As drug development programs progress into the clinic, the continued use of DBS provides additional benefits and cost savings. The simplified, less invasive blood sampling (finger/heel prick) is much more patient friendly than blood draws, especially for pediatric studies and in critically ill patients. The shipping, handling, and storage costs are also greatly reduced because DBS is safe and can be stored at room temperature.
Unlike liquid blood or plasma, DBS does not need to be handled as a biohazard since pathogens like HIV and hepatitis B are inactivated. Biohazardous samples are not only expensive to ship, but special training and licensing are also required. In addition, certain countries will not let blood samples be sent out of the country because they are biohazardous. The use of DBS can overcome these barriers.
Sample handling is much easier using DBS because the sample does not need to be centrifuged for plasma harvesting and then transferred to secondary tubes for freezing. Finally, refrigeration is not needed during transport or for storage as the DBS can be stored at room temperature. Normally, specialized couriers are needed to ship samples in dry ice, and for large Phase II/III clinical trials that require thousands of samples to be shipped from different sites, this process can be very expensive using liquid blood. The reduced amount of specialized equipment at clinical sites (refrigerated centrifuge, monitored freezers, etc.) also makes DBS technology extremely valuable when conducting clinical studies in emerging countries.
Increasingly Sensitive Technologies
At Aptuit, we have developed and fully validated more than 50 preclinical and clinical assays using DBS for different classes of compounds, some of which have been used in support of regulatory studies. In addition, we have developed an assay for a commercial drug that has demonstrated extremely high sensitivity—five picograms per mL. To achieve this sensitivity, we had to use hydrophilic interaction liquid chromatography (HILIC), which is a version of normal-phase liquid chromatography that offers a significant increase in sensitivity in mass spectrometry analysis over conventional techniques. Although HILIC technology is not new, the use of HILIC in DBS analysis represents an innovative approach.
We have demonstrated that the use of HILIC in DBS analysis can overcome the biggest limitation of DBS—difficulty reaching the lower limit of quantification levels due to limited sample volume. The development and validation of this clinical method provides evidence that the poor sensitivity of analytical assays, which made DBS inapplicable in extremely low dose clinical studies, is now less than an issue.
The limitations of DBS relate to the small size of the samples collected. Bioanalytical method development and validation is more laborious because various card types and additional parameters need to be assessed. Target sensitivity may be an issue for compounds that are administered at a very low therapeutic dose or those that are inhaled. In addition, it may be very difficult—and risky—for companies to switch from blood draws to DBS for clinical studies if blood draws were used in the preclinical stage of development because the data obtained is not directly comparable. In such cases bridging studies would be necessary, but regulatory agencies have not provided guidance on such an approach.
We have developed a new technique called dried plasma spotting (DPS) that collects plasma on filter paper instead of whole blood. DPS, which can be considered a natural progression of DBS, has a significant advantage for compounds in the later stages of the drug development process with a long history of analyses conducted in plasma: the switch from liquid plasma to DPS would make bridging studies unnecessary because the data generated in plasma and in DPS are directly comparable.
Compared to DBS, DPS requires more complex handling that is similar to liquid plasma, but there is still a significant cost savings due to simplified shipment and storage of samples at room temperature.
DBS sampling is increasingly of interest to pharmaceutical companies that appreciate its ethical, safety, quality, and economical benefits.