RESUMO
A liquid chromatography-tandem mass spectrometry (LC-MS/MS) analytical method for the measurement of the novel heart rate-lowering drug ivabradine and its major metabolite, S-18982, was cross-validated in the plasma of eight healthy cats. Plasma concentrations were then determined after single and repeated oral administration of ivabradine. Individual plasma concentrations versus time from each cat were used in compartmental analysis using the commercially available software WinNonlin. Both ivabradine and S-18982 reached their maximum concentrations of 103.33 and 3.86 ng/mL within 1 h. Following repeated administration, areas under the plasma concentration-time curves for ivabradine and S-18982 did not significantly increase. Two-compartmental and one-compartmental models with first-order input and elimination provided the best fit to the data for ivabradine and S-18982, respectively. Both models were combined to produce a single 4-compartment model characterizing ivabradine and S-18982 pharmacokinetics. The results of this study indicate that repeated oral doses of ivabradine produced plasma drug concentrations suitable for 12-h dosing intervals in healthy cats. Furthermore, the analytical assay and combined ivabradine/S-18982 model provide tools for further evaluation of ivabradine pharmacokinetics and pharmacodynamics in future studies in cats.