Background To assess drug adherence of patients with hypertension, an analytical method was developed and validated using ultra performance liquid chromatography tandem mass spectrometry (UPLC–MS/MS). The method includes eight frequently prescribed antihypertensive drugs from four classes and their active metabolites: angiotensin converting enzyme inhibitors enalapril and perindopril (active metabolites respectively enalaprilate and perindoprilate), angiotensin II receptor blockers losartan (with the active metabolite losartan carboxylic acid) and valsartan, calcium channel blockers amlodipine and nifedipine and diuretics hydrochlorothiazide and spironolactone (with the active metabolite canrenone).
Methods The antihypertensive drugs were analyzed using a simple and fast sample preparation protocol with protein precipitation followed by chromatographic separation using a gradient elution on a reversed phase column. Mass spectrometric detection was conducted by applying both positive and negative electrospray ionization (ESI+/ESI−) and selected reaction monitoring mode (MS/MS). Only 50 μl of plasma sample is needed for the simultaneous quantification of all 12 compounds within 6 min run-to-run analysis time. Enalapril-d5 was applied as internal standard for all compounds except hydrochlorothiazide (internal standard: Hydrochlorothiazide-13C,d2).
Results The method was validated according to FDA guidelines. Matrix effects were examined using the method of Matuszewski. Correlation coefficients were higher than 0.995 for all compounds. Intra- and inter-day accuracies were <15% for all analytes except spironolactone (−16.8%) in the established linear range. Intra- and inter-day precision were <15% for all analytes. As a result of the lower sensitivity of hydrochlorothiazide, the lowest three calibration levels were excluded.
Discussion/Conclusions The described method is suitable for the simultaneous quantitative analysis of the most commonly used antihypertensive drugs and their corresponding active metabolites. Major advantages are minimal sample volume and clean up and a short runtime. The method is now available to monitor drug adherence of patients with resistant hypertension in our hospital.

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Keywords Antihypertensive drugs, Drug adherence, Therapeutic drug monitoring, UPLC–MS/MS
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Journal Journal of Chromatography. B, Analytical Technologies in the Biomedical and Life Sciences
van der Nagel, B.C, Versmissen, J, Bahmany, S, van Gelder, T, & Koch, B.C.P. (2017). High-throughput quantification of 8 antihypertensive drugs and active metabolites in human plasma using UPLC–MS/MS. Journal of Chromatography. B, Analytical Technologies in the Biomedical and Life Sciences, 1060, 367–373. doi:10.1016/j.jchromb.2017.06.029