This blog begins with a review of an article published by David Sciberras et al at UCB Biopharma and PRA Health sciences in the January 2019 issue of Pharmacology Research and Perspectives. The authors reported on the results of a Phase 1 clinical PK study of a drug under development for the treatment of infantile spasms.
The paper is entitled “A pharmacokinetic study of radiprodil oral suspension in healthy adults comparing conventional venous blood sampling with two microsampling techniques.” It describes a study where PK safety and tolerability of an infant formula was evaluated on healthy adult volunteers.
The study was a success and the investigators reported that the microsampling technique allowed the potential for collection of samples at home or in remote areas where access to a clinic might be challenging. The authors added, “The key limitation of the study's relevance to infants is that it was conducted in adults.”
Image: D Sciberras et al, UCB Biopharma & PRA Health sciences, Jan. 2019, Pharmac Res & Perspect.
The above review of this excellent 2019 paper demonstrates how critically important bridging is when developing methods involving different matrices. Indeed, the US Food and Drug Administration (FDA) recommended in their 2018 Bioanalytical Method Validation Guidelines (05/24/18) pertaining to blood spots: “Correlative studies with traditional sampling should be conducted during drug development.”
In the case of the UCB bridging study, all matrices independent of location (capillary or venous) and type (plasma or blood), showed statistically equivalent data. However, this may not always be the case. Indeed, even within this study, there was a notable difference in absolute concentration when comparing dried blood vs. plasma. This was attributed to blood-to-plasma partitioning ratios as a root cause.
Indeed, B:P ratio can be very significant and must always be accounted for when validating methods with capillary blood. For example, a published study by David J. Marshall et al (reviewed in a previous blog), showed that when comparing steroid hormone levels in dried whole blood from VAMS extracts to wet plasma, the plasma bound hormones showed a negative bias in the VAMS extracts. This is because these hormones are not usually found in the hematocrit (HCT) in significant quantities.
As a result, to arrive at plasma equivalent values, the group employed a HCT compensation measure (by measuring Hb levels as a surrogate HCT marker) to correct for each datapoint. Indeed, this approach has been used and reported on in many other studies.
There is another consideration when bridging from tractional venous plasma to dried capillary blood: sampling site location (venous vs. capillary). In the UCB study, sampling location was found to not affect the results, but in the Marshall study, one hormone (testosterone) out of the three evaluated showed a significant difference in concentration between both locations.
A final point is that preservatives used in venous blood samples can, on occasion, affect the results. This was recently reported on by Merck Pharmaceuticals, where EDTA was found to affect stable labelled internal standard levels.
Indeed, the need for such a bridge is highlighted in the recently published Official International Association for Therapeutic Drug Monitoring and Clinical Toxicology Guidelines, where it states “It is essential that the use of this anticoagulant does not impact the obtained results, and that the stability of calibrators and QCs reflects that of real samples. Hence, we strongly advise to compare in an early-stage results obtained from a non-anticoagulated sample with results from patient samples anticoagulated with different anticoagulants.”
As volumetric dried blood microsampling continues to gain traction, it is critical that extra care is taken to fully validate studies employing these technologies. When conducted appropriately, as evidenced by the studies highlighted in this technical blog, robust assays can be fully validated, giving researchers a choice as to how to collect high-quality samples from hard-to-reach cohorts.
This study paper 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 review, visit the original article published in the journal, Pharmacology Research and Perspectives.
You can access this paper and others on studies using microsampling in our Technical Resource Library.