Electrophysiologic Mechanism of Typical Atrial Flutter Termination by Nifekalant: Effect of a Pure IKr-Selective Blocking Agent

Comparison of the efficacy and safety of different doses of nifekalant in the instant cardioversion of persistent atrial fibrillation during radiofrequency ablation

Nifekalant has been used in the treatment of atrial arrhythmia recently. However, there is no consensus on the preferable nifekalant dose to treat atrial fibrillation (AF). The purpose of this study was to explore efficacy and safety of different doses of nifekalant in the cardioversion of persistent AF. The study was a single-centre, randomized controlled trial. All subjects received nifekalant or placebo intravenously, and the nifekalant was given at the dosage of 0.3, 0.4 or 0.5 mg/kg. Primary efficacy end-point: compared with 0.3 mg group, the rate of cardioversion to sinus rhythm from AF in 0.4 and 0.5 mg group was higher. The 0.4 and 0.5 mg/kg doses were associated with a similar magnitude of efficacy (P > .05). Secondary efficacy end-point: termination rates of AF in the group of 0.4 mg and 0.5 mg were higher than 0.3 mg. Primary safety end-point: the rate of Torsades de Pointes or ventricular fibrillation was numerically lower in the 0.4 mg group than 0.5 mg group (P = .02). Secondary safety end-point: The rates of the majority of other common drug-related adverse events in the group of 0.5 and 0.4 mg were higher than the 0.3 mg group. A 0.4 mg/kg dose of intravenous nifekalant may be recommended during the radiofrequency ablation for persistent AF considering the benefit-risk profile.

Population pharmacokinetic/pharmacodynamic modelling of nifekalant in healthy Chinese volunteers

Nifekalant is a class III antiarrhythmic drug, and its major adverse effect is prolongation of the QT interval. This study analysed data generated from a pharmacokinetic (PK) study to develop a population PK/pharmacodynamics (PD) model for describing the relationship between plasma concentrations and prolongation of the QT interval over time following intravenous administration of nifekalant. This open-labelled, phase I clinical study comprised two dose level groups of eight healthy Chinese volunteers. Concentrations of nifekalant in plasma samples collected at set time-points were determined using a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method. A PK/PD model was constructed using a non-linear mixed-effects approach (Phoenix NLME 8.1). Furthermore, demographic covariates of the model were investigated and a concentration factor (Conc^Ɵ) was introduced as the only covariate which improved the performance of the model. The final population PK model exhibited one-order elimination with two-compartment distribution and adequately described nifekalant plasma concentrations over time. The QT interval prolongation was best described by an indirect effect model with an inhibition build-up effect, representing the relationship between plasma concentrations and effect. The final population PK/PD model may facilitate more accurate predictions of the drug profile in clinical settings in the future.