Blood was drawn for the analysis of candesartan at 0 (pre-dose), 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 10, 12, and 48 h post dose. The plasma concentrations of candesartan were measured via ultra-highperformance liquid chromatography (UPLC) using a Waters ACQUITY UPLC TM System (Waters, Milford, MA, USA) coupled with a tandem mass spectrometer (Waters Xevo TM TQ MS; Waters, Milford, MA, USA). Samples were prepared by protein precipitation preceding separation and injected into the LC-MS/MS system comprising a 1.7-lm Waters ACQUITY UPLC Ò BEH C18 column (2.1 mm ID 9 50 mm L; Waters, Milford, MA, USA). A multiple reaction monitoring (MRM) mode was used for the quantification of candesartan at m/ z 441.00 ? 263.18 and candesartan-d 5 at m/ z 446.10 ? 268.20. The linear calibration curve ranged from 5 to 1000 ng/mL. The concentrations of candesartan in the quality control samples were 15, 400, and 750 ng/mL. The determination coefficient (r 2 ) for the calibration curves was C 0.99. The bioassay for candesartan was validated on the basis of the within-batch and between-batch precision and accuracy of the quality control samples. The relative standard deviation was less than 15%. Amlodipine Blood was drawn for the analysis of amlodipine at 0 (pre-dose), 1, 2, 3, 4, 5, 6, 7, 8, 10, 12, 24, 48, and 72 h post dose. The plasma concentrations of amlodipine were measured using a Waters ACQUITY UPLC TM System coupled with a Waters Xevo TM TQ-XS mass spectrometer. Samples were prepared by protein precipitation prior to separation and injected into the 1.7-lm Waters ACQUITY UPLC Ò BEH C18 (2.1 mm ID 9 50 mm L) column of the LC-MS/MS system. An MRM mode was used for the quantification of amlodipine at m/z 409.20 ? 238.15 and amlodipine-d 4 at m/z 413.20 ? 238.15. The linear calibration curves ranged from 0.05 to 50 ng/mL. The concentrations of amlodipine in the quality control samples were 0.15, 15, and 37.5 ng/mL. The bioassay for amlodipine was validated on the basis of the within-batch and between-batch precision and accuracy of the quality control samples. The relative standard deviation was less than 15%.