Simultaneous determination of trimethoprim and sulfamethoxazole in dried plasma and urine spots

Biological Fluid Microsampling for Therapeutic Drug Monitoring: A Narrative Review

Therapeutic drug monitoring (TDM) is a specialized area of laboratory medicine which involves the measurement of drug concentrations in biological fluids with the aim of optimizing efficacy and reducing side effects, possibly modifying the drug dose to keep the plasma concentration within the therapeutic range. Plasma and/or whole blood, usually obtained by venipuncture, are the "gold standard" matrices for TDM. Microsampling, commonly used for newborn screening, could also be a convenient alternative to traditional sampling techniques for pharmacokinetics (PK) studies and TDM, helping to overcome practical problems and offering less invasive options to patients. Although technical limitations have hampered the use of microsampling in these fields, innovative techniques such as 3-D dried blood spheroids, volumetric absorptive microsampling (VAMS), dried plasma spots (DPS), and various microfluidic devices (MDS) can now offer reliable alternatives to traditional samples. The application of microsampling in routine clinical pharmacology is also hampered by the need for instrumentation capable of quantifying analytes in small volumes with sufficient sensitivity. The combination of microsampling with high-sensitivity analytical techniques, such as liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS), is particularly effective in ensuring high accuracy and sensitivity from very small sample volumes. This manuscript provides a critical review of the currently available microsampling devices for both whole blood and other biological fluids, such as plasma, urine, breast milk, and saliva. The purpose is to provide useful information in the scientific community to laboratory personnel, clinicians, and researchers interested in implementing the use of microsampling in their routine clinical practice.

In-vial dried urine spot collection and processing for quantitative analyses

Analysis of dried urine spots (DUSs) is becoming an emerging technique in clinical, toxicological, and forensic chemistry due to the fully non-invasive collection, facile transportation, and simple storage of DUS samples. Correct DUS collection and elution is of the utmost importance because inadequate DUS sampling/processing may have direct consequences on quantitative DUS analyses and these aspects were, for the first time, comprehensively investigated in this contribution. Various groups of endogenous and exogenous species were selected as model analytes and their concentrations were monitored in DUSs collected on standard cellulose-based sampling cards. Strong chromatographic effects were observed for most analytes having a crucial impact on their distribution within the DUSs during sampling. Concentrations of target analytes were up to 3.75-fold higher in the central DUS sub-punch in comparison to the liquid urine. Consequently, substantially reduced concentrations of these analytes were determined in peripheral DUS sub-punches demonstrating that sub-punching, often applied to dried material spots, is not acceptable for quantitative DUS analyses. Hence, a simple, rapid, and user-friendly procedure was suggested, which employed an in-vial collection of a known urine volume on a pre-punched sampling disc (using a low-cost micropipette designed for patient-centric clinical sampling) and in-vial processing of the whole DUS. Excellent accuracy (0.20%) and precision (0.89%) of liquid transfers were achieved by the micropipette, which was also applied to remote DUS collection by laic and expert users. The resulting DUS eluates were analysed by capillary electrophoresis (CE) for the determination of endogenous urine species. The CE results demonstrated no significant differences between the two user groups, elution efficiencies of 88-100% (in comparison to the liquid urine), and precision better than 5.5%.

Potential use of a dried saliva spot (DSS) in therapeutic drug monitoring and disease diagnosis

In recent years, scientific researchers have increasingly become interested in noninvasive sampling methods for therapeutic drug monitoring and disease diagnosis. As a result, dried saliva spot (DSS), which is a sampling technique for collecting dried saliva samples, has been widely used as an alternative matrix to serum for the detection of target molecules. Coupling the DSS method with a highly sensitive detection instrument improves the efficiency of the preparation and analysis of biological samples. Furthermore, dried blood spots, dried plasma spots, and dried matrix spots, which are similar to those of the DSS method, are discussed. Compared with alternative biological fluids used in dried spot methods, including serum, tears, urine, and plasma, saliva has the advantage of convenience in terms of sample collection from children or persons with disabilities. This review aims to provide integral strategies and guidelines for dried spot methods to analyze biological samples by illustrating several dried spot methods. Herein, we summarize recent advancements in DSS methods from June 2014 to March 2021 and discuss the advantages and disadvantages of the key aspects of this method, including sample preparation and method validation. Finally, we outline the challenges and prospects of such methods in practical applications.

Current development of bioanalytical sample preparation techniques in pharmaceuticals

Sample preparation is considered as the bottleneck step in bioanalysis because each biological matrix has its own unique challenges and complexity. Competent sample preparation to extract the desired analytes and remove redundant components is a crucial step in each bioanalytical approach. The matrix effect is a key hurdle in bioanalytical sample preparation, which has gained extensive consideration. Novel sample preparation techniques have advantages over classical techniques in terms of accuracy, automation, ease of sample preparation, storage, and shipment and have become increasingly popular over the past decade. Our objective is to provide a broad outline of current developments in various bioanalytical sample preparation techniques in chromatographic and spectroscopic examinations. In addition, how these techniques have gained considerable attention over the past decade in bioanalytical research is mentioned with preferred examples. Modern trends in bioanalytical sample preparation techniques, including sorbent-based microextraction techniques, are primarily emphasized.

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Bioanalytical sampling techniques are described with suitable applications in pharmaceuticals.

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The pros and cons of each bioanalytical sampling techniques are described.

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Relevant biological matrices are outlined.

Quantification of Serum Sulfamethoxazole and Trimethoprim by Ultra-fast Solid-Phase Extraction-Tandem Mass Spectrometry

BACKGROUND

The combination of trimethoprim (TMP) and sulfamethoxazole (SMX) is used to treat a number of bacterial infections. TMP/SMX concentrations in serum are conventionally monitored using high-performance liquid chromatography (HPLC) or liquid chromatography tandem mass spectrometry. These methods require laborious manual extraction techniques and relatively long sample analysis times, necessitating the development of a simple, high-throughput method. A simple, high-throughput method to measure TMP/SMX using ultra-fast solid-phase extraction (SPE)-tandem mass spectrometry has been developed.

METHODS

Calibration standards, quality control materials, and patient samples were precipitated with acetonitrile containing isotopically labeled internal standards. Samples were vortexed, centrifuged for 5 minutes at 2053g, and the resulting supernatant was diluted in aqueous mobile phase and injected onto the C18 SPE cartridge. MS/MS analysis was performed by electrospray ionization in positive ion mode at a rate of <20 seconds per sample. A 5-point linear 1/x calibration curve was used to calculate sample concentrations.

RESULTS

The intra-assay precision coefficients of variation were <6% and <7% for SMX and TMP, respectively, and <10% for both interassay precision coefficients of variation. Comparison studies using 50 patient and spiked serum samples showed r values of 0.9890 and 0.9853 and y-intercept values of -1.918 and -1.357, respectively compared with the HPLC reference method. All data points were <±15% of the mean. Linearity [r = 0.9952 (SMX) and 0.9954 (TMP)] was established from 12 to 400 mcg/mL with a detection limit of 0.47 mcg/mL, and 1.2-40 mcg/mL with a detection limit of 0.06 mcg/mL, for SMX and TMP, respectively. For either drug, no significant carryover was observed after samples at the upper limit of quantification. No interference was observed from any of the 77 drugs and respective metabolites tested.

CONCLUSIONS

A high-throughput SPE-tandem mass spectrometry method for TMP/SMX quantification was developed. The <20 seconds analysis time is a significant improvement compared with traditional HPLC and liquid chromatography tandem mass spectrometry methods, without sacrificing analytical performance.

Dried Plasma Spots and Oral Fluid as Alternative Matrices for Therapeutic Drug Monitoring of Busulfan: Analytical Method Development and Clinical Evaluation

BACKGROUND

Busulfan (BU) is an alkylating agent with a narrow therapeutic index and high intraindividual pharmacokinetic variability used in conditioning therapy for hematopoietic stem cell transplantation. Monitoring BU exposure during high-dose conditioning regimens is recommended and positively impacts outcomes. We aimed to develop, validate, and apply a ultra-high-performance liquid chromatography-mass spectrometry (MS)/MS assay to measure BU concentrations in oral fluid and dried plasma spots (DPS) as alternative matrices to plasma.

METHODS

We prepared plasma and oral fluid samples by protein precipitation and DPS after liquid extraction. We analyzed extracts using an LC-MS/MS system with an Acquity HSS T3 column in the positive electrospray ionization mode. The method was validated and applied to 79 paired plasma and oral fluid samples from 7 patients on BU conditioning treatment. DPS were prepared by pipetting plasma onto Whatman 903 paper. The correlation between BU in plasma, oral fluid, and DPS samples was evaluated.

RESULTS

Run time was 4.0 minutes. The assay was linear at 50-5000 ng mL-1 (r > 0.99), precise (1.9%-5.3% oral fluid and 1.8%-5.9% DPS), and accurate (98.1%-108.9% oral fluid and 93%-103.1% DPS). BU was stable in DPS at 23°C for 24 hours. BU levels in oral fluid (r = 0.927) and DPS (r = 0.982) were significantly correlated with plasma. Despite the good correlation, we found a wide variation between oral fluid and plasma levels. The area under curves (AUCs) calculated with oral fluid concentrations were 79.1%-167.1% of plasma AUCs. Bland-Altman plots found a better agreement for DPS, with AUCs estimated from corrected DPS levels at 83.1%-114.1% of plasma values.

CONCLUSIONS

We developed and validated a simple and fast ultra-high-performance liquid chromatography-MS/MS assay to measure BU in oral fluid and DPS. The results do not support the use of oral fluid as a matrix for routine therapeutic drug monitoring of BU. The AUC estimated from BU measurements in DPS was comparable to that in plasma, supporting the use of DPS in BU therapeutic drug monitoring as an alternative matrix, with adequate short-term stability and logistic advantages.

A review of recent advances in microsampling techniques of biological fluids for therapeutic drug monitoring

Conventional sampling of biological fluids often involves a bulk quantity of samples that are tedious to collect, deliver and process. Miniaturized sampling approaches have emerged as promising tools for sample collection due to numerous advantages such as minute sample size, patient friendliness and ease of shipment. This article reviews the applications and advances of microsampling techniques in therapeutic drug monitoring (TDM), covering the period January 2015 - August 2020. As whole blood is the gold standard sampling matrix for TDM, this article comprehensively highlights the most historical microsampling technique, the dried blood spot (DBS), and its development. Advanced developments of DBS, ranging from various automation DBS, paper spray mass spectrometry (PS-MS), 3D dried blood spheroids and volumetric absorptive paper disc (VAPD) and mini-disc (VAPDmini) are discussed. The volumetric absorptive microsampling (VAMS) approach, which overcomes the hematocrit effect associated with the DBS sample, has been employed in recent TDM. The sample collection and sample preparation details in DBS and VAMS are outlined and summarized. This review also delineates the involvement of other biological fluids (plasma, urine, breast milk and saliva) and their miniaturized dried matrix forms in TDM. Specific features and challenges of each microsampling technique are identified and comparison studies are reviewed.

LC-MS/MS method for nine different antibiotics

BACKGROUND AND AIMS

TDM of antibiotics can bring benefits to patients and healthcare systems by providing better treatment and saving healthcare resources. We aimed to develop a multi-analyte method for several diverse antibiotics using LC-MS/MS.

MATERIALS AND METHODS

Sample preparation consisted of protein precipitation with methanol, dilution and online extraction using a Turboflow Cyclone column. Separation was performed on a Synergi 4 µm Max RP column and deuterated forms of three antibiotics were used as internal standards.

RESULTS

We present a LC-MS/MS method for the quantitative determination of nine antibiotics, including five cephalosporins, the carbapenem ertapenem, the fluoroquinolone ciprofloxacin as well as the combination drug trimethoprim-sulfamethoxazole from plasma. Additionally, unbound ertapenem and cefazolin were analyzed in plasma water after ultrafiltration using plasma calibrators. Results from routine TDM show the applicability of the method.

CONCLUSION

The presented method is precise and accurate and was introduced in a university hospital, permitting fast TDM of all nine analytes. It was also used in a clinical study for measuring cefazolin free and total concentrations.

Physiologically Based Pharmacokinetic Modeling for Trimethoprim and Sulfamethoxazole in Children

OBJECTIVE

The aims of this study were to (1) determine whether opportunistically collected data can be used to develop physiologically based pharmacokinetic (PBPK) models in pediatric patients; and (2) characterize age-related maturational changes in drug disposition for the renally eliminated and hepatically metabolized antibiotic trimethoprim (TMP)-sulfamethoxazole (SMX).

METHODS

We developed separate population PBPK models for TMP and SMX in children after oral administration of the combined TMP-SMX product and used sparse and opportunistically collected plasma concentration samples to validate our pediatric model. We evaluated predictability of the pediatric PBPK model based on the number of observed pediatric data out of the 90% prediction interval. We performed dosing simulations to target organ and tissue (skin) concentrations greater than the methicillin-resistant Staphylococcus aureus (MRSA) minimum inhibitory concentration (TMP 2 mg/L; SMX 9.5 mg/L) for at least 50% of the dosing interval.

RESULTS

We found 67-87% and 71-91% of the observed data for TMP and SMX, respectively, were captured within the 90% prediction interval across five age groups, suggesting adequate fit of our model. Our model-rederived optimal dosing of TMP at the target tissue was in the range of recommended dosing for TMP-SMX in children in all age groups by current guidelines for the treatment of MRSA.

CONCLUSION

We successfully developed a pediatric PBPK model of the combination antibiotic TMP-SMX using sparse and opportunistic pediatric pharmacokinetic samples. This novel and efficient approach has the potential to expand the use of PBPK modeling in pediatric drug development.

Application of Rank Annihilation Factor Analysis for Antibacterial Drugs Determination by Means of pH Gradual Change-UV Spectral Data

The main objective of this study was to develop a simple and efficient spectrophotometric technique combined with chemometrics for the simultaneous determination of sulfamethoxazole (SMX) and trimethoprim (TMP) in drug formulations. Specifically, we sought: (i) to evaluate the potential use of rank annihilation factor analysis (RAFA) to pH gradual change spectrophotometric data in order to provide sufficient accuracy and model robustness; and (ii) to determine SMX and TMP concentration in drug formulations without tedious pre-treatments such as derivatization or extraction techniques which are time-consuming and require hazardous solvents. In the proposed method, the spectra of the sample solutions at different pH values were recorded and the pH-spectra bilinear data matrix was generated. On these data, RAFA was then applied to estimate the concentrations of SMX and TMP in synthetic and real samples. Applying RAFA showed that the two drugs could be determined simultaneously with concentration ratios of SMX to TMP varying from 1:30 to 30:1 in the mixed samples (concentration range is 1-30 µg mL^-1 for both components). The limits of detection were 0.25 and 0.38 µg mL^-1 for SMX and TMP, respectively. The proposed method was successfully applied to the simultaneous determination of SMX and TMP in some synthetic, pharmaceutical formulation and biological fluid samples. In addition, the means of the estimated RSD (%) were 1.71 and 2.18 for SMX and TMP, respectively, in synthetic mixtures. The accuracy of the proposed method was confirmed by spiked recovery test on biological samples with satisfactory results (90.50-109.80%).

Automated analysis of dried urine spot (DUS) samples for toxicology screening

BACKGROUND

Dried specimens have been proposed in multiple environments to minimize costs associated with specimen storage and shipping in clinical studies. This report describes the development and validation of an automated method for qualitative toxicology screening of dried urine samples using LC-MS/MS.

METHODS

Urine standards containing 41 compounds were prepared and applied to filter paper cards. Dried urine was eluted from the cards using a Dried Blood Spot (DBS) autosampler from Spark Holland, which was plumbed inline with a Thermo Scientific Turboflow chromatography system for subsequent MS/MS detection with selected reaction monitoring. Limits of detection, precision of peak areas, repeatability, and carryover studies were conducted. Concordance with a reference LC-MS/MS method using liquid samples was evaluated using remnant discarded specimens.

RESULTS

The limit of detection ranged from 5 to 75 ng/mL for most compounds. At the LOD for each analyte, the peak area precision ranged from 8 to 29%. For 20 repeat injections of samples spiked at ±25% of the LOD, there was a 4% false positive rate for the 75% × LOD samples, and a 0.4% false negative rate for the +125% × LOD samples. In comparing 40 known positive specimens analyzed with the DUS method and a liquid urine reference method, there was 88% agreement. Analysis of 10 known negative specimens yielded negative results. There was no significant carryover detected up to 2000 ng/mL for any of the analytes in the assay.

CONCLUSION

Using a robotic DUS sampling an inline HTLC-MS/MS system, we have developed and validated a fully-automated and robust method for multi-analyte detection of drugs of abuse in dried urine specimens.

Simultaneous Determination of Selegiline, Desmethylselegiline, R/S-methamphetamine, and R/S-amphetamine on Dried Urine Spots by LC/MS/MS: Application to a Pharmacokinetic Study in Urine

Objective: Chiral analysis is a crucial method to differentiate selegiline intake from drug abuse. A dried urine spot (DUS) analytical method based on spotting urine samples (10 μL) onto dried spot collection cards, and followed by air-drying and extraction, was developed and validated for the determination of selegiline, desmethylselegiline, R/S-methamphetamine, and R/S-amphetamine. Methods: Methanol (0.5 mL) was found to be the ideal extraction solvent for target extraction from DUSs under orbital-horizontal stirring on a lateral shaker at 1,450 rpm for 30 min. Determinations were performed by direct electrospray ionization tandem mass spectrometry (ESI-MS/MS) under positive electrospray ionization conditions using multiple reaction monitoring mode. The chromatographic system consisted of a ChirobioticTM V2 column (2.1 × 250 mm, 5 μm) and a mobile phase of methanol containing 0.1% (v/v) glacial acetic acid and 0.02% (v/v) ammonium hydroxide. Results and conclusions: The calibration curves were linear from 50 to 5,000 ng/mL, with r > 0.995 for all analytes, imprecisions ≤ 15% and accuracies between -11.4 and 11.7%. Extraction recoveries ranged from 48.6 to 105.4% with coefficients of variation (CV) ≤ 13.7%, and matrix effects ranged from 45.4 to 104.1% with CV ≤ 10.3%. The lower limit of quantification was 50 ng/mL for each analyte. The present method is simple, rapid (accomplished in 12 min), sensitive, and validated by a pharmacokinetic study in human urine collected after a single oral administration of SG.

Innovative Study Designs Optimizing Clinical Pharmacology Research in Infants and Children

Almost half of recent pediatric trials failed to achieve labeling indications, in large part because of inadequate study design. Therefore, innovative study methods are crucial to optimizing trial design while also reducing the potential harms inherent with drug investigation. Several methods exist to optimize the amount of pharmacokinetic data collected from the smallest possible volume and with the fewest number of procedures, including the use of opportunistic and sparse sampling, alternative and noninvasive matrices, and microvolume assays. In addition, large research networks using master protocols promote collaboration, reduce regulatory burden, and increase trial efficiency for both early- and late-phase trials. Large pragmatic trials that leverage electronic health records can capitalize on central management strategies to reduce costs, enroll patients with rare diseases on a large scale, and augment study generalizability. Further, trial efficiency and safety can be optimized through Bayesian adaptive techniques that permit planned protocol changes based on analyses of prior and accumulated data. In addition to these trial design features, advances in modeling and simulation have paved the way for systems-based and physiologically based models that individualize pediatric dosing recommendations and support drug approval. Last, given the low prevalence of many pediatric diseases, collecting deidentified genetic and clinical data on a large scale is a potentially transformative way to augment clinical pharmacology research in children.

Dried urine swabs as a tool for monitoring metabolite excretion

Aim: We tested a large set (n = 181) of wet urine and dried urine samples spotted on regular cosmetic cotton swabs for comparative UHPLC–MS/MS analysis of various metabolites across a wide polarity and structural range. Results/methodology: The agreement of measurements between conventional 24 h urines and dried urine spots made from them in situ was evaluated by Passing–Bablok regression and Bland–Altman analysis after creatinine correction. There was full agreement in qualitative results but quantitative analysis revealed underestimation of dried urine spots in some cases. The dried urine samples contained analytes at measurable levels for at least 9 months. Conclusion: Although this technique seems very promising more methodological studies have to be conducted in order to improve applicability of dried urine microvolume fluidic sampling for quantitative analysis.

Population Pharmacokinetics of Intramuscular and Intravenous Ketamine in Children

Ketamine is an N-methyl D-aspartate receptor antagonist used off-label to facilitate dissociative anesthesia in children undergoing invasive procedures. Available for both intravenous and intramuscular administration, ketamine is commonly used when vascular access is limited. Pharmacokinetic (PK) data in children are sparse, and the bioavailability of intramuscular ketamine in children is unknown. We performed 2 prospective PK studies of ketamine in children receiving either intramuscular or intravenous ketamine and combined the data to develop a pediatric population PK model using nonlinear mixed-effects methods. We applied our model by performing dosing simulations targeting plasma concentrations previously associated with analgesia (>100 ng/mL) and anesthesia awakening (750 ng/mL). A total of 113 children (50 intramuscular and 63 intravenous ketamine) with a median age of 3.3 years (range 0.02 to 17.6 years), and median weight of 14 kg (2.4 to 176.1) contributed 275 plasma samples (149 after intramuscular, 126 after intravenous ketamine). A 2-compartment model with first-order absorption following intramuscular administration and first-order elimination described the data best. Allometrically scaled weight was included in the base model for central and peripheral volume of distribution (exponent 1) and for clearance and intercompartmental clearance (exponent 0.75). Model-estimated bioavailability of intramuscular ketamine was 41%. Dosing simulations suggest that doses of 2 mg/kg intravenously and 8 mg/kg or 6 mg/kg intramuscularly, depending on age, provide adequate sedation (plasma ketamine concentrations >750 ng/mL) for procedures lasting up to 20 minutes.

Clinical application of microsampling versus conventional sampling techniques in the quantitative bioanalysis of antibiotics: a systematic review

Conventional sampling techniques for clinical pharmacokinetic studies often require the removal of large blood volumes from patients. This can result in a physiological or emotional burden, particularly for neonates or pediatric patients. Antibiotic pharmacokinetic studies are typically performed on healthy adults or general ward patients. These may not account for alterations to a patient’s pathophysiology and can lead to suboptimal treatment. Microsampling offers an important opportunity for clinical pharmacokinetic studies in vulnerable patient populations, where smaller sample volumes can be collected. This systematic review provides a description of currently available microsampling techniques and an overview of studies reporting the quantitation and validation of antibiotics using microsampling. A comparison of microsampling to conventional sampling in clinical studies is included.

Population Pharmacokinetics of Trimethoprim-Sulfamethoxazole in Infants and Children

Trimethoprim (TMP)-sulfamethoxazole (SMX) is used to treat various types of infections, including community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) and Pneumocystis jirovecii infections in children. Pharmacokinetic (PK) data for infants and children are limited, and the optimal dosing is not known. We performed a multicenter, prospective PK study of TMP-SMX in infants and children. Separate population PK models were developed for TMP and SMX administered by the enteral route using nonlinear mixed-effects modeling. Optimal dosing was determined on the basis of the matching adult TMP exposure and attainment of the surrogate pharmacodynamic (PD) target for efficacy, a free TMP concentration above the MIC over 50% of the dosing interval. Data for a total of 153 subjects (240 samples for PK analysis) with a median postnatal age of 8 years (range, 0.1 to 20 years) contributed to the analysis for both drugs. A one-compartment model with first-order absorption and elimination characterized the TMP and SMX PK data well. Weight was included in the base model for clearance (CL/F) and volume of distribution (V/F). Both TMP and SMX CL/F increased with age. In addition, TMP and SMX CL/F were inversely related to the serum creatinine and albumin concentrations, respectively. The exposure achieved in children after oral administration of TMP-SMX at 8/40 mg/kg of body weight/day divided into administration every 12 h matched the exposure achieved in adults after administration of TMP-SMX at 320/1,600 mg/day divided into administration every 12 h and achieved the PD target for bacteria with an MIC of 0.5 mg/liter in >90% of infants and children. The exposure achieved in children after oral administration of TMP-SMX at 12/60 and 15/75 mg/kg/day divided into administration every 12 h matched the exposure achieved in adults after administration of TMP-SMX at 640/3,200 mg/day divided into administration every 12 h in subjects 6 to <21 years and 0 to <6 years of age, respectively, and was optimal for bacteria with an MIC of up to 1 mg/liter.

UPLC-MS/MS method for therapeutic drug monitoring of 10 antibiotics used in intensive care units

A large variation in the levels of different ß-lactams and other antibiotics used in critically ill patients has been documented. The aim of this study is to establish and validate a fast, ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for the simultaneous analysis of ten antibiotics (Meropenem, Cefepime, Ceftazidime, Piperacillin, Benzylpenicillin, Ampicillin, Flucloxacillin, Linezolid, and Sulfamethoxazole/Trimethoprim) in human plasma according to European Medicines Agency (EMA) guidelines. Protein precipitation with ice-cold methanol containing 9 isotopically labeled internal standards was used for sample clean up. Antibiotics were detected, following a 4-minute gradient separation, in multiple reactions monitoring (MRM) using API 4000 instrument equipped with electrospray source operating in positive ion mode. The lower limit of quantification was 0.1 mg/L for Meropenem, Ceftazidime, Piperacillin, Ampicillin, Flucloxacillin, and Sulfamethoxazole; 0.05 mg/L for Cefepime, Benzylpenicillin, and Trimethoprim; and 0.02 mg/L for Linezolid. The method proved to be precise and accurate and applicable for therapeutic drug monitoring and other pharmacokinetic studies.

Quantification of Warfarin in Dried Rat Plasma Spots by High-Performance Liquid Chromatography with Tandem Mass Spectrometry

This paper presents the development and validation of a novel method for quantification of the oral anticoagulant drug warfarin in dried plasma spots (DPS) by high-performance liquid chromatography with tandem mass spectrometry (HPLC-MS/MS). Blood plasma was chosen as a biological fluid to preclude the influence of the hematocrit on the results of the analysis. A 30 μL sample of rat plasma was placed onto Whatman 903 Protein Saver Card and was allowed to dry. A single DPS is sufficient for preparing eight 3.2 mm discs, each containing approximately 1.5-1.6 μL of plasma. Warfarin extraction from one 3.2 mm disc was carried out by adding 200 μL of the acetonitrile : water mixture (1 : 1, v/v) containing 10 mM NH₄COOH (pH 4.0), with incubation on a shaker at 1000 rpm for 1 h at 25°C. After chromatographic separation, warfarin and coumachlor (an internal standard) were measured using negative-ion multiple-reaction monitoring with ion transitions m/z 307 → 161 for warfarin and m/z 341 → 161 for the internal standard. The working range of this method is 10-10,000 ng/mL. Within this range, intra- and interday variability of precision and accuracy was <13% and recovery was 82-99%. The results indicate that the new method requires only small plasma samples and may be useful for pharmacokinetic research on warfarin.

Uncertainty in Antibiotic Dosing in Critically Ill Neonate and Pediatric Patients: Can Microsampling Provide the Answers?

PURPOSE

With a decreasing supply of antibiotics that are effective against the pathogens that cause sepsis, it is critical that we learn to use currently available antibiotics optimally. Pharmacokinetic studies provide an evidence base from which we can optimize antibiotic dosing. However, these studies are challenging in critically ill neonate and pediatric patients due to the small blood volumes and associated risks and burden to the patient from taking blood. We investigate whether microsampling, that is, obtaining a biologic sample of low volume (<50 μL), can improve opportunities to conduct pharmacokinetic studies.

METHODS

We performed a literature search to find relevant articles using the following search terms: sepsis, critically ill, severe infection, intensive care AND antibiotic, pharmacokinetic, p(a)ediatric, neonate. For microsampling, we performed a search using antibiotics AND dried blood spots OR dried plasma spots OR volumetric absorptive microsampling OR solid-phase microextraction OR capillary microsampling OR microsampling. Databases searched include Web of Knowledge, PubMed, and EMbase.

FINDINGS

Of the 32 antibiotic pharmacokinetic studies performed on critically ill neonate or pediatric patients in this review, most of the authors identified changes to the pharmacokinetic properties in their patient group and recommended either further investigations into this patient population or therapeutic drug monitoring to ensure antibiotic doses are suitable. There remain considerable gaps in knowledge regarding the pharmacokinetic properties of antibiotics in critically ill pediatric patients. Implementing microsampling in an antibiotic pharmacokinetic study is contingent on the properties of the antibiotic, the pathophysiology of the patient (and how this can affect the microsample), and the location of the patient. A validation of the sampling technique is required before implementation.

IMPLICATIONS

Current antibiotic regimens for critically ill neonate and pediatric patients are frequently suboptimal due to a poor understanding of altered pharmacokinetic properties. An assessment of the suitability of microsampling for pharmacokinetic studies in neonate and pediatric patients is recommended before wider use. The method of sampling, as well as the method of bioanalysis, also requires validation to ensure the data obtained reflect the true result.

Solithromycin Pharmacokinetics in Plasma and Dried Blood Spots and Safety in Adolescents

We assessed the pharmacokinetics and safety of solithromycin, a fluoroketolide antibiotic, in a phase 1, open-label, multicenter study of 13 adolescents with suspected or confirmed bacterial infections. On days 3 to 5, the mean (standard deviation) maximum plasma concentration and area under the concentration versus time curve from 0 to 24 h were 0.74 μg/ml (0.61 μg/ml) and 9.28 μg · h/ml (6.30 μg · h/ml), respectively. The exposure and safety in this small cohort of adolescents were comparable to those for adults. (This study has been registered at ClinicalTrials.gov under registration no. NCT01966055.).

Challenges facing effective implementation of co-trimoxazole prophylaxis in children born to HIV-infected mothers in the public health facilities

BACKGROUND

If children born to HIV-infected mothers are not identified early, approximately 30% of them will die within the first year of life due to opportunistic infections. In order to prevent morbidity and mortality due to opportunistic infections in children, the World Health Organization recommends the use of prophylaxis using co-trimoxazole. However, the challenges affecting effective implementation of this policy in Tanzania have not been documented.

AIM

In this study, we assessed the challenges facing the provision of co-trimoxazole prophylaxis among children born to HIV-infected mothers in the public hospitals of Dar es Salaam, Tanzania.

METHODOLOGY

Four hundred and ninety-eight infants' PMTCT (Prevention of Mother-to-Child Transmission of HIV) register books for the past 2 years were reviewed to obtain information regarding the provision of co-trimoxazole prophylaxis. One hundred and twenty-six health care workers were interviewed to identify success stories and challenges in the provision of co-trimoxazole prophylaxis in children. In addition, 321 parents and guardians of children born to HIV-infected mothers were interviewed in the health facilities.

RESULTS

Approximately 80% of children were initiated with co-trimoxazole prophylaxis within 2 months after birth. Two hundred and ninety-one (58.4%) children started using co-trimoxazole within 4 weeks after birth. Majority (n=458, 91.8%) of the children were prescribed 120 mg of co-trimoxazole per day, whereas 39 (7.8%) received 240 mg per day. Only a small proportion (n=1, 0.2%) of children received 480 mg/day. Dose determination was based on the child's age rather than body weight. Parents and guardians reported that 42 (13.1%) children had missed one or more doses of co-trimoxazole during the course of prophylaxis. The majority of health care workers (89.7%) reported that co-trimoxazole is very effective for the prevention of opportunistic infections among children, but frequent shortage of co-trimoxazole in the health facilities was the main challenge.

CONCLUSION

Most children who were initiated with co-trimoxazole prophylaxis did not experience significant opportunistic infections, and the drug was well tolerated. The major barrier for co-trimoxazole prophylaxis was due to frequent out-of-stocks of pediatric co-trimoxazole formulations in the health facilities. Dose determination was based on the age rather than the weight of children, thus creating potential for under- or over-dosing of children.