Characterization of hERG K+ channel inhibition by the new class III antiarrhythmic drug cavutilide

Cavutilide (niferidil, refralon) is a new class III antiarrhythmic drug which effectively terminates persistent atrial fibrillation (AF; 84.6% of patients, mean AF duration 3 months) and demonstrates low risk of torsade de pointes (1.7%). ERG channels of rapid delayed rectifier current(IKr) are the primary target of cavutilide, but the particular reasons of higher effectiveness and lower proarrhythmic risk in comparison with other class III IKr blockers are unclear. The inhibition of hERG channels expressed in CHO-K1 cells by cavutilide was studied using whole-cell patch-clamp. The present study demonstrates high sensitivity of IhERG expressed in CHO-K1 cells to cavutilide (IC50 = 12.8 nM). Similarly to methanesulfonanilide class III agents, but unlike amiodarone and related drugs, cavutilide does not bind to hERG channels in their resting state. However, in contrast to dofetilide, cavutilide binds not only to opened, but also to inactivated channels. Moreover, at positive constantly set membrane potential (+ 60 mV) inhibition of IhERG by 100 nM cavutilide develops faster than at 0 mV and, especially, - 30 mV (τ of inhibition was 78.8, 103, and 153 ms, respectively). Thereby, cavutilide produces IhERG inhibition only when the cell is depolarized. During the same period of time, cavutilide produces greater block of IhERG when the cell is depolarized with 2 Hz frequency, if compared to 0.2 Hz. We suggest that, during the limited time after injection, cavutilide produces stronger inhibition of IKr in fibrillating atrium than in non-fibrillating ventricle. This leads to beneficial combination of antiarrhythmic effectiveness and low proarrhythmicity of cavutilide.

Efficiency and safety of the modified protocol for cardioversion of atrial fibrillation using the antiarrhythmic drug niferidil. First results of clinical use

Introduction

Atrial fibrillation (AF) is one of the most common forms of arrhythmia. Niferidil is a new russian class III antiarrhythmic drug that has shown high efficiency in restoration of sinus rhythm (SR) in persistent AF (87%) in clinical trials that is non-inferior to direct current cardioversion. Currently, a three-stage scheme of drug administration is used (10 μg/kg – 10 μg/kg – 10 μg/kg). In a number of patients, SR restored before the end of injection of the first dose of the drug, which suggests the effectiveness of an even lower dose (5 μg/kg) of the drug, which has not been studied in clinical trials.

Objective

To evaluate the effectiveness and safety of the modified protocol of niferidil administration in patients with paroxysmal and persistent AF.

Materials and methods

This study included 100 patients with paroxysmal (n=20) and persistent AF (n=80), 53 of them were men, mean age 63±12 years. After exclusion of contraindications, all patients received niferidil according to the following scheme. The initial dose of niferidil was 5 μg/kg of body weight, if AF did not terminate after 15 minutes (min.), niferidil was additionally administered at a dose of 5 μg/kg (total dose of 10 μg/kg). If SR was not restored patients received subsequent injections of niferidil 10 μg/kg, each after 15 min. (maximal total dose of 30 μg/kg). Injections were discontinued in case of SR restoration, QTc >500 ms or proarrhythmia. All patients underwent continuous ECG monitoring within 24 hours to assess effectiveness and safety of niferidil.

Results

SR was restored in 94 out of 100 patients (cumulative effectiveness of niferidil in doses up to 30 μg/kg was 94%). 37% of patients restored SR after a dose of 5 μg/kg. All 20 patients with paroxysmal AF restored SR within 24 hours. Niferidil restored SR in 74 of 80 patients with persistent AF (92,5%). 26 (32,5%) of them restored SR after administration of 5 μg/kg dose, 62% – after 10 μg/kg dose and 92,5% – after 30 μg/kg dose. In none of the cases was there any development of life-threatening ventricular arrhythmias. Prolongation of the QTc >500 ms was recorded in 16 patients (16%). In all patients, prolongation of the QTc interval to the maximum values was noted within the first 6 hours from the start of drug administration. Bradyarrhythmias after SR recovery were reported in 11 patients (11%). In all cases sinus bradycardia was asymptomatic and resolved within a few minutes without any therapeutic intervention.

Conclusions

The modified protocol of cardioversion allows SR to be restored in a significant number of AF patients lower doses of niferidil. The drug is highly effective in the treatment of paroxysmal AF, while in many patients, SR recovery occurs after injection of lowest (5 μg/kg and 10 μg/kg) doses of the drug. Despite the prolongation of the QTc interval >500 ms in a number of patients, in none of the cases the development of Torsades de pointes observed.

Funding Acknowledgement

Type of funding sources: None.