Determination of nifurtimox in dog plasma by stable-isotope dilution LC-MS/MS.

BACKGROUND: Nifurtimox is a 5-nitrofuran derived antiprotozoal drug used to treat diseases caused by trypanosomes including Chagas' disease and sleeping sickness (African trypanosomiasis). Available methods for the determination of nifurtimox in plasma are tedious and of low sensitivity. For the first time, an isotope dilution HPLC/MS/MS method for the sensitive quantitation of nifurtimox down to 10.0 µg/l in plasma is described. RESULTS: Protein precipitation was used for sample preparation. Samples were analyzed on a standard triple quadrupole tandem mass spectrometer. The validated concentration range covers 10.0 µg/l (LLOQ) to 5000 µg/l. Interassay accuracy and precision (%CV) ranged from 98.4 to 101%, and 2.61 to 10.1%, respectively. CONCLUSION: The method consists of very simple sample preparation and provides unmatched sensitivity, high reproducibility and robustness enabling analysis of large sample numbers. Method performance met current guidelines on bioanalytical method validation.

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

BACKGROUND: 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. RESULTS: 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. CONCLUSION: The method proved to be selective, specific, sufficiently sensitive, highly reproducible and robust for the analysis of large numbers of samples.