Clinical validation of a dried blood spot (DBS) method for the analysis of immunosuppressive and antifungal drugs in pediatric patients (part of the PROTECT study).

Therapeutic drug monitoring (TDM) offers the possibility to individualize and
improve a patient*s pharmacological treatment, based on the measurement of drug
concentrations in biological samples. In clinical practice, TDM comprises the
measurement of one or more drug concentrations associated with the
administration of the dose of a certain drug. Dependent on the drug exposure
measured, the dose of the drug may be increased or decreased. This is expected
to result in a change in exposure, which in turn may yield more efficacy or
less toxicity. In this way, the aim of TDM is to improve exposure aiming at
maximizing efficacy and minimizing toxicity for an individual patient.

Conventionally, TDM is performed with blood or plasma obtained by venous blood
sampling. This method is associated with several challenges such as i) the need
for the patient to travel to the hospital or health center; ii) special
conditions for sample transport to guarantee stability of the analyte and to
decrease the biohazard risk; iii) sampling times not always representing the
preferable peak or trough concentrations; iv) the method being invasive and v)
delay of the outcome of the analyses with regard to the outpatient visit.
The Dried Blood Spot (DBS) may offer a solution for all these challenges. To
perform the DBS technique, only a small amount of blood is needed and this
sample can easily be obtained via a finger prick is put on a piece of filter
paper, can be taken at home and is sent to the laboratory by post mail.
Patients or their caregivers can perform the sampling at the appropriate time
in the concentration curve, e.g. at the time of the trough concentration, while
avoiding an extra visit to the hospital or health center. When arriving at the
hospital for a meet-up with the physician, adaptation of the dose based on the
already available drug concentration is directly possible and a delay
introduced by conventional sampling procedures is thereby avoided.

The majority of the patients on antifungal and immunosuppressive agents are
treated at home, for very long periods, which is an obstacle to continuous
monitoring of drug exposure. After solid organ transplantation, patients are
required to take life-long immunosuppressive agents. Therapy with antifungal
agents requires weeks but usually several months. It is important to monitor
and protect this vulnerable population from start of therapy onwards, as not
reaching target concentrations is associated with higher mortality.
DBS is thought to offer benefits over plasma venous sampling for TDM. The main
purpose of the PROTECT (Personalized treatment of immunosuppressive and
antifungal drugs through continuous home based monitoring with Dried Blood Spot
sampling techniques in pediatric patients) study is to improve therapeutic
management and patient participation in pediatric patients treated with
antifungal and immunosuppressive agents. PROTECT is mainly financed by a ZonMW
grant *Goed Gebruik Geneesmiddelen*.
Four patient organizations are actively involved in the PROTECT study, i.e.
Nierpatiënten Vereniging Nederland (NVN), Vereniging voor zeldzame en
genetische aandoeningen (VSOP), Vereniging ouders, kinderen en kanker (VOKK)
and Stichting voor Afweerstoornissen (SAS).

Primairy
To clinically validate a finger prick DBS method compared to conventional
venous sampling for the analysis of 5 immunosuppressive and 4 azole antifungal
drugs in the pediatric population.

Secondairy
• Feasibility of the novel finger prick DBS method in the pediatric population
will be assessed. This includes scoring of relevant characteristics
(attributes) of blood drawing methods for TDM, evaluation of the experience and
attitude of both patients and parents regarding finger prick DBS sampling and
evaluation of the understanding of the written instructions provided for
performing the finger prick at home. The data obtained in this validation study
will be used for the implementation of the DBS in therapeutic drug monitoring
(TDM) being a less invasive procedure, and as a base for a discrete
choice-experiment as part of the HTA.
• To design an inventory of types of costs that will be incurred in the process
of DBS-based and conventional TDM as a preparation step for later health
economic analysis.
• Data from this study will be used to construct a population pharmacokinetic
model to optimize dosing and design new guidelines.

This is an observational multi-centre study in which DBS sampling is compared
with conventional sampling for TDM in a steady state situation.

As in this study no change in therapy is performed it possesses a minimal risk.
The risks associated with a finger prick are pain at the puncture site and risk
of bleeding. The risks associated with venous blood sampling are similar (e.g.,
risk of infection, risk of hematomas and pain and/or discomfort at the puncture
site). For inpatients: only patients with a venous catheter can participate.
For outpatients: only patients who have their blood drawn for regular patient
care will be included, with one one moment of blood drawing. In addition, only
experienced personnel will perform the study.

This study focuses on those immunosuppressive agents and azole antifungals that
are currently subject of TDM and most used in the pediatric population. As
children are not small adults, unexpected findings are possible to arise,
warranting validation in this target population. As to factors that are known
to influence the outcome of the measurement through DBS by means of a finger
prick, hematocrit is of particular relevance, and this parameter was shown to
be different and more variable in the pediatric population. This has been
recognized by other groups too and experts in the field emphasize the need for
clinical validation in the target population. In the neonatal setting, various
clinical validations for analysis of DBS have been performed, e.g. Suyagh et
al. (2010) performed a validation of metronidazole in premature neonates by
means of heel prick DBS.
Clearly, information on feasibility of DBS sampling in children and on costs
relevant to DBS sampling in children can only be obtained through actual
sampling in children.
The four involved patient organizations support the PROTECT proposal and
underline the need for this novel sampling method especially in the pediatric
population.