how to use capillary blood samples in pediatric PK studies

Pharmacokinetic (PK) studies investigate the absorption and movement of drugs within the body. Since children absorb and process drugs differently than adults do, PK studies have to be done on children to determine they receive safe and effective doses.

Such pediatric studies of new drugs, however, are fraught with concerns. Parents understandably do not wish for their children to be harmed or to suffer unnecessary pain because of the new drug study itself.

How PK Studies Are Conducted

PK studies used to require large volumes of blood to be collected from study participants on a routine basis. The blood samples were typically obtained via the venipuncture method, in which a phlebotomist draws blood from a vein in the arm. In children, veins are small and can be very hard to find, often requiring multiple needle pokes. This can cause significant pain and emotional trauma for both the child getting their blood drawn and their parents. Additionally, if a large volume of blood is needed for lab analysis, the child can incur a risk of anemia.

Gentler Collection of Blood Samples for Pediatric PK Studies

To avoid these blood collection challenges in pediatric studies, a technique called dried blood spot (DBS) sampling was developed. In the early 1960s, DBS was standardized for use in newborn screening for detecting genetic disorders. This innovation introduced the concept of a quick heel-stick with a lancet to draw a few drops of blood via microsampling. The "micro-sized" blood drops placed on filter paper could be used to replace the more invasive venipuncture blood draws for certain lab tests.

While the standard DBS method is gentler and more convenient, it has its challenges. The hematocrit in the blood affects the amount that is absorbed onto the DBS filter paper. This results in irregular amounts of drugs contained within the DBS samples, which can skew lab results. For this reason, standard DBS is not always suitable in PK studies.

Volumetric Microsampling for PK Studies

Volumetric microsampling is a more recent blood sampling method that was developed as an advance over standard DBS for use in situations where consistent and precise sample size is critical. The hemaPEN^® is a volumetric microsampling device that uses the finger-stick method to collect four volumetrically identical capillary samples.

After a single finger-stick with a lancet, the hemaPEN is placed directly onto the blood drop that forms at the fingertip. The blood is wicked up inside the device via its four glass capillary tubes and then transferred onto its four DBS filter papers inside. The four DBS filter papers in the device are pre-punched and are sized to absorb precisely 2.74 µL for each DBS sample. Thus, a single sampling event produces 4 x 2.74 µL DBS samples, for a total volume of 10.96 µL ready for reliable lab analysis.

Volumetric Absorptive Microsampling for PK Studies

There also is a technique called volumetric absorptive microsampling where the blood from a finger-stick or heel-stick is absorbed onto an absorbent sponge tip with volumetric precision.

The Neoteryx Mitra^® device based on VAMS^® technology is available with three different sizes of an absorbent VAMS tip, which can be dipped into whole blood (or plasma, urine, saliva, etc.) to absorb between 5 and 30 microliters.

This precision eliminates the problem of hematocrit bias, as demonstrated in multiple studies. After sample collection, the sampled devices are air dried and can be stored at room temperature.

Centrifugation is not required with the VAMS method, which saves process steps and time in a PK Study. A supernatant liquid is then added, and the samples are analyzed on a mass spectrometer for the drug levels.

As with animal studies that are part of preclinical research, the use of microsampling with capillary blood samples saves time and money during pediatric PK studies as well as decreasing pain and anxiety in children. In the world of pediatric PK studies, microsampling provides a "less is more" solution.

Image credits: Trajan, Neoteryx