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Dried blood spots (DBS) have been considered as complementary matrix in sports drug testing for many years. Especially concerning substances prohibited in-competition only, the added value of DBS collected concomitantly with routine doping control urine samples has been debated, and an increasing potential of DBS has been discussed in the scientific literature. To which extent and under which prerequisites DBS can contribute to enhanced anti-doping efforts is currently evaluated. As a proof-of-principle, two analytical applications, one targeting cocaine/benzoyl ecgonine and the other prednisone/prednisolone, are presented in this perspective to indicate potential added value but also presently existing limitations of the DBS approach.

The knowledge on PK behavior of steroid drugs such as prednisolone or prednisone has indeed been expanding but at a rather slow pace. First, convenient, rapid, and specific determination of plasma levels of these steroids was largely indebted to the breakthrough of high performance liquid chromatography (HPLC). Second, prednisolone is non-linearly protein-bound. Since unbound prednisolone is the biologically active compound, only the measurement of this free fraction in plasma is relevant. Third, the short half-life of prednisolone precludes to reach steady-state levels and requires determination of the area under the concentration-time curve. Fourth, prednisolone and prednisone are mutually convertible. Intravenous prednisolone, however, is administered as a pro-drug ester, which renders comparison and interpretation of reported PK data of both agents unreliable. A poignant lack of awareness and knowledge regarding catabolism, clearance mechanisms, and elimination route of steroids fuels the ongoing controversy that surrounds adjunctive corticosteroid therapy in patients with chronic or acute inflammatory disease. This particular patient population is also more prone to develop early and significant kidney dysfunction, necessitating extra-renal support. A better understanding of steroid PK/PD, preferentially guided by HPLC measurement of plasma steroid concentrations, likely will have direct clinical implications, for instance by adapting steroid doses in IHD or implementing higher dose regimens during CRRT.