Evaluation of pharmacokinetic and pharmacodynamic profiles and tolerability after single (2.5, 5, or 10 mg) and repeated (2.5, 5, or 10 mg bid for 4.5 days) oral administration of ivabradine in healthy male Korean volunteers

The Functional Role of Hyperpolarization Activated Current (I f) on Cardiac Pacemaking in Human vs. in the Rabbit Sinoatrial Node: A Simulation and Theoretical Study

The cardiac hyperpolarization-activated “funny” current (I_f), which contributes to sinoatrial node (SAN) pacemaking, has a more negative half-maximal activation voltage and smaller fully-activated macroscopic conductance in human than in rabbit SAN cells. The consequences of these differences for the relative roles of I_f in the two species, and for their responses to the specific bradycardic agent ivabradine at clinical doses have not been systematically explored. This study aims to address these issues, through incorporating rabbit and human I_f formulations developed by Fabbri et al. into the Severi et al. model of rabbit SAN cells. A theory was developed to correlate the effect of I_f reduction with the total inward depolarising current (I_total) during diastolic depolarization. Replacing the rabbit I_f formulation with the human one increased the pacemaking cycle length (CL) from 355 to 1,139 ms. With up to 20% I_f reduction (a level close to the inhibition of I_f by ivabradine at clinical concentrations), a modest increase (~5%) in the pacemaking CL was observed with the rabbit I_f formulation; however, the effect was doubled (~12.4%) for the human I_f formulation, even though the latter has smaller I_f density. When the action of acetylcholine (ACh, 0.1 nM) was considered, a 20% I_f reduction markedly increased the pacemaking CL by 37.5% (~27.3% reduction in the pacing rate), which is similar to the ivabradine effect at clinical concentrations. Theoretical analysis showed that the resultant increase of the pacemaking CL is inversely proportional to the magnitude of I_total during diastolic depolarization phase: a smaller I_f in the model resulted in a smaller I_total amplitude, resulting in a slower pacemaking rate; and the same reduction in I_f resulted in a more significant change of CL in the cell model with a smaller I_total. This explained the mechanism by which a low dose of ivabradine slows pacemaking rate more in humans than in the rabbit. Similar results were seen in the Fabbri et al. model of human SAN cells, suggesting our observations are model-independent. Collectively, the results of study explain why low dose ivabradine at clinically relevant concentrations acts as an effective bradycardic agent in modulating human SAN pacemaking.

HCN4 current during human sinoatrial node-like action potentials

BACKGROUND

Despite the many studies carried out over the past 40 years, the contribution of the HCN4 encoded hyperpolarization-activated 'funny' current (I_f) to pacemaker activity in the mammalian sinoatrial node (SAN), and the human SAN in particular, is still controversial and not fully established.

OBJECTIVE

To study the contribution of I_f to diastolic depolarization of human SAN cells and its dependence on heart rate, cAMP levels, and atrial load.

METHODS

HCN4 channels were expressed in human cardiac myocyte progenitor cells (CMPCs) and HCN4 currents assessed using perforated patch-clamp in traditional voltage clamp mode and during action potential clamp with human SAN-like action potential waveforms with 500-1500 ms cycle length, in absence or presence of forskolin to mimic β-adrenergic stimulation and a -15 mV command potential offset to mimic atrial load.

RESULTS

Forskolin significantly increased the fully-activated HCN4 current density at -140 mV by 14% and shifted the steady-state activation curve by +7.4 mV without affecting its slope. In addition, forskolin significantly accelerated current activation but slowed deactivation. The HCN4 current did not completely deactivate before the subsequent diastolic depolarization during action potential clamp. The amplitude of HCN4 current increased with increasing cycle length, was significantly larger in the presence of forskolin at all cycle lengths, and was significantly increased upon the negative offset to the command potential.

CONCLUSIONS

I_f is active during a human SAN action potential waveform and its amplitude is modulated by heart rate, β-adrenergic stimulation, and diastolic voltage range, such that I_f is under delicate control.

Pharmacokinetic profile of ivabradine hemisulfate sustained-release tablets administered in Chinese healthy volunteers: An open-label, randomized, single-dose, three-period crossover study

We aimed to determine the pharmacokinetics and safety of three single oral doses (5, 10 and 15 mg) of ivabradine hemisulfate sustained-release tablets in healthy Chinese volunteers. A total of 12 volunteers (six males and six females) were randomized to receive a single oral dose of ivabradine hemisulfate sustained-release tablets 5, 10 or 15 mg, with a 1-week washout between periods. Blood samples were collected at regular intervals from 0 to 48 h after drug administration, and the concentrations of ivabradine and N-desmethyl ivabradine were determined by HPLC-tandem mass spectrometry. Pharmacokinetic parameters were estimated by non-compartmental analysis. After administering single doses of 5, 10 and 15 mg, the mean maximum concentration (C_max ) levels of ivabradine were 4.36, 7.29 and 12.62 ng/mL, and the mean area under the curve from time 0 to 48 h (AUC_0-48 ) values were 55.66, 101.16 and 182.09 h·ng/mL, respectively. The mean C_max levels of N-desmethyl ivabradine were 1.05, 2.03 and 3.16 ng/mL, and the mean AUC_0-48 values were 20.61, 39.44 and 65.72 h·ng/mL, respectively. The median time of maximum concentration (T_max ) levels of ivabradine and N-desmethyl ivabradine were 5 h for all three doses tested. The pharmacokinetic properties of ivabradine hemisulfate sustained-release tablets were linear at doses from 5 to 15 mg. Ivabradine hemisulfate sustained-release tablet appears to be well tolerated in these healthy volunteers.

Ivabradine reversed nondipping heart rate in rats with l-NAME-induced hypertension

We hypothesized that decreasing elevated night-time heart rate (HR) in hypertension by administering a bradycardic agent (ivabradine) at bedtime could bring cardiovascular benefit. Since rats are nocturnal animals, they exhibit circadian rhythms phase-shifted relative to humans. Sixty-six Wistar rats were divided into non-diseased controls and rats with l-NAME-induced hypertension to compare the haemodynamic effects of daytime-dosed and night-time-dosed ivabradine. l-NAME-induced hypertension inverted the physiological 5.6% night-to-day HR dip to an undesirable HR rise by 11.1%. Ivabradine dosed at daytime (the rat's resting phase) reverted a night-to-day HR rise to HR dip by 14.2%. These results suggest a cardiovascular benefit of ivabradine dosed at the human's resting phase (night-time) for hypertensive patients with nondipping HR.

Role of ivabradine and heart rate lowering in chronic heart failure: guideline update

INTRODUCTION

This review summarizes the current management of heart failure (HF) in patients with reduced ejection fraction and the potential role of heart rate lowering agents in select populations, as recommended in the updated guidelines. Areas covered: PubMed was searched for studies that evaluated the role of heart rate lowering or ivabradine in HF management. Expert commentary: Targeting heart rate may offer benefit when added to renin-angiotensin aldosterone antagonists, and beta-blockers. Ivabradine is a heart rate lowering agent that acts on the funny current (I_f) in the sinoatrial node, thereby reducing heart rate without directly affecting cardiac contraction and relaxation. Clinical data from a phase III trial demonstrated that ivabradine reduced the composite end point of cardiovascular death or hospital admission for worsening systolic HF, while maintaining an acceptable safety profile in patients receiving standard of care therapy. These data, in addition to more recently published guidelines, suggest ivabradine as a promising new treatment option for lowering heart rate after optimizing standard therapy in select patients with chronic HF.

Ivabradine in Management of Heart Failure: a Critical Appraisal

Elevated resting heart rate has been linked to poor outcomes in patients with chronic systolic heart failure. Blockade of funny current channel with ivabradine reduces heart rate without inotropic effects. Ivabradine was recently approved by US Food and Drug Administration for patients with stable, symptomatic chronic heart failure (HF) with left ventricular ejection fraction (LVEF) ≤35 %, who are in sinus rhythm with resting heart rate (HR) ≥ 70 bpm and either are on maximally tolerated doses of beta-blockers, or have a contraindication to beta-blockers. This article will review and evaluate the data supporting the use of ivabradine in patients with HF and explore its mechanisms and physiologic effects.

Population plasma and urine pharmacokinetics of ivabradine and its active metabolite S18982 in healthy Korean volunteers

Ivabradine, a selective inhibitor of the pacemaker current (If ), is used for heart failure and coronary heart disease and is mainly metabolized to S18982. The purpose of this study was to explore the pharmacokinetics (PK) of ivabradine and S18982 in healthy Korean volunteers. Subjects in a phase I study were randomized to receive 2.5, 5, or 10 mg of ivabradine administered every 12 hours for 4.5 days, and serial plasma and urine concentrations of ivabradine and S18982 were measured. The plasma PK of ivabradine was best described by a 2-compartment model with mixed 0- and first-order absorption, linked to a 2-compartment model for S18982. The introduction of interoccasional variabilities and period as covariate into absorption-related parameters improved the model fit. Urine data have been applied to estimate renal and nonrenal clearance, enabling a more detailed description of the elimination process. We developed a population PK model describing the plasma and urine PK of ivabradine and S18982 in healthy Korean adult males. This model might be useful for predicting the plasma and urine PK of ivabradine, potentially helping to identify the optimal dosing regimens in various clinical situations.

An evaluation of the pharmacokinetics and pharmacodynamics of ivabradine for the treatment of heart failure

INTRODUCTION

Ivabradine is a new heart-rate-lowering drug; the aim of this review was to analyze its role in heart failure (HF).

AREAS COVERED

This systematic review on the role of ivabradine in HF is based on material searched and obtained through Pubmed and Medline up to September 2013.

EXPERT OPINION

Heart rate (HR) is a risk factor in patients with HF, and its reduction is considered an important goal of therapy. The BEAUTIFUL trial demonstrated the benefits of ivabradine on prognosis (only on ischemic endpoints) in patients with coronary artery disease (CAD) and left ventricular systolic dysfunction (LVSD) and HR ≥ 60 bpm. In the SHIFT trial, which enrolled patients with LVSD, HF and HR ≥ 70 bpm, ivabradine administration (on top of guideline-based therapy, including β-blockers [BB]) was associated with a reduction of cardiovascular death and hospitalizations for HF, but BB were underutilized. Further studies are needed to test the efficacy of ivabradine in CAD patients with high HR and to shed light on the comparison between ivabradine and a more aggressive therapy with higher doses of BB in HF patients.