Determination of riociguat and its major human metabolite M-1 in human plasma by stable-isotope dilution LCMS/MS

Riociguat (BAY 63-2521) is an oral NO-independent as well as NO-synergistic stimulator of soluble guanylate cyclase (sGC) for the treatment of pulmonary hypertension. BAY 60-4552 (M-1) is its pharmacologically active major metabolite. An isotope dilution LC-ESI-MS/MS method has been developed and validated for the simultaneous determination of riociguat and M-1 in lithium heparinized human plasma. The validated concentration range covers 0.500 μg/l (LLOQ) to 100 μg/l (ULOQ) for both analytes. Interassay accuracy and precision (%CV) for both analytes ranged from 92.7 to 111% and from 2.61 to 9.89%, respectively. The method proved to be selective, specific, sufficiently sensitive, highly reproducible and robust for the analysis of large numbers of samples.