Determination of finerenone – a novel, selective, nonsteroidal mineralocorticoid receptor antagonist – in human plasma by high-performance liquid chromatography-tandem mass spectrometry and its application to a pharmacokinetic study in venous and capillary human plasma

A straightforward and rapid high-performance liquid chromatography–tandem mass spectrometry (HPLC–MS/MS) assay allowing the sensitive and selective quantitation of finerenone (BAY 94–8862) in lithium heparin human plasma is described. Finerenone is a novel, selective, nonsteroidal mineralocorticoid receptor antagonist that is in phase III clinical trials for the treatment of chronic kidney disease. Finerenone quantitation is performed after addition of its stable isotope-labelled internal standard (ISTD) by protein precipitation with acidified acetonitrile followed by HPLC–MS/MS separation and detection. The determination of finerenone concentrations was validated for a plasma volume of 0.100 mL and subsequently also for a lower plasma volume of 0.010 mL, collected e.g. in paediatric studies. The analytical range was from 0.100 µg/L (lower limit of quantification) to 200 µg/L (upper limit of quantification). Inter-day accuracy was 99.7–105.0% for the plasma volume of 0.100 mL and 101.1–104.5% for the plasma volume of 0.010 mL. Inter-day precision was ≤ 7.0%, independent of the extracted plasma volume. A moderate, concentration-independent matrix effect on ionisation was observed for both finerenone and its ISTD of 0.535–0.617, which is fully compensated by the ISTD (ISTD-normalised matrix factors were 0.98–1.03). The assay was successfully applied with both validated plasma volumes to a clinical phase I study in which the pharmacokinetics of 20 mg finerenone were compared in capillary plasma (0.010 mL) and venous plasma (0.100 mL) in a concentration range from the lower limit of quantification to 310 µg/L (capillary plasma) and 252 µg/L (venous plasma). The area under the plasma concentration versus time curve was similar in both matrices, while maximum concentrations were 37% higher in capillary plasma. In conclusion, capillary sampling should not bias pharmacokinetic exposure estimates compared with venous plasma values, if limited to sampling times in the distribution and elimination phases of finerenone.