Simultaneous Quantification of Azole Antimycotics in Quantitative Dried Blood Spots: A Step Toward Home Sampling for...

Home sampling for therapeutic drug monitoring (TDM) shows promise as a valuable tool, particularly for stable patients with limited access to health care. Quantitative dried blood spot (qDBS) technology has emerged as a promising solution. This study aimed to develop a method for simultaneous quantification of fluconazole, voriconazole, isavuconazole, posaconazole, itraconazole, and hydroxyitraconazole and to investigate key technical issues such as transport stability and the conversion formulas between different matrices.

The extraction protocol was optimized using spiked qDBS samples with a series of methanol/water and acetonitrile/water mixtures. Stability tests were performed at 2-8°C and 45°C to mimic environmental conditions of regular mail delivery. Linear regression for converting voriconazole concentrations from qDBS to plasma samples was established using 101 routine TDM samples.

The optimal extraction solvent was acetonitrile/water (70/30). The method validation demonstrated excellent linearity (R 2 > 0.99), accuracy (recovery of 92.1%-104.2%), and precision (intraday and interday variability <3.3% and 5.7%, respectively). Stability tests confirmed that all azole drugs remained stable, even at 45°C for 7 days. Conversion formula indicated that qDBS sample concentration was equivalent to that in plasma, as supported by Bland-Altman analysis, which revealed a mean bias of -8.49% and 95% limits of agreement ranging from -20.11% to +3.13%.

This study established a sensitive, accurate, precise, and robust quantification method in qDBS samples containing only 10 μL of whole blood. Stability tests showed that samples could be safely mailed, offering a cheaper alternative to cold chain logistics. A conversion formula using routine TDM samples was developed, providing a straightforward and cost-effective approach for establishing a conversion formula that is potentially applicable to other TDM analytes. This study represents an in vitro analytical validation, and future clinical research is needed to translate the analytical method from bench to bedside.