The inotropic drug levosimendan is often used off-label perioperatively in cardiac surgery patients with cardiopulmonary bypass (CPB). Data regarding serum concentrations of levosimendan and its metabolites within this context is lacking.
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 retrospectively measured using LC-ESI-MS/MS. Simulation of expected levosimendan TSC was performed using Pharkin 4.0. Serum NT-proBNP was assessed with ELISA.
After prolonged levosimendan infusion (1.25 mg or 2.5 mg, respectively) after induction of anaesthesia, 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. No difference in NT-proBNP concentrations before surgery and T2 was detected.
The low TSC, UF and unchanged NT-proBNP levels suggest a need for dose adjustments of levosimendan in this off-label range. In addition, the differences between the measured and estimated concentrations may suggest a possible influence of a CPB on levosimendan serum concentrations. Due to high variation of serum levels between patients, an optimized dosing regimen combined with therapeutic drug monitoring may be advisable.