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microsampling for TDM of antidepressants in neurodegenerative diseases

by James Rudge, PhD, Technical Director, Neoteryx | 5 min read

An article by Laura Mercolini et al at the University of Bologna published in the August 2020 issue of Analyst, reported on a thorough validation of the suitability the hemaPEN® microsampling device for two serotonin reuptake inhibitors intended for therapeutic drug monitoring (TDM) applications. The paper is entitled “Assessment of capillary volumetric blood microsampling for the analysis of central nervous system drugs and metabolites.” It describes the development and validation of fluoxetine, norfluoxetine, sertraline and N-desmethylsertraline from dried blood extracted from DBS samples collected volumetrically using hemaPEN.

image-1-1The research group was able to fully validate the assay and reported that the original capillary volumetric microsampling procedure using hemaPEN was suitable for the accurate sampling of capillary whole blood. The group proposed that the method could be successfully exploited in self-collection and home-sampling procedures in future and to “pave the way for precision medicine approaches for the treatment of CNS disorders.”

The Burden & Impact of Neurodegenerative Diseases

Being diagnosed with an incurable neurodegenerative disease is devastating for those affected and those close to them. The strain it causes can lead to severe anxiety and depression. Treatments given to CNS patients often have limited effect and may only treat symptoms. Other treatments may only slow down the progression of the disease. For example, the drug riluzole is one of the only treatments shown to extend life, to a limited degree, in patients with amyotrophic lateral sclerosis (otherwise known as motor neurons disease). If CNS conditions often occur later in life, older patients may already be taking a cocktail of drugs to treat other conditions, such as hypertension, high cholesterol and diabetes. Adding CNS-related medications to an already rigorous medication schedule can cause challenges or complications.Anitdepressants-iStock-1218204713Treatment approaches for neurodegenerative diseases typically take a two-pronged approach. Care providers treat the physical effects of the neurodegenerative disease with drug therapies, while also prescribing therapies that treat anxiety and depression for those who are affected. Antidepressants have been shown to be effective for treating depression in those suffering from central nervous system (CNS) disorders. For a number of reasons, therapeutic drug monitoring (TDM) of people who are taking antidepressants is advised, especially for patients who are taking a range of other medications - including those taking drugs active on the central nervous system.

One such class of antidepressants are the second-generation antidepressants called serotonin reuptake inhibiters (SSRIs). The safety profiles of SSRIs are considered to be more favorable than many first-generation drugs, such as tricyclic antidepressants. SSRIs act by increasing levels of the neurotransmitter serotonin in the brain. Serotonin is associated with increased sense of wellbeing, increased appetite, and regulation of the body clock.

Where does microsampling fit in?

Use of dried matrix remote specimen collection and microsampling, whereby patient-collected specimens can be mailed to a central lab for analysis, helps care teams to more conveniently monitor drug levels in people. Remote microsampling has potential benefits for patients with CNS disorders. One such benefit is that as a CNS disease progresses, mobility and/or cognition become progressively hindered. As a result, clinic visits for onsite bloodwork and health checks become more challenging. With remote microsampling, people can collect their specimen samples in the comfort of their own homes and mail them in. This home sampling approach could be a game-changer for CNS patients and their carers.

To explore the possibilities, the team led by Laura Mercolini investigated the use of the hemaPEN as a potential remote microsampling device for monitoring two SSRIs and metabolites. The hemaPEN is an ideal patient-centric sampling tool for remote TDM. It simultaneously collects four capillary samples from a single source – a finger-prick, for example. After sampling, the end-user places the hemaPEN onto its plastic base and “clicks” it shut. This action transfers the four capillary samples onto 4 pre-cut DBS disks inside the hemaPEN, delivering four homogenous DBS samples secured in the device’s tamper-resistant housing that includes desiccant.

This device is easy to use by most patients, because hemaPEN sampling can be achieved at any angle without the fear of oversampling. In the lab, the internal DBS disks are removed from the device using a special opening tool. and the DBS samples are then extracted by pushing the disks from their cartridge into extractant in a workflow reminiscent of traditional DBS. The critical difference is that the hemaPEN allows for volumetric quantitation.

CNS Study Method and Findings

  • SSRIs and metabolites studied were fluoxetine, norfluoxetine, sertraline and N-desmethylsertraline.

  • Whole blood capillary samples were collected from healthy volunteers and venous blood samples were obtained from patients for method application.

  • Spiked venous blood was used for method validation. Both dried whole blood from hemaPEN collection and wet plasma were compared.

  • Method validation was conducted following European Medicines Agency (EMA) and US Food and Drug Administration (FDA) guidelines on bioanalytical method validation but also taking DBS-specific parameters into account.

  • The hemaPEN samples (n=6, 2.74 µL) were shown to collect blood at high levels of accuracy (102%) and precision (1.9% RSD).

  • Extraction optimization was carried out and 50 µL of MeOH sonicating for 30 minutes and the supernatant was then centrifuged and injected onto the LC-MS/MS system for quantitation.

  • Excellent linearity was seen for all target compounds r2 ≥ 0.9991 across 3 orders of magnitude.

  • Extraction yields were > 81% for all analytes and precision was well within accepted criteria as well as acceptable carryover.

  • Matrix effects were all below 8% and all compounds at low-high QC levels were well within ± 15% acceptance criteria across a hematocrit (HCT) range (30, 50 and 70% HCT).

  • Stability was shown to be excellent for all compounds with less than 5.2% loss for five days at 50° C and 6.3% at room temperature for at least 3 months.

  • Under- and over-sampling were evaluated by sampling blood at different durations (10 seconds is recommended in the IFU). No over-sampling was observed even at 20 seconds sample time. The minimum time where all 4 spots were sampled was 8 seconds.
    • At 6 seconds, 2 complete spots were sampled leaving 2 blanks
    • At 4 seconds this was down to 1 completed spot plus 3 blanks
    • At 2 seconds, all blanks
Comparing whole dried blood extracts to standard paired wet plasma and correcting for pre-determined erythrocyte-to-plasma concentration ratios, the whole dataset showed a strong correlation (r2 = ≥0.9896) and a negligible mean bias from the Bland–Altman data.

Study Authors’ Conclusions

The fully validated method from hemaPEN extracts, provided reliable and sound analytical results and allowed for assessment of the potential application of sampling patients on CNS disorder patients on antidepressants. The high throughput method was straightforward to allow for reliable TDM of such patients. The sampling accuracy and robustness showed promising results, “remarkable” analyte stability, and “outstanding” HCT-independence. The hemaPEN tool has high potential for a home sampling approach to therapeutic drug monitoring to allow for more frequent sampling that would allow better clinical decision making and therapy personalization.

Neoteryx Comments

The authors should be commended on such a thorough analytical validation and device evaluation. The importance of providing patients with an option for self- or assisted sampling cannot be underestimated, especially for those who are debilitated with disorders that cause loss of mobility and/or cognition. Volumetric dried blood microsampling, whatever the chosen tool, really demonstrates the feasibility of how care can be continued remotely to allow those affected to minimize unnecessary travel to clinics and experience less invasive blood sampling. Moreover, remote devices offer the potential for more frequent sampling to further tailor treatment for those affected by devastating disorders.

This article was summarized for our readers by James Rudge, PhD, Neoteryx Technical Director. This is curated content. To learn more about the important research outlined in this blog, visit the original article in Analyst.

Image Credits: iStock, Neoteryx, Trajan Scientific and Medical

You can access this microsampling article and others in our Technical Resource Library.

Online Library copy

 

Originally published Aug 1, 2022 9:00:00 AM, updated on August 1, 2022

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