrazinamide and ethambutol in human serum for therapeutic drug monitoring and pharmacokinetic studies.

The estimated attributable mortality rate for invasive candidiasis (IC) in the intensive care unit (ICU) setting varies from 30 to 40%. Physiological changes in critically ill patients may affect the distribution and elimination of micafungin, and therefore, dosing adjustments might be mandatory. The objective of this study was to determine the pharmacokinetic parameters of micafungin in critically ill patients and assess the probability of target attainment. Micafungin plasma concentrations were measured to estimate the pharmacokinetic properties of micafungin. MIC values for Candida isolates were determined to assess the probability of target attainment for patients. Data from 19 patients with suspected or proven invasive candidiasis were available for analysis. The median area under the concentration-time curve from 0 to 24 h at steady state (AUC 0–24 ) was 89.6 mg · h/liter (interquartile range [IQR], 75.4 to 113.6 mg · h/liter); this was significantly lower than the median micafungin AUC 0–24 values of 152.0 mg · h/liter (IQR, 136.0 to 162.0 mg · h/liter) and 134.0 mg · h/liter (IQR, 118.0 to 148.6 mg · h/liter) in healthy volunteers ( P = P = Candida isolates were susceptible to micafungin, with a median MIC of 0.016 mg/liter (IQR, 0.012 to 0.023 mg/liter). The median AUC 0–24 /MIC ratio was 5,684 (IQR, 4,325 to 7,578), and 3 of the 17 evaluable patients (17.6%) diagnosed with proven invasive candidiasis did not meet the AUC/MIC ratio target of 5,000. Micafungin exposure was lower in critically ill patients than in healthy volunteers. The variability in micafungin exposure in this ICU population could be explained by the patients' body weight. Our findings suggest that healthier patients (sequential organ failure assessment [SOFA] score of