Integrated pharmacokinetics and pharmacodynamics of the novel calcium sensitizer levosimendan as assessed by systolic time intervals.

Background: Levosimendan is a new calcium sensitizer, acting calcium-dependently on cardiac troponin C. In the present study pharmacokinetic-pharmacodynamic interrelations of levosimendan were assessed. Subjects and methods: Ten healthy subjects (22 - 27 years) were given single doses of 2 mg of levosimendan in 4 different formulations: intravenous (i.v.), conventional tablet (CT), conventional capsule (CC), and slow-release tablet (SR) on different days. Systolic time intervals and impedance cardiography were recorded up to 4 hours post drug. Plasma concentrations of levosimendan and its metabolite OR-1855 were analyzed using HPLC. Hysteresis loops were constructed by connecting the effect-concentration points in time order. In addition, pharmacokinetic-pharmacodynamic modelling was performed with the i.v. data. Results: The i.v. administration, giving a maximal levosimendan concentration of 180 ng x ml -1 , increased heart rate by 8 beats min -1 and cardiac output by 18%. It shortened heart rate corrected electromechanical systole QS2i by 23 ms, indicating a fairly strong positive inotropic effect. The conventional oral formulations (giving maximal drug concentrations of about 70 - 80 ng x ml -1 ) increased heart rate by 4 - 5 beats min -1 and cardiac output by 5 - 8%, while QS2i shortened by 9 - 13 ms. The SR formulation resulted in low drug concentrations and generally weaker effects than the other formulations. The bioavailability of CT and CC was 83 and 87%, while that of SR was only 31%. QS2i showed counter-clockwise hysteresis after all formulations (p < 0.01). The mean equilibration half-time (In(2)/ke0) after i.v. administration was 9.6 min. Only after SR, OR-1855 was detected in appreciable amounts in plasma, the highest value being 2.2 ng x ml -1 which occurred 24 hours after drug intake. Conclusion: In conclusion, the pharmacokinetic-dynamic behavior of the inotropy index QS2i indicates an equilibration delay of levosimendan, which most probably reflects the time the drug requires to distribute from plasma to its cardiac site of action. The deviant kinetic-dynamic profile of the oral slow-release formulation suggests a different absorption pattern of levosimendan from this formulation.