Candesartan

Reference substances of lercanidipine, telmisartan and valsartan were obtained from Sigma-Aldrich GmbH (Steinheim, Germany). Amlodipine and candesartan, as well as the deuterated internal standards (IS) diazepam-d₅, lorazepam-d₄ and nordiazepam-d₅ were purchased from LGC Standards GmbH (Wesel, Germany).
Acetonitrile was obtained from Karl Roth GmbH (Karlsruhe, Germany) and ethyl acetate from AppliChem (Darmstadt, Germany). Further chemicals and solvents used were supplied by Sigma-Aldrich GmbH (Steinheim, Germany). All reagents and solvents were either of analytical or LC grade.

Amlodipine besylate was purchased from Pfizer (Karlsruhe, Germany); canrenone from the European Directorate for the Quality of Medicines & HealthCare (Strasbourg, France); bisoprolol fumarate, metoprolol tartrate, carvedilol, candesartan, valsartan, olmesartan, torasemide, and a diazepam-d5 solution (1 mg/mL in methanol) from LGC Standards (Wesel, Germany); atorvastatin-d5 calcium salt from Alsachim (Shimadzu Group, Illkirch Graffenstaden, France); and methanol, acetonitrile (ACN), diethyl ether, ethyl acetate, and natrium sulfate from VWR International GmbH (Darmstadt, Germany), as well as ammonium formate and formic acid from Merck KGaA (Darmstadt, Germany). All chemicals were of analytical grade. Water was purified with a Millipore filtration unit (18.2 Ω × cm water resistance) from Merck (Darmstadt, Germany). Drug-free pooled human blank plasma was obtained from a local blood bank. The analysis of human samples was approved by the local ethics committee to assess medication adherence using toxicological analyses objectively and complied with the Declaration of Helsinki. All patients provided written informed consent.