A previous entry detailed Dried Blood Spot Analysis: Preclinical Pros and Cons. Additional preclinical considerations include the ambiguity of acceptance by global regulatory agencies, none of which have issued definitive rulings on how they’ll handle New Drug Applications (NDA) that use the technique. Furthermore, although validation standards and regulatory guidance exist for liquid assays, many of the suggested parameters (e.g., reproducibility after freezing and thawing of samples) are not applicable to dried blood spot analyses, where samples are dried and stored at room temperature.
Physical parameters also affect dried matrix spotting. Blood spot size is partly dependent on hematocrit, the percentage of the blood volume composed of red blood cells. Hematocrit is not only variable between individuals but also varies daily within a given individual. Therefore given sample dilution based on variable hematocrit, analyte levels can vary widely between individual samples. As a further development, the heightened analytical sensitivity used in nonclinical drug development (relative to the more traditional clinical uses) has mandated more stringent standards for blotter paper.
Another preclinical use for this technique is analysis of other limited-volume body fluids (e.g., synovial fluid, tears, and cerebrospinal fluid), some of which have not been routinely sampled preclinically in the past due to inefficient methodology. For example, arthritis mostly affects biomarkers in synovial fluid. In rodent preclinical models, however, only a few microliters of synovial fluid exist in each joint. This has forced preclinical scientists to rely on surrogate markers in the animal’s plasma to monitor drug efficacy/toxicity. By utilizing dried matrix spotting, rodent joints can now be sampled directly. Furthermore, due to the generally colorless nature of alternate fluids, proprietary paper treatments have been identified to allow for color changes that facilitate spot identification. As an additional benefit, alternate fluid analyses lack the inherent variability due to hematocrit.
Dried matrix spotting is quickly overcoming perceived challenges. It remains to be seen whether the heralded FDA Strategic Priorities for 2011-2015, which include advancing the field of Regulatory Science, will promote advancement/acceptance of dried matrix spotting as part of it’s mandate to develop new tools, standards, and approaches to assess the safety, effectiveness, quality, and performance of FDA-regulated products. Stay tuned…!
Source: Drug Discovery and Development.