Volumetric absorptive microsampling (VAMS) is a novel approach to obtaining a dried blood sample for quantitative bioanalysis that overcomes the area bias and homogeneity issues associated with conventional dried blood spot (DBS) sample when a subpunch is taken. The VAMS sampler absorbs a fixed volume of blood (∼10 μL) in 2–4 s with less than 5% volume variation across the hematocrit range of 20–70% with low tip-to-tip variability. There is no evidence of selective absorption by the tip of the plasma component over whole blood. Recommendations for best practice when collecting samples were developed based upon the results of tests examining a number of potential abuse scenarios.

Volumetric absorptive microsampling: a dried sample collection technique for quantitative bioanalysis.

This article discusses dried blood spot (DBS) sampling in therapeutic drug monitoring (TDM). The most important advantages of DBS sampling in TDM are the minimally invasive procedure of a finger prick (home sampling), the small volume (children), and the stability of the analyte. Many assays in DBS have been reported in the literature over the previous 5 years. These assays and their analytical techniques are reviewed here. Factors that may influence the accuracy and reproducibility of DBS methods are also discussed. Important issues are the correlation with plasma/serum concentrations and the influence of hematocrit on spot size and recovery. The different substrate materials are considered. DBS sampling can be a valid alternative to conventional venous sampling. However, patient correlation studies are indispensable to prove this. Promising developments are dried plasma spots using membrane and hematocrit correction using the potassium concentration.

https://link.springer.com/content/pdf/10.1007%2Fs40262-014-0177-7.pdf

Therapeutic Drug Monitoring by Dried Blood Spot: Progress to Date and Future Directions

Because of the low concentration levels in plasma, blood, urine, and other metabolites, adequate analytical methods should be used for quantification of drugs at the trace levels. Molecularly imprinted polymers (MIPs) are tailor made and stable polymers with special molecular recognition abilities that because of their high selectivity can be used for the extraction of selected target analytes and structurally related analogues in many bioanalytical approaches. Nowadays, MIPs are rapidly progressing for the analysis of drugs in biological, environmental, and pharmaceutical samples. In this review, we discuss the novel developments and uses of MIPs as new sorbents and fibers in solid phase extraction (SPE) and solid phase microextraction (SPME), ultrasonic-assisted SPE, sensitive sensors, magnetic separations or conjugating with carbon materials for trace and ultra-trace determination of drugs. We believe that our review will be of assistance to drug analysis and analytical methods with highly selective separations/detections.

Novel developments and trends of analytical methods for drug analysis in biological and environmental samples by molecularly imprinted polymers

Introduction Through the introduction of advanced analytical techniques and improved throughput, the scope of dried blood spot testing utilising mass spectrometric methods, has broadly expanded. Clinicians and researchers have become very enthusiastic about the potential applications of dried blood spot based mass spectrometric applications. Analysts on the other hand face challenges of sensitivity, reproducibility and overall accuracy of dried blood spot quantification. In this review, we aim to bring together these two facets to discuss the advantages and current challenges of non-newborn screening applications of dried blood spot quantification by mass spectrometry. Methods To address these aims we performed a key word search of the PubMed and MEDLINE online databases in conjunction with individual manual searches to gather information. Keywords for the initial search included; "blood spot" and "mass spectrometry"; while excluding "newborn"; and "neonate". In addition, databases were restricted to English language and human specific. There was no time period limit applied. Results As a result of these selection criteria, 194 references were identified for review. For presentation, this information is divided into: 1) clinical applications; and 2) analytical considerations across the total testing process; being pre-analytical, analytical and post-analytical considerations. Conclusions DBS analysis using MS applications is now broadly applied, with drug monitoring for both therapeutic and toxicological analysis being the most extensively reported. Several parameters can affect the accuracy of DBS measurement and further bridge experiments are required to develop adjustment rules for comparability between dried blood spot measures and the equivalent serum/plasma values. Likewise, the establishment of independent reference intervals for dried blood spot sample matrix is required.

Advantages and Challenges of Dried Blood Spot Analysis by Mass Spectrometry Across the Total Testing Process.

Dried blood spots analysis with mass spectrometry: Potentials and pitfalls in therapeutic drug monitoring

A simple dried blood spot method for therapeutic drug monitoring of the tricyclic antidepressants amitriptyline, nortriptyline, imipramine, clomipramine, and their active metabolites using LC-MS/MS.

Dried blood spot (DBS) sampling and quantitative analyses of many current therapeutic drug monitoring (TDM)-guided drugs are advantageous because of the minimal invasive sampling strategy. Here, a fast and robust LC-MS/MS method was developed and analytically validated for simultaneous determination of venlafaxine (VEN) and O-desmethylvenlafaxine (ODV) in DBS. Six-millimeter circles were punched out from DBS collected on Whatman DMPK-C paper, and the DBS was extracted with acetonitrile/methanol at 1:3. The total run time was 4.8 min. The assay was linear in the range of 20–1,000 μg/L for both VEN and ODV. Assay accuracy and precision was well within limits of acceptance (LLOQ = 20 μg/L). Normal hematocrit concentrations (0.30–0.50) did not influence the results neither did a normal spot volume (40–80 μL). Punch position at the perimeter instead of the center of the blood spot gave a bias ranging from 2.4 to 10.4 %. Correlation between plasma and spiked DBS samples was high. The concentrations found in spiked DBS samples were higher than those in plasma, indicating that a conversion factor for translation of DBS to plasma values is needed. This analytically validated method is suitable for determination of VEN and ODV in DBS and applicable for TDM. The method will be used for TDM of VEN in the Dutch CYSCE multicenter trial (NCT01778907).

Determination of venlafaxine and O-desmethylvenlafaxine in dried blood spots for TDM purposes, using LC-MS/MS.

Background: Venlafaxine (VEN) is an antidepressant which exerts both serotonin and norepinephrine reuptake inhibition. The drug is mainly metabolized by CYP2D6 to its active metabolite O-desmetylvenlafaxine (ODMV). Due to large interindividual differences in clearance in which genetic variance in CYP2D6 activity plays a major role, therapeutic drug monitoring (TDM) is considered useful in patients treated with VEN. We developed an assay for combined determination of VEN and ODMV in dried blood spots (DBS). Methods: A fast and robust LC-MS/MS method was developed and fully validated for simultaneous determination of VEN and ODMV in DBS. 9 mm circles were punched out from DBS collected on Whatman DMPK-C paper and mixed with acetonitril:methanol 1:3 containing the internal standard. The extract was analyzed by LC-MS/MS. Results: The assay was found to be linear in the range 20-1000 mcg/L for both VEN and ODMV. Inter-assay variability at LLQ (20 mcg/L), Low (L, 80 mcg/L), Medium (M, 300 mcg/L) and High (H, 750 mcg/L) levels was 12.0%, 6.1%, 7.0%, and 4.9% for VEN and 10.8%, 6.8%, 5.4%, and 6.3% respectively for ODMV. Bias at LLQ, L, M and H was 7.2%, 1.3%, 0.2%, and 20.4% for VEN and 5.6%, 1.7%, 0.4%, and 0% for ODMV. The influence of punch position and blood volume per spot did not influence the results, but a low hematocrit (10% negative bias. Comparison of venous blood samples with DBS samples revealed a linear correlation with a R2 of >0.98 and a DBS/plasma ratio of 1.11 for VEN and 1.28 for ODMV. Conclusions: This fully validated method is suitable for determination of VEN and its metabolite ODMV in DBS and applicable for TDM. The method will be used in the Dutch CYSCE multicenter trial (ClincialTrail.gov Identifier NCT01778907) in which the effect of CYP2D6 genotyping combined with TDM on time to reach adequate blood drug levels will be investigated in depressed elderly patients.

J. Paardekooper

Papers

A simple dried blood spot method for therapeutic drug monitoring of the tricyclic antidepressants amitriptyline, nortriptyline, imipramine, clomipramine, and their active metabolites using LC-MS/MS.

Determination of venlafaxine and O-desmethylvenlafaxine in dried blood spots for TDM purposes, using LC-MS/MS.

Determination of venlafaxine and O-desmethylvenlafaxine in dried blood spots using LC-MS/MS