Closing the gap - development of an analytical methodology using volumetric absorptive microsampling of finger prick blood followed by LC-HRMS/MS for adherence monitoring of antihypertensive drugs.

Volumetric absorptive microsampling (VAMS), an emerging microsampling technique, is a promising tool for adherence monitoring. This study focused on development of an analytical methodology to improve VAMS-based strategies for adherence assessment by analyzing angiotensin-converting-enzyme (ACE) inhibitors, loop diuretics, a potassium-sparing diuretic, and a thiazide diuretic. Development included sample preparation, chromatographic conditions, mass spectrometry settings, validation, and demonstrating proof of concept. Quantification of analytes, by name furosemide, hydrochlorothiazide, lisinopril, torasemide, and the active metabolites, canrenone, enalaprilat, and ramiprilat in finger prick blood (FPB), was validated based on international guidelines. Selectivity, carryover, and within/between-run accuracy and precision were in accordance with the recommendations. The matrix effect was evaluated at three different hematocrit levels (HT: 20%, 40%, 60%) and the coefficients of variation did not exceed 15%. Dilution integrity (1:10 and 1:20) was given for all analytes except lisinopril, yet for lisinopril, the therapeutic range was already covered by the calibration range. Long-term stability in VAMS tips was tested for 2 weeks at 24 °C in the dark and revealed no degradation of analytes. The proof of concept was performed by analyzing 35 intakes of ACE-inhibitors and diuretics in 18 VAMS and matched plasma samples. Hereby, determined concentration in FPB and plasma cannot be used interchangeably, and thus specific reference ranges for whole blood must be established. Nevertheless, the VAMS-based strategy was shown to be suitable for assessing adherence of all classes of antihypertensive drugs used in the guidelines to manage hypertension.