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.

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.

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.

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.

Expanding the knowledge on dried blood spots and LC-MS-based protein analysis: two different sampling materials and six protein targets

The combination of dried blood spots (DBS) and bottom-up LC-MS-based protein analysis was investigated in the present paper using six model proteins (1 mg/mL of each protein) with different physicochemical properties. Two different materials for DBS were examined: a water-soluble DBS material (carboxymethyl cellulose, (CMC)) and a commercially available (non-soluble) material (DMPK-C). The sample preparation was optimised regarding the water-soluble material and achieving acceptable repeatability of the signal was emphasised. Five microlitres of whole blood were deposited and dried on either CMC or DMPK-C. The samples were dissolved (CMC) or extracted (DMPK-C) prior to tryptic digest and matrix precipitation. The optimization of the sample preparation showed that an increased buffer concentration (100 mM ammonium bicarbonate) for dissolving the DBS samples gave better repeatability combined with a decrease in analyte signal. CMC seemed to add extra variability (RSD 8-60%) into the analysis compared to sample prepared without CMC (RSD 6-36%), although equal performance compared to DMPK-C material (RSD 13-60%) was demonstrated. The stability of the analytes was examined for different storage periods (1 and 4 weeks) and different storage temperatures (-25, 25, and 40 °C). The stability on both CMC (> 70% compared to reference) and DMPK-C (> 50% compared to reference) was acceptable for most of the peptides. This paper shows that both DBS materials can be used in targeted LC-MS-based protein analysis of proteins with different physicochemical properties. Graphical Abstract Overview of the experimental set-up for expanding the knowledge of dried blood spots in LC-MS-based protein anaysis.

Low-voltage electrochemically stimulated stir membrane liquid-liquid microextraction as a novel technique for the determination of methadone

In the present work, for the first time, a new portable setup was designed, developed and presented for the extraction of methadone, as a basic drug model from biological fluid samples using a low-voltage electrically stimulated stir membrane liquid-liquid microextraction technique (LV-ESSM-LLME), followed by high-performance liquid chromatography with ultraviolet detection. This new approach combines the advantages of stir membrane liquid-liquid microextraction and electrokinetic migration in the same unit under soft electrochemical conditions in a portable device, allowing for the isolation and preconcentration of the target analyte in a simple and efficient manner under three-phase mode. To investigate the influence of external stirring and the application of electrical potential as the driving force, a comparative study of all variables involved in the extraction process was carried out using the low-voltage electromembrane extraction (LV-EME) and LV-ESSM-LLME methods. Under soft electrokinetic migration conditions, methadone was transported from an acidic sample solution (pH 4.0), through the NPOE immobilized in the pores of the porous polypropylene sheet membrane, and into 25µL of 10mmolL^-1 HCl acceptor solution with a stirring rate of 1000rpm and 700rpm after 15min and 20min for LV-ESSM-LLME and LV-EME, respectively. Under the optimized conditions, preconcentration factors in the range of 17-24 and 21.5-29 for LV-EME and LV-ESSM-LLME, respectively, were considered, and satisfactory repeatability (4.5<[RSD]<7.5) was obtained in different matrices. The obtained relative recoveries of the target analyte were in the range of 87-94% and 93-101% for LV-EME and LV-ESSM-LLME, respectively, which indicated the excellent capability of the developed methods to extract methadone from complex matrices.

Evaluation of water-soluble DBS for small proteins: a conceptual study using insulin as a model analyte

Aim: Water-soluble sampling materials for DBS have been introduced to solve some of the common challenges of DBS. Methodology: Carboxymethyl cellulose (CMC) as water-soluble material was evaluated for small proteins using insulin as model analyte. 15 µl of whole blood was deposited and dried on a sheet of CMC prior to dissolvation of the whole spot, matrix precipitation with acetonitrile and LC–MS/MS analysis. Results: CMC was shown to promote matrix precipitation resulting in cleaner extracts than precipitation without CMC present. The recovery of insulin from the spot was 68 ± 4%, and the spotted samples were stable for at least 1 week in room temperature. Conclusion: Water-soluble DBS showed promising performance also in analysis of small proteins.

Electrically stimulated liquid-based extraction techniques in bioanalysis

Sample preparation is a vital and inseparable part of an analytical procedure. This issue has motivated the analytical research community around the world to develop new, fast and cost-effective extraction methods which can eliminate interfering substances, provide high preconcentration factors and increase the determination sensitivity. Electrical field induced extraction technique is a topic that has received major attention in recent years. This fact can be attributed to the considerable advantages provided by imposition of an electrical driving force especially control of different properties of an extraction system such as selectivity, cleanup, rate and efficiency. In this review, focus is centered on the electrical field induced liquid phase extraction techniques and their potential for bioanalysis.

Oral fluid drug analysis in the age of new psychoactive substances

Oral fluid has become an important matrix for drugs of abuse analysis. These days the applicability is challenged by the fact that an increasing number of new psychoactive drugs are coming on the market. Synthetic cannabinoids and synthetic cathinones have been the main drug classes, but the diversity is increasing and other drugs like piperazines, phenethylamines, tryptamines, designer opioids and designer benzodiazepines are becoming more prevalent. Many of the substances are very potent, and low doses ingested will lead to low concentrations in biological media, including oral fluid. This review will highlight the phenomenon of new psychoactive substances and review methods for oral fluid drug testing analysis using on-site tests, immunoassays and chromatographic methods.

Electromembrane extraction as a rapid and selective miniaturized sample preparation technique for biological fluids

This special report discusses the sample preparation method electromembrane extraction, which was introduced in 2006 as a rapid and selective miniaturized extraction method. The extraction principle is based on isolation of charged analytes extracted from an aqueous sample, across a thin film of organic solvent, and into an aqueous receiver solution. The extraction is promoted by application of an electrical field, causing electrokinetic migration of the charged analytes. The method has shown to perform excellent clean-up and selectivity from complicated aqueous matrices like biological fluids. Technical aspects of electromembrane extraction, important extraction parameters as well as a handful of examples of applications from different biological samples and bioanalytical areas are discussed in the paper.

The potential of electromembrane extraction for bioanalytical applications

Modern requirements in the field of bioanalysis often involve miniaturized, high-throughput sample preparation techniques that consume low amounts of both sample and potentially hazardous organic solvents. Electromembrane extraction is one technique that meets several of these requirements. In this principle analytes are selectively extracted from a biological matrix, through a supported liquid membrane and into an aqueous acceptor solution. The whole extraction process is facilitated by an electric field across the supported liquid membrane, which greatly reduces the extraction time. This review will give a thorough overview of recent advances in bioanalytical applications involving electromembrane extraction, and discuss both possibilities and challenges of the technique in a bioanalytical setting.

Direct drug analysis from oral fluid using medical swab touch spray mass spectrometry

Fourteen common drugs of abuse were identified in spiked oral fluid (ng mL(-1) levels), analyzed directly from medical swabs using touch spray mass spectrometry (TS-MS), exemplifying a rapid test for drug detection. Multiple stages of mass analysis (MS(2) and MS(3)) provided identification and detection limits sought by international forensic and toxicological societies, Δ(9)-THC and buprenorphine excluded. The measurements were made using a medical swab as both the sampling probe and means of ionization. The adaptation of medical swabs for TS-MS analysis allows non-invasive and direct sampling of neat oral fluid. Data acquisition was rapid, seconds per drug, and MS(3) ensured reliable identification of illicit drugs. The reported data were acquired to investigate (i) ionization of common drugs from commercial swabs, (ii) ion intensity over spray duration, and (iii) dynamic range, all as initial steps in development of a quantitative method. The approach outlined is intended for point-of-care drug testing using oral fluid in clinical applications as well as in situ settings, viz. in forensic applications. The proof-of-concept results presented will require extension to other controlled substances and refinement in analytical procedures to meet clinical/legal requirements.

Bioanalysis annual round-up: the bioanalysis editorial team is delighted to welcome you to this mid-year round-up

This year has so far proven to be another eventful one for the journal and its affiliated website Bioanalysis Zone. Key highlights include the unveiling of the finalists for the annual Young Investigator Award [1] , the publication of four exciting special issues and a selection of noteworthy White Papers, as well as the addition of more new features on Bioanalysis Zone. Not only this, but the Impact Factor of Bioanalysis increased to 3.253 (2012), demonstrating the journal's continuing high editorial standards. This mid-year round-up looks at the highlights of the year to date and features a selection of must-read articles from volume 5. Enjoy!

State-of-the-art dried blood spot analysis: an overview of recent advances and future trends

Dried blood spots have become a popular method in a variety of micro blood-sampling techniques in the life sciences sector, consequently competing with the field of conventional, invasive blood sampling by venepuncture. Dried blood spots are widely applied in numerous bioanalytical assays and have gained a significant role in the screening of inherited metabolic diseases, in PK and PD modeling; in the treatment and diagnosis of infectious diseases; and in therapeutic drug monitoring. Recent technological developments such as automation, online extraction, mass spectrometric direct analysis and also conventional dried blood spot bioanalysis, as well as future developments in dried blood spot bioanalysis are highlighted and presented in this article.