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BackgroundThe inotropic drug levosimendan is often used as an individualized therapeutic approach perioperatively in cardiac surgery patients with cardiopulmonary bypass (CPB). Data regarding serum concentrations of levosimendan and its metabolites within this context is lacking.MethodsIn this retrospective descriptive proof-of-concept study, total serum concentrations (TSC) and unbound fractions (UF) of levosimendan and its metabolites OR-1896 and OR-1855 in cardiac surgery patients with CPB were measured using LC-ESI-MS/MS. Simulation of expected levosimendan TSC was performed using Pharkin 4.0. Serum NT-proBNP was assessed with ELISA.ResultsAfter levosimendan infusion (1.25 mg or 2.5 mg, respectively) after anaesthesia induction, a median TSC of 1.9 ng/ml and 10.4 ng/ml was determined in samples taken directly after surgery (T1). Median TSC of 7.6 ng/ml and 22.0 ng/ml, respectively, were simulated at T1. Whereas 1.1 ng/ml and 1.6 ng/ml TSC of OR-1896, respectively, was quantified the day after surgery (T2), TSC of the intermediate metabolite OR-1855 was mostly below the lower limit of quantification (LLOQ). The UF was 0.5% and 1.1% for levosimendan and 64.1% and 52.1% for OR-1896, respectively, with over half the samples being below LLOQ. NT-proBNP concentrations before surgery and T2 did not differ.DiscussionThe low TSC, UF and unchanged NT-proBNP levels in combination with high variation of serum levels between patients suggest a need for optimized dosing regimen of levosimendan combined with therapeutic drug monitoring for such an individualized approach. In addition, the differences between the measured and estimated concentrations may suggest a possible influence of CPB on levosimendan serum concentrations.

The calcium sensitizer levosimendan is used for the treatment of acute decompensated heart failure. A small portion (4–7%) of levosimendan is metabolized to the pharmacologically active metabolite OR-1896 via the inactive intermediate OR-1855. In addition, levosimendan has been shown to exert positive effects on the endothelium in vitro antagonizing vascular dysfunction and inflammation. However, the function of the levosimendan metabolites within this context is still unknown. In this study, we thus investigated the impact of the metabolites OR-1896 and OR-1855 on endothelial inflammatory processes in vitro. We observed a reduction of IL-1β-dependent endothelial adhesion molecule ICAM-1 and VCAM-1 as well as interleukin (IL) -6 expression upon levosimendan treatment but not after treatment with OR-1855 or OR-1896, as assessed by western blotting, flow cytometry, and qRT-PCR. Instead, the metabolites impaired IL-1β-induced ROS formation via inactivation of the MAPK p38, ERK1/2, and JNK. Our results suggest that the levosimendan metabolites OR-1896 and OR-1855 have certain anti-inflammatory properties, partly other than levosimendan. Importantly, they additionally show that the intermediate metabolite OR-1855 does, in fact, have pharmacological effects in the endothelium. This is interesting, as the metabolites are responsible for the long-term therapeutic effects of levosimendan, and heart failure is associated with vascular dysfunction and inflammation.

Levosimendan is used in severe chronic cardiac insufficiency, also within the peri-operative setting. Real-life pharmacokinetic data in surgical patients is lacking, making therapeutic drug monitoring (TDM) of levosimendan, its pharmacologically active metabolite OR-1896, and its intermediate OR-1855 important. A simultaneous highly sensitive quantification of levosimendan and its metabolites in small-volume samples has not yet been described. Here, levosimendan (LLOQ 0.450 nM), OR-1896, and OR-1855 (LLOQ both 1.0 nM) were successfully quantified by LC-ESI-MS/MS after liquid-liquid extraction in 300 µL of blood. A short C8 column under reversed-phase conditions enabled simultaneous and fast quantification of levosimendan in the negative and the metabolites in the positive ionization mode in a single run within 2 min. Interestingly and unexpectedly, constitutional isomers of levosimendan metabolites with identical mass transitions and similar retention times were observed in surgical patients’ samples, which we identified as the metamizole metabolites 4-aminoantipyrine and 4-acetamidoantipyrine. A longer C8 column and a modified mobile phase enabled selective quantification of all analytes in a single run within 7 min. We developed, validated, and applied highly sensitive LC-ESI-MS/MS methods for simultaneous quantification of levosimendan and its metabolites, enabling efficient TDM of cardiac surgery patients even with additional metamizole administration.