Inhibition of the myocardial Ca2+ inward current by the class 1 antiarrhythmic agent, cibenzoline

Mid-ventricular obstruction occurred in hypertrophic left ventricle of heterozygous Fabry's disease-Favorable effects of cibenzoline: A case report

A 54-year-old woman visited our hospital because of palpitation and dizziness. Systolic ejection murmur, Levine IV/VI, was heard at the left sternal border and atrial gallop was auscultated at apex. Echocardiogram demonstrated diffuse hypertrophy of the left ventricular walls extending to the apex. The left ventricular walls increased symmetrically; the septal and the posterior wall measured approximately 26 mm and 30 mm in thickness, respectively. Apical two-chamber views revealed a narrow outflow of the left ventricular cavity at apex with a distinct convergence zone, where color flow Doppler imaging showed turbulent jet flow from mid to late systole. The leukocyte α-galactosidase A activity was lower than normal. Percutaneous endomyocardial biopsy showed specific change for Fabry's disease by electron microscopy. On cardiac catheterization, mid-ventricular resting pressure gradient of approximately 90 mmHg was shown. This pressure gradient dramatically disappeared after intravenous administration of 70 mg of cibenzoline. We describe a rare case of Fabry's disease that revealed diffuse hypertrophy having dynamic obstruction at mid-left ventricle, like mid-ventricular obstruction, and the administration of cibenzoline had beneficial effects on pressure gradient of mid-left ventricle.

Pharmacodynamics of cibenzoline-induced hypoglycemia in rats

Hypoglycemia is one of the serious adverse effects induced by cibenzoline (CBZ), an antiarrhythmic agent. In order to clarify the pharmacodynamics of CBZ-induced hypoglycemia, CBZ was administered intravenously to conscious rats at a dose of 5, 10 or 20 mg/kg and serum samples were collected periodically to determine the concentrations of CBZ, insulin and glucose. The pharmacokinetics of CBZ showed nonlinear characteristics and could be described by a two-compartment model with Michaelis-Menten elimination kinetics. CBZ induced a rapid increase in the serum concentration of insulin. As the CBZ dose was increased, a greater hypoglycemic effect occurred. The indirect response model was applied to account for the CBZ-induced increase in insulin secretion and the subsequent decrease in serum glucose. A linear relationship was assumed between the serum concentration of CBZ and its stimulating effect on insulin secretion. A nonlinear relationship was assumed between the serum concentration of insulin and its stimulating effect on the elimination of serum glucose. The time courses of serum concentrations of CBZ, insulin and glucose after intravenous injection of CBZ could be described by the pharmacokinetic and pharmacodynamic model developed. This approach will be useful for the identification of variable factors related to CBZ-induced hypoglycemia.

Comparison of acute reduction in left ventricular outflow tract pressure gradient in obstructive hypertrophic cardiomyopathy by disopyramide versus pilsicainide versus cibenzoline

Negative inotropic agents are often administered to decrease the left ventricular (LV) pressure gradient in patients with obstructive hypertrophic cardiomyopathy (HC). Little information is available regarding comparisons of the effects on LV pressure gradient among negative inotropic agents. The present study compared the decrease in the LV pressure gradient at rest in patients with obstructive HC after treatment with pilsicainide versus treatment with disopyramide or cibenzoline. The LV pressure gradient and LV function were assessed before and after the intravenous administration of each drug. In 12 patients (group A, mean pressure gradient 90 ± 24 mm Hg), the effects of disopyramide, propranolol, and verapamil were compared. In another 12 patients (group B, mean pressure gradient 98 ± 34 mm Hg), a comparison was performed among disopyramide, cibenzoline, and pilsicainide. In group A, the percentage of reduction in the LV pressure gradient was 7.7 ± 9.9% with verapamil, 19.0 ± 20.2% with propranolol, and 58.6 ± 15.0% with disopyramide, suggesting that disopyramide was more effective than either verapamil or propranolol. In group B, the percentage of reduction in the LV pressure gradient was 55.3 ± 26.6% with disopyramide, 55.3 ± 20.6% with cibenzoline, and 54.7 ± 15.4% with pilsicainide, suggesting an equivalent effect on the LV pressure gradient for these 3 agents. In conclusion, these results indicate that the acute efficacy for the reduction of the LV pressure gradient at rest by pilsicainide (a pure sodium channel blocker) was equivalent to that of disopyramide or cibenzoline (combined sodium and calcium channel blockers). Accordingly, sodium channel blockade might be more important for reducing the LV pressure gradient at rest in patients with obstructive HC than calcium channel blockade or β blockade.

Effect of cibenzoline on biventricular pressure gradients in a pediatric patient with hypertrophic obstructive cardiomyopathy

This report presents the case of an 8-year-old male with biventricular hypertrophic obstructive cardiomyopathy who achieved a successful reduction of the pressure gradients by treatment with cibenzoline. Ultrasound echocardiography showed marked intraventricular septal hypertrophy and left midventricular and right ventricular outflow obstructions. A cardiac catheterization revealed left midventricular and right outflow obstructions associated with pressure gradients of 100 and 35 mmHg, respectively. An intravenous injection of 28 mg (1.4 mg/kg) cibenzoline immediately improved the biventricular pressure gradients. Therefore, oral cibenzoline treatment was initiated, the dose was increased to 150 mg/day, and both pressure gradients remained low, without any complications at the time of discharge, 4 months later.

Effect of Intravenous Administration of Cibenzoline on Left Ventricular Diastolic Pressures in Patients With Hypertrophic Cardiomyopathy Its Relationship to Transmitral Doppler Flow Profiles

BACKGROUND

Cibenzoline is able to improve left ventricular (LV) diastolic dysfunction in patients with hypertrophic cardiomyopathy (HCM), but the exact mechanism remains to be determined.

METHODS AND RESULTS

The present study was designed to elucidate the effect of intravenous administration of 1.4 mg/kg of cibenzoline on aortic and LV pressures, and transmitral Doppler flow pattern in 7 patients with hypertrophic obstructive cardiomyopathy (HOCM) and 9 patients with hypertrophic nonobstructive cardiomyopathy (HNCM). Before and at the end of the administration, aortic and LV pressures, LV pressure gradient (LVPG) and transmitral Doppler velocity profiles were examined. After the administration of cibenzoline, LV minimal and end-diastolic pressures decreased from 9+/-4 mmHg to 1+/-5 mmHg (p=0.0049) and from 22+/-7 mmHg to 14+/-5 mmHg (p=0.0106) in patients with HOCM, and from 9+/-5 mmHg to 5+/-3 mmHg (p=0.0036) and from 20+/-6 mmHg to 14+/-3 mmHg (p=0.0033) in patients with HNCM. LVPG decreased in all patients with HOCM. E-wave velocity increased, A-wave velocity decreased, and thus the E/A ratio increased from 0.77+/-0.29 to 1.20+/-0.48 (p=0.0004).

CONCLUSIONS

Reduction of LV diastolic pressures by intravenous administration of cibenzoline may be related to an improvement in the E/A ratio in patients with HCM.

Cibenzoline improves coronary flow velocity reserve in patients with hypertrophic obstructive cardiomyopathy

The effect of cibenzoline, a class-Ia antiarrhythmic drug, on coronary flow velocity reserve (CFVR) was examined in patients with hypertrophic cardiomyopathy using transthoracic Doppler echocardiography. Coronary flow velocity reserve was assessed in 11 patients with hypertrophic obstructive cardiomyopathy (HOCM) and 12 patients with hypertrophic nonobstructive cardiomyopathy (HNCM), before and after the intravenous administration of cibenzoline (1 mg/kg). Coronary hyperemia was induced by an intravenous infusion of adenosine triphosphate and CFVR was calculated as the ratio of hyperemic to basal mean coronary diastolic flow velocity. At baseline, CFVR was significantly correlated with left ventricular outflow tract pressure gradient (LVPG) in patients with HOCM (r = 0.67, P < 0.03). In patients with HOCM, administration of cibenzoline significantly improved impaired CFVR (2.0 +/- 0.8 to 3.0 +/- 1.0, P < 0.001), and reduced LVPG (55 +/- 30 to 23 +/- 18 mmHg, P < 0.001), while CFVR remained unchanged in patients with HNCM (2.6 +/- 0.9 to 2.9 +/- 0.8, P not significant). Cibenzoline not only reduces LVPG but also improves CFVR in patients with HOCM. In addition left ventricular outflow obstruction plays an important role in impaired coronary circulation in patients with HOCM.

Antiarrhythmic drug cibenzoline attenuates left ventricular pressure gradient and improves transmitral Doppler flow pattern in patients with hypertrophic obstructive cardiomyopathy caused by midventricular obstruction

BACKGROUND

Recent interventional and surgical therapies to attenuate left ventricular pressure gradient (LVPG) can be difficult to perform in patients with hypertrophic obstructive cardiomyopathy (HOCM) caused by midventricular obstruction (MVO), owing to the risk of inducing or deteriorating mitral regurgitation.

METHODS AND RESULTS

The effects of the antiarrhythmic drug, cibenzoline, on LVPG and left ventricular (LV) diastolic function estimated by the change in the transmitral Doppler flow pattern were examined in 23 patients with HOCM and MVO. Hemodynamic changes 2 h after a single dose of 200 mg of cibenzoline and 3 months after oral administration of 300-450 mg of cibenzoline per day were examined. At 2 h after the treatment, LVPG decreased from 79+/-37 mmHg to 24+/-21 mmHg (p < 0.0001). E-wave velocity significantly increased and A-wave velocity significantly decreased, and thus the E/A ratio increased from 0.83+/-0.39 to 1.36+/-0.50 (p < 0.0001). After 3 months of treatment, LVPG remained decreased, and the E-wave and A-wave velocities and the E/A ratio remained improved.

CONCLUSIONS

Cibenzoline can attenuate LVPG and ameliorate LV diastolic dysfunction in patients with HOCM caused by MVO, which suggests a new strategy for the management of this condition.

Cibenzoline attenuates upregulation of Kv1.5 channel gene expression by experimental paroxysmal atrial fibrillation

Antiarrhythmic drugs exert their effects by inhibiting the ion channels of cardiomyocytes. However, these effects could also modify the ionic environment around them, and thereby affect the expression of ion channels, leading to biochemical enhancement or attenuation of the antiarrhythmic effects. To test this hypothesis, the physiological and biochemical effects of cibenzoline were evaluated in a rapid atrial pacing model in rats. In rats with rapid atrial pacing, pretreatment with cibenzoline significantly inhibited the increases in Kv1.5 mRNA at 2 hours and immunoreactive protein at 4 hours by 35 +/- 15% and 30 +/- 10%, respectively. These effects were observed only in the rapid atrial pacing group, not in the sham-operated group. With cibenzoline pretreatment, 4-hour rapid atrial pacing resulted in significant prolongation of the atrial refractory period compared to the untreated group even after removal of cibenzoline. In contrast, the sham and rapid atrial pacing model with and without cibenzoline pretreatment showed similar acute physiological responses to cibenzoline. In conclusion, in addition to the acute physiological effects, pretreatment with cibenzoline exerted pleiotropic effects of inhibition of Kv1.5 channel upregulation by rapid pacing, implying differences in the cibenzoline effects when administered before and after onset of paroxysmal atrial fibrillation.

Pharmacological cardioversion of atrial fibrillation: current management and treatment options

Atrial fibrillation (AF) is the most common form of arrhythmia, carrying high social costs. It is usually first seen by general practitioners or in emergency departments. Despite the availability of consensus guidelines, considerable variations exist in treatment practice, especially outside specialised cardiological settings. Cardioversion to sinus rhythm aims to: (i) restore the atrial contribution to ventricular filling/output; (ii) regularise ventricular rate; and (iii) interrupt atrial remodelling. Cardioversion always requires careful assessment of potential proarrhythmic and thromboembolic risks, and this translates into the need to personalise treatment decisions. Among the many clinical variables that affect strategy selection, time from onset is crucial. In selected patients, pharmacological cardioversion of recent-onset AF can be a safely used, feasible and effective approach, even in internal medicine and emergency departments. In most cases of recent-onset AF, pharmacological cardioversion provides an important--and probably more cost effective--alternative to electrical cardioversion, which can then be employed as a second-line therapy for nonresponders. Class IC agents (flecainide or propafenone), which can be safely used in hospitalised patients with recent-onset AF without left ventricular dysfunction, can provide rapid conversion to sinus rhythm after either intravenous administration or oral loading. Although intravenous amiodarone requires longer conversion times, it is still the standard treatment for patients with heart failure. Ibutilide also provides good conversion rates and could be used for AF patients with left ventricular dysfunction (were it not for high costs). For long-lasting AF most pharmacological treatments have only limited efficacy and electrical cardioversion remains the gold standard in this setting. However, a widely used strategy involves pretreatment with amiodarone in the weeks before planned electrical cardioversion: this provides optimal prophylaxis and can sometimes even restore sinus rhythm. Dofetilide may also be capable of restoring sinus rhythm in up to 25-30% of patients and can be used in patients with heart failure. The potential risk of proarrhythmia increases the need for careful therapeutic decision making and management of pharmacological cardioversion. The results of recent trials (AFFIRM [Atrial Fibrillation Follow-up Investigation of Rhythm Management] and RACE [Rate Control versus Electrical Cardioversion for Persistent Atrial Fibrillation]) on rate versus rhythm control strategies in the long term have led to a generalised shift in interest towards rate control. Although carefully designed studies are required to better define the role of pharmacological rhythm control in specific AF settings, this alternative option remains a recommendable strategy for many patients, especially those in acute care.

Cibenzoline, an ATP-sensitive K(+) channel blocker, binds to the K(+)-binding site from the cytoplasmic side of gastric H(+),K(+)-ATPase

1. Cibenzoline, (+/-)-2-(2,2-diphenylcyclopropyl-2-imidazoline succinate, has been clinically used as one of the Class I type antiarrhythmic agents and also reported to block ATP-sensitive K(+) channels in excised membranes from heart and pancreatic beta cells. In the present study, we investigated if this drug inhibited gastric H(+),K(+)-ATPase activity in vitro. 2. Cibenzoline inhibited H(+),K(+)-ATPase activity of permeabilized leaky hog gastric vesicles in a concentration-dependent manner (IC(50): 201 microM), whereas no effect was shown on Na(+),K(+)-ATPase activity of dog kidney (IC(50): >1000 microM). Similarly, cibenzoline inhibited H(+),K(+)-ATPase activity of HEK-293 cells (human embryonic kidney cell line) co-transfected with rabbit gastric H(+),K(+)-ATPase alpha- and beta-subunit cDNAs (IC(50): 183 microM). 3. In leaky gastric vesicles, inhibition of H(+),K(+)-ATPase activity by cibenzoline was attenuated by the addition of K(+) (0.5 - 5 mM) in a concentration-dependent manner. The Lineweaver-Burk plot of the H(+),K(+)-ATPase activity shows that cibenzoline increases K(m) value for K(+) without affecting V(max), indicating that this drug inhibits H(+),K(+)-ATPase activity competitively with respect to K(+). 4. The inhibitory effect of H(+),K(+)-ATPase activity by cibenzoline with normal tight gastric vesicles did not significantly differ from that with permeabilized leaky gastric vesicles, indicating that this drug reacted to the ATPase from the cytoplasmic side of the membrane. 5. These findings suggest that cibenzoline is an inhibitor of gastric H(+),K(+)-ATPase with a novel inhibition mechanism, which inhibits gastric H(+),K(+)-ATPase by binding its K(+)-recognition site from the cytoplasmic side.

Antiarrhythmic drug, cibenzoline, can directly improve the left ventricular diastolic function in patients with hypertrophic cardiomyopathy

The effect of cibenzoline on left ventricular diastolic function was investigated in patients with hypertrophic cardiomyopathy (HCM). Before and 2 h after an oral administration of 200 mg of cibenzoline, echocardiographic, apexcardiographic and gated radionuclide angiographic studies were performed in 12 patients with hypertrophic obstructive cardiomyopathy (HOCM) and 7 with hypertrophic nonobstructive cardiomyopathy (HNCM). After administration of cibenzoline, the left ventricular pressure gradient decreased from 96+/-33 mmHg to 29+/-22 mmHg (<0.0001). Fractional shortening decreased from 53.3+/-7.5 to 45.4+/-6.2% (p=0.0008) in patients with HOCM and from 49.9+/-8.7 to 40.9+/-7.5% (p=0.0039) in patients with HNCM. On the other hand, E-wave velocity increased and A-wave velocity decreased in both groups. The time between the second heart sound and O point was shortened from 253+/-53 to 176+/-21 ms (p<0.0001) in patients with HOCM and from 245+/-54 to 185+/-44 ms (p=0.0050) in patients with HNCM. The time to peak filling rate was shortened from 248+/-79 to 190+/-40 ms (p=0.0072) in patients with HOCM and from 218+/-33 to 163+/-26 ms (p=0.0052) in patients with HNCM. These results indicate that in patients with HCM, cibenzoline suppresses left ventricular systolic function, but can markedly improve left ventricular diastolic dysfunction through its direct action.

Profiles of aprindine, cibenzoline, pilsicainide and pirmenol in the framework of the Sicilian Gambit. The Guideline Committee for Clinical Use of Antiarrhythmic Drugs in Japan (Working Group of Arrhythmias of the Japanese Society of Electrocardiology)

The Vaughan Williams classification has been used widely by clinicians, cardiologists and researchers engaged in antiarrhythmic drug development and testing in many countries throughout the world since its initial proposal in the early 1970s. However, a major criticism of the Vaughan Williams system arose from the extent to which the categorization of drugs into classes I-IV led to oversimplified views of both shared and divergent actions. The Sicilian Gambit proposed a two-dimensional tabular framework for display of drug actions to solve these problems. From April to December 1996, members of the Guideline Committee met to discuss pharmacologic profiles of 4 antiarrhythmic drugs (aprindine, cibenzoline, pilsicainide, and pirmenol) that were not included in the original spreadsheet but are used widely in clinical practice in Japan. The discussion aimed to fit the drug profiles into the Gambit framework based on all the important literature published to date regarding the actions of the 4 drugs. This report is a summary of that deliberation.

Na+ channel blocking effects of cibenzoline on guinea-pig ventricular cells

The effects of cibenzoline on transmembrane action potentials were examined in right ventricular papillary muscles and in single ventricular myocytes isolated from guinea-pig hearts. In papillary muscles, cibenzoline > or = 3 microM caused a significant decrease in the maximum upstroke velocity (Vmax) of the action potential without affecting the action potential duration. The inhibition of Vmax was enhanced at higher stimulation frequencies. In the presence of cibenzoline, trains of stimuli at rates > or = 0.2 Hz led to a use-dependent inhibition of Vmax. The time constant for Vmax recovery (tauR) from the use-dependent block was 26.2 s. The use-dependent block of Vmax with cibenzoline was enhanced and tauR was shortened when the resting potential was depolarized by high (8, 10 mM) [K+]o. The curve relating membrane potential and Vmax in single myocytes was shifted by cibenzoline (10 microM) in a hyperpolarizing direction by 7.1 mV. In myocytes treated with cibenzoline (10 microM), a 10-ms conditioning clamp to 0 mV caused a significant decrease in Vmax of the subsequent test action potential; the Vmax inhibition was enhanced modestly in association with a prolongation of the 0 mV clamp pulse duration. In the presence of cibenzoline (3 microM), application of a train of depolarizing pulses (10 ms, 200 ms) to myocytes from the resting level (-80 mV) to 0 mV resulted in a progressive Vmax reduction in a pulse number-dependent manner. Unlike glibenclamide (30 microM), cibenzoline (10 microM) did not prevent the hypoxia-induced shortening of action potential duration in papillary muscles. These findings indicate that the onset and offset kinetics of use-dependent Na+ channel block by cibenzoline are slow. Given its state dependence, cibenzoline may be a blocker of activated Na+ channels. The inhibitory action of this compound on the ATP-sensitive K+ current (I(K), ATP) would be minimal or negligible at concentrations causing sufficient Na+ channel block.

Effects of pirmenol on action potentials and membrane currents in single atrial myocytes

Electrophysiological effects of pirmenol hydrochloride (pirmenol) were investigated in single atrial myocytes obtained from rabbit and guinea-pig hearts by using a whole-cell clamp technique. Under current clamp conditions, pirmenol (2-30 microM) prolonged action potential duration in a concentration-dependent manner without affecting resting membrane potential in rabbit atrial myocytes. However, in the presence of 4-aminopyridine (4 mM), pirmenol (10 microM) failed to prolong the action potential duration further. Pirmenol also suppressed acetylcholine-induced hyperpolarization and action potential duration shortening, resulting in a significant prolongation of the action potential duration in the presence of acetylcholine. Under voltage clamp conditions, pirmenol (1-1000 microM) inhibited transient outward current (I(to)) in a concentration-dependent manner. The concentration for half-maximal inhibition (IC50) of pirmenol on I(to) was about 18 microM. Pirmenol did not show the use and frequency dependent inhibition of I(to). The voltage dependence of the steady-state inactivation of I(to) and the recovery from inactivation were not significantly affected by pirmenol. Pirmenol accelerated the inactivation of I(to) and blocked I(to) as an exponential function of time, consistent with a time-dependent open channel blockade. Pirmenol (30 microM) did not affect the inwardly rectifying K+ current significantly, but it decreased the voltage-dependent L-type Ca2+ current by about 20%. In guinea-pig atrial myocytes, both acetylcholine and adenosine induced a specific K+ current activated by GTP-binding proteins. Pirmenol suppressed both the acetylcholine- and adenosine-induced K+ current effectively. The IC50 of pirmenol for acetylcholine- and adenosine-induced current was about 1 and 8 microM, respectively. The present results suggest that pirmenol prolongs the action potential duration by primarily inhibiting the transient outward current in atrial myocytes. In addition, since pirmenol inhibits acetylcholine- and adenosine-induced K+ current, pirmenol may effectively prolong the action potential duration in atrial myocytes under various physiological conditions as in the whole heart or ischemia.

Class Ia antiarrhythmic drug cibenzoline: a new approach to the medical treatment of hypertrophic obstructive cardiomyopathy

BACKGROUND

The class Ia antiarrhythmic drug disopyramide relieves the outflow tract obstruction of hypertrophic obstructive cardiomyopathy (HOCM). Disopyramide, however, has several adverse effects, such as dysuria and thirst, resulting from its anticholinergic activity. A new class Ia antiarrhythmic drug, cibenzoline, has little anticholinergic activity. The aim of this study is to elucidate whether cibenzoline attenuates left ventricular pressure gradient (LVPG) in patients with HOCM.

METHODS AND RESULTS

Ten patients with HOCM (mean age, 59+/-12 years) participated in this study. LVPG and left ventricular functions were measured before and 2 hours after administration of a single oral dose of 150 or 200 mg cibenzoline. LVPG decreased from 123+/-60 to 39+/-33 mm Hg (P=.0026). The E/A ratio in transmitral Doppler flow increased from 1.20+/-0.84 to 2.00+/-1.72 (P=.029). Isovolumic relaxation time increased from 73+/-16 to 101+/-23 ms (P=.0026). Left ventricular diastolic dimension remained unchanged, but left ventricular systolic dimension enlarged significantly, from 21.6+/-2.4 to 26.2+/-3.3 mm (P=.0004). Fractional shortening decreased from 47.6+/-6.1% to 34.6+/-8.8% (P=.0007). Left ventricular ejection time index decreased significantly, and preejection period index increased in all the patients. Decreased LVPG remained maintained even in the long-term treatment with cibenzoline. Conclusions These results indicate that cibenzoline can markedly attenuate LVPG in patients with HOCM. A decrease in myocardial contractility seems to be closely related to a marked decrease in LVPG.

Electrophysiologic effects of a class I antiarrhythmic agent, cibenzoline, on the refractoriness and conduction of the human atrium in vivo

We investigated the effects of a class I antiarrhythmic drug, cibenzoline, on human atrial muscle in vivo. Electrophysiologic measurements were performed in 44 patients (mean age 49 +/- 15 years), before and after an intravenous infusion of cibenzoline 1.4 mg/kg in 5 min. Extrastimuli at a basic cycle length (BCL) of 500 ms were delivered from the right atrial appendage. The effective refractory period of the right atrium (ERP-A), the conduction time from the high right atrium to the coronary sinus, maximum conduction delay (Max. CD), repetitive atrial firing zone (RAFZ), fragmented atrial activity zone (FAAZ), and conduction delay zone (CDZ) were measured. Patients were divided into two groups according to whether repetitive atrial firing (RAF) was induced (group A, n = 18) or not (group B, n = 26). Cibenzoline increased ERP-A from 198 +/- 25 to 214 +/- 26 ms (p < 0.05) and decreased Max. CD from 55 +/- 23 to 43 +/- 19 ms (p < 0.05). There were significant decreases in the RAFZ (10 +/- 17 to 4 +/- 10 ms, p < 0.05), the FAAZ (20 +/- 25 to 12 +/- 18, ms p < 0.05), and the CDZ (41 +/- 21 to 32 +/- 19 ms, p < 0.05). Cibenzoline significantly increased ERP.A (186 +/- 25 to 212 +/- 26 ms, p < 0.05) in group A, but not in group B. There were significant decreases in the RAFZ [25 +/- 19 to 9 +/- 15 ms (p < 0.05) and FAAZ 22 +/- 29 to 11 +/- 21 ms, (p < 0.05)] in group A, but not in group B. The results suggest that cibenzoline can suppress paroxysmal atrial fibrillation by prolongation of ERP-A and may also have preferential effects on the substrate of atrial fibrillation and RAF.

Cibenzoline versus flecainide in the prevention of paroxysmal atrial arrhythmias: a double-blind randomized study

In a randomized, double-blind, parallel clinical trial, the authors tested and compared flecainide and cibenzoline, a new antiarrhythmic drug, on atrial arrhythmias. Sixty-eight patients (36 men, 32 women, mean age 62.5 +/- 1.6 years) with documented symptomatic paroxysmal atrial arrhythmias (fibrillation in 56, flutter in 12) were recruited and received either cibenzoline 260 mg/day (n = 33) or flecainide 200 mg/day (n = 35). Patients were assessed with physical examination, resting ECG, 24-hour ambulatory ECG recording, two-dimensional echocardiography, and standard biologic titrations before the inclusion day, and 3 months and 6 months after the randomization day. Sixteen patients were withdrawn (7 were lost to follow-up, 7 had side effects, 2 had another medical event). Seventeen patients had documented recurrence of atrial arrhythmia (9 in the cibenzoline group, 8 in the flecainide group) during the study. The efficacy of cibenzoline and flecainide for preventing recurrence of atrial arrhythmias was not significantly different (62.5% versus 71.4%). Eleven patients complained of one or more side effects (cibenzoline, n = 6; flecainide, n = 5), justifying leaving the trial in 6 cases (cibenzoline, n = 3; flecainide, n = 3). Two ventricular proarrhythmic effects were observed. No atrial proarrhythmic effects were reported. The efficacy of cibenzoline and flecainide for preventing atrial arrhythmia is good and similar during a follow-up period of 6 months. In view of these results, cibenzoline may be administered first to prevent atrial arrhythmia.

Effects of the Na+ antagonist cibenzoline on left ventricular function of postischemic hearts

The negative inotropic effect of antiarrhythmic drugs is a major drawback in antiarrhythmic drug therapy, especially in patients with reduced contractile function of the left ventricle. The circulatory and myocardial effects of the new class I antiarrhythmic drug (a Na+ antagonist), cibenzoline (2 mg/kg i.v.), were investigated in 47 open-chest rats with normal and postischemic myocardium (3 x 4 minutes of global ischemia). Hemodynamic measurements in the intact circulation and isovolumic registrations (peak isovolumic left ventricular systolic pressure and peak isovolumic dP/dtmax) were compared to saline controls. In rats with postischemic myocardium, cibenzoline caused a significant (p < 0.001) decrease in the cardiac output for 38%, in the dP/dtmax for 30%, and in the peak isovolumic dP/dtmax for 19% at the end of infusion (compared to the control). The heart rate was reduced by 22% (p < 0.001), the mean aortic pressure by 22% (p < 0.001), and the calculated systemic resistance by 20% (p < 0.001). In contrast to the results with postischemic myocardium, no important changes in the hemodynamics were detectable after an identical dose in normal animals without left ventricular dysfunction. The results indicate that standard doses of the Na+ antagonist cibenzoline may induce significant cardiodeperessant effects on postischemic left ventricles with reduced function.

Effects of cibenzoline, a new class Ia antiarrhythmic drug, on various membrane ionic currents and action potentials of guinea-pig ventricular cells

We examined the effects of cibenzoline, a new class Ia antiarrhythmic drug, on various membrane ionic currents and action potentials of guinea-pig single ventricular cells, using patch clamp techniques in whole-cell configuration. Action potentials and the membrane currents were evoked at a clamping rate of 0.2 Hz, and all experiments were performed at 32-33 degrees C. 1) Cibenzoline (5, 10 and 30 microM) decreased the Na+ current (INa), in a concentration-dependent manner. The concentration of the half-maximal inhibition (Kd) for INa was estimated to be 7.8 microM. 2) In addition to the inhibition of INa, this drug (5, 10, and 30 microM) decreased, in a concentration-dependent manner, all other membrane currents examined, such as L-type Ca2+ current (ICa), delayed rectifier K+ current (IK), and inward rectifier K+ current (IK1). The Kd (apparent dissociation constant) values were 14.4 microM for ICa, 23.0 microM for IK, and 33.7 microM for IK1 respectively. 3) Cibenzoline (5, 10, and 30 microns) significantly shortened the action potential duration measured at both 30% and 90% repolarization without altering the resting membrane potential. From these findings, we conclude that apart from potent inhibitory effects on INa, cibenzoline possesses multiple blocking effects on other currents, e.g., ICa, IK and IK1, with a different potency (INa > ICa > IK > IK1) and with essentially the same efficacy. These effects may explain, at least in part, the alleged, potent antiarrhythmic effects of this drug.

Inhibition of the ATP-sensitive potassium channel by class I antiarrhythmic agent, cibenzoline, in rat pancreatic beta-cells

1. Cibenzoline, a class I antiarrhythmic agent, was investigated for its effect on the ATP-sensitive K+ channel of pancreatic beta-cells by the patch clamp technique. 2. In perforated patch clamp experiments, cibenzoline depolarized the membrane of single beta-cells and thereafter, caused firing of action potentials in the presence of 2.8 mM glucose. 3. Cibenzoline inhibited the activity of the ATP-sensitive K+ channel in cell-attached recordings in the presence of 2.8 mM glucose and evoked repetitive fluctuations of the baseline current, apparently reflecting the action potentials of the beta-cell. 4. In whole-cell clamp experiments, time-independent outward current was induced by depleting cytoplasmic ATP with 0.1 mM ATP and 0.1 mM ADP in the solution contained in the pipette. The outward current was inhibited by cibenzoline in a dose-dependent manner in the concentration range of 1 microM to 100 microM and half maximum inhibition occurred at 1.5 microM. 5. Cibenzoline blocked substantially the ATP-sensitive K+ channel current when applied at the inner side of the membrane in isolated inside-out membrane patches. 6. It is concluded that cibenzoline blocks the ATP-sensitive K+ channel of pancreatic beta-cells and, thereby, stimulates insulin secretion at sub-stimulatory levels of glucose.

A clinical study of intravenous cibenzoline in selected patients with recent-onset atrial tachyarrhythmia

Twenty-five adult patients with sustained atrial tachyarrhythmia (ATA) and without heart failure were treated by intravenous cibenzoline, 1 mg/kg, as a slow bolus infusion, followed by a 8 mg/kg/24 h continuous infusion. Sinus rhythm conversion was observed in 18 patients (72 percent success rate). Severe adverse cardiac events were observed in only one patient (4 percent occurrence rate), as a wide QRS complex tachycardia finally requiring a semiemergency direct-current cardioversion. Two minor side effects were additionally observed. A similar population of 21 patients was conventionally treated with amiodarone, either given intravenously, 15 to 20 mg/kg/24 h, or orally, 30 mg/kg/24 h as a single dose. An identical success rate (15/21; 71 percent) was observed. Our results indicate that in selected patients with ATA, cibenzoline and amiodarone are highly effective for producing sinus rhythm conversion. We suggest that the former drug may be used as a first-line treatment. In case of failure, the latter may constitute an alternative to transthoracic electrical countershock.

Effects of hypoxia on the use-dependent inhibition of conduction velocity induced by cibenzoline in guinea pig ventricular myocardium

The use-dependent effects of cibenzoline, a new anti-arrhythmic drug, on the maximal rate of rise (Vmax) of the action potential and on conduction velocity, and their corresponding recovery kinetics were studied in isolated papillary muscles of guinea pigs under normal and hypoxic conditions. Standard microelectrode techniques were applied to monitor the action potential of the muscles and their conduction. Under control conditions, the amount of use-dependent block of Vmax, conduction velocity, and square of conduction velocity, induced by 10 mumol/L cibenzoline were 26.5 +/- 3.9, 13.8 +/- 1.4, and 25.6 +/- 2.4%, respectively; under hypoxic conditions, these values increased to 32.3 +/- 4.8, 19.7 +/- 1.2, and 35.5 +/- 2.0%, respectively. In the presence of 10 mumol/L cibenzoline, the mean values of time constants for the onset of the use-dependent inhibition of Vmax, conduction velocity, and the square of conduction velocity, during a 2-Hz stimulation, were 3.65 +/- 0.27, 2.77 +/- 0.33, and 2.56 +/- 0.26 seconds, respectively. Under hypoxic conditions, these values changed to 5.10 +/- 0.96, 3.05 +/- 0.44, and 2.84 +/- 0.39 seconds, respectively. The recovery time constants averaged 14.72 +/- 4.08 seconds (for Vmax), 22.23 +/- 3.78 seconds (for conduction velocity), and 23.17 +/- 13.38 seconds (for the square of conduction velocity) in the presence of 10 mumol/L cibenzoline, and 17.19 +/- 8.59 seconds (for Vmax), 15.77 +/- 2.37 seconds (for conduction velocity), and 16.82 +/- 2.61 seconds (for the square of conduction velocity) under hypoxic conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Cibenzoline inhibits diazoxide- and 2,4-dinitrophenol-activated ATP-sensitive K+ channels in guinea-pig ventricular cells

1. We have investigated the effects of diazoxide (a sulphonamide derivative) and cibenzoline (a class I antiarrhythmic drug) on ATP-sensitive K+ currents in guinea-pig ventricular cells, using whole-cell clamp techniques. 2. Diazoxide (50 microM) produced a marked shortening of action potential duration which was antagonized by 1 microM glibenclamide, an ATP-sensitive K+ channel blocker. 3. Diazoxide (50 microM) increased the quasi-steady state outward current elicited by a ramp voltage protocol (-20 mV s-1) at potentials positive to about -70 mV. This effect was completely prevented in the presence of glibenclamide (1 microM), thereby suggesting that diazoxide opens ATP-sensitive K+ channels. 4. Cibenzoline (5 microM) depressed the diazoxide-induced increases in the outward current and the pretreatment with this agent prevented the development of the diazoxide-induced outward current. 5. Cibenzoline (10 microM) reversed the 2,4-dinitrophenol (50 microM)-induced shortening of the action potential duration partially but significantly. 6. These results suggest that diazoxide activates ATP-sensitive K+ channels of guinea-pig ventricular cells and that cibenzoline, at therapeutic concentrations, inhibits this channel.

Classifying antiarrhythmic actions: by facts or speculation

Classification of antiarrhythmic actions is reviewed in the context of the results of the Cardiac Arrhythmia Suppression Trials, CAST 1 and 2. Six criticisms of the classification recently published (The Sicilian Gambit) are discussed in detail. The alternative classification, when stripped of speculative elements, is shown to be similar to the original classification. Claims that the classification failed to predict the efficacy of antiarrhythmic drugs for the selection of appropriate therapy have been tested by an example. The antiarrhythmic actions of cibenzoline were classified in 1980. A detailed review of confirmatory experiments and clinical trials during the past decade shows that predictions made at the time agree with subsequent results. Classification of the effects drugs actually have on functioning cardiac tissues provides a rational basis for finding the preferred treatment for a particular arrhythmia in accordance with the diagnosis.

Cibenzoline. A review of its pharmacological properties and therapeutic potential in arrhythmias

Cibenzoline is a class I antiarrhythmic drug with limited class III and IV activity which can be administered orally or intravenously. An elimination half-life of about 8 to 12 hours permits twice daily administration, although age and renal function must be considered when determining dosage. Cibenzoline has some activity in ventricular and supraventricular arrhythmias, including drug-refractory ventricular tachycardia or ventricular arrhythmias following recent acute myocardial infarction, although results in patients with sustained ventricular tachycardia are less promising. In comparative trials, cibenzoline has demonstrated efficacy similar to or better than that of a variety of other class I antiarrhythmic drugs and was at least as well tolerated, with a more convenient dosage schedule. However, further studies to clarify the proarrhythmic effects of cibenzoline and its use in patients with impaired left ventricular function are required, and the use of cibenzoline (and other class I antiarrhythmic agents) in patients with other than potentially lethal ventricular arrhythmias should be avoided following the results of the CAST studies. Thus, cibenzoline is an effective antiarrhythmic agent with a favourable pharmacokinetic profile that may be considered with other class I drugs in patients requiring therapy for high risk arrhythmias.

Effect of a novel class I antiarrhythmic agent, TYB-3823, on the calcium current in single guinea pig ventricular myocytes

The effect of TYB-3823 on Ca2+ current (ICa) of guinea pig ventricular myocytes was investigated by means of whole-cell patch-clamp technique. TYB-3823 (100-1,000 microM) caused a concentration-dependent decrease in ICa. Furthermore, a reduction of ICa induced by TYB-3823 (1,000 microM) was progressively accentuated by repetitive membrane depolarization, indicating a rate-dependent block of ICa. However, the inhibitory potency on ICa was approximately 1/1000 of a Ca2+ antagonistic agent, verapamil hydrochloride. Considering evidence that 3-30 microM TYB-3823 decreased the maximum upstroke velocity of the action potential of guinea pig ventricular muscles, it is indicated that the drug does not show its Ca2+ antagonistic property in the usual concentration range as a class I antiarrhythmic agent.

Randomized comparison of flecainide and cibenzoline in the conversion of atrial fibrillation

The efficacy of oral cibenzoline (260 mg/day and 320 mg/day) and flecainide (200 mg/day and 300 mg/day) in the conversion of chronic atrial fibrillation to sinus rhythm were compared in 31 patients in a randomized order. If sinus rhythm was not restored on the 5th day of oral treatment with either cibenzoline or flecainide (phase of initial treatment) patients were switched to a second phase of treatment with the drug not given in the first phase after a washout phase of 3 days. Sinus rhythm was restored in 7/28 treatment trials with cibenzoline and in 7/23 treatment trials with flecainide (not significant). Trough levels of cibenzoline and flecainide in the plasma were not significantly different between patients in whom sinus rhythm was restored and patients with persisting atrial fibrillation. In patients successfully converted to sinus rhythm, long-term treatment was instituted with flecainide (n = 6) or cibenzoline (n = 6). Atrial fibrillation developed in 2 patients in each group of patients within 3 months. In all other patients, sinus rhythm was maintained during the follow-up period of 12 months. Non-cardiac side effects were observed in 2 patients during treatment with cibenzoline and flecainide respectively. With flecainide, one patient developed sinus arrest up to 5.6 seconds.

Comparison of Ca2+ channel inhibitory effects of cibenzoline with verapamil on guinea-pig heart

1. Cibenzoline, a class 1 antiarrhythmic drug, was studied on the effects upon the myocardial slow inward Ca2+ current (ICa) and the contractile force, and was compared with verapamil. 2. In voltage-clamp experiments with guinea-pig ventricular myocytes, cibenzoline caused a concentration-related inhibition of ICa (IC50 = 30 microM), whereas verapamil exerts a stronger effect (IC50 = 0.6 microM). 3. Cibenzoline also produced a concentration-related decrease in contractile force of isolated papillary muscle preparation (IC50 = 30 microM), while IC50 of verapamil was 0.8 microM. 4. Although the myocardial Ca2+ channel blocking effect of cibenzoline is about 1/50 compared to verapamil, cibenzoline possesses an inhibitory action on Ca2+ channel as well as on Na+ channel.

Electrophysiologic effects and efficacy of cibenzoline on stimulation-induced atrial fibrillation and flutter and implications for treatment of paroxysmal atrial fibrillation

The effects of intravenous cibenzoline (1.5 mg/kg) on atrial vulnerability and electrophysiology were assessed in 25 patients with documented paroxysmal atrial fibrillation (AF), in whom sustained (greater than 30 seconds) AF was induced by atrial stimulation with up to 2 extrastimuli and paced rates between 100 and 180 beats/min. In 7 patients AF persisted despite the application of cibenzoline, and in 8 patients the induction of sustained AF was prevented by cibenzoline. Intraatrial conduction time, flutter cycle length and shortest ventricular cycle length during AF were increased by cibenzoline (p less than or equal to 0.01). Sinus cycle length was decreased (p less than or equal to 0.05), whereas sinus node recovery time remained unchanged. The effective refractory period of the right atrium was not significantly affected. Eight patients with frequent episodes of paroxysmal AF received oral cibenzoline for control of paroxysmal AF irrespective of the efficacy of intravenous cibenzoline. Prevention of stimulation-induced AF predicted successful treatment of paroxysmal AF (p = 0.018). Cibenzoline could be effective in the treatment of atrial arrhythmias, and selection of an antiarrhythmic therapy for recurrent AF seems to be useful.

Ro 15-4513: partial inverse agonism at the BZR and interaction with ethanol

The imidazobenzodiazepinone derivative Ro 15-4513 has the activity profile of a partial inverse (low efficacy) agonist at the benzodiazepine receptor (BZR). It reverses central nervous depressant effects of diazepam, and, in part, of phenobarbitone and ethanol in mice, rats and cats in behavioural, electrophysiological, and neurochemical paradigms. The interaction of Ro 15-4513 with barbiturates and ethanol is due to its inverse agonistic (negative allosteric modulatory) property at the BZR, as it was reversed by the selective BZR blocker flumazenil (Ro 15-1788). In the present experiment situations, other BZR partial inverse agonists in subconvulsant or overt convulsant doses were less effective against ethanol effects than Ro 15-4513. Possible mechanisms for this differential activity of BZR inverse agonists are discussed.

Effect of cibenzoline, a class I antiarrhythmic drug, on action potential in canine ventricular muscle

Effect of cibenzoline, a class I (local anesthetic-type) antiarrhythmic drug, was investigated upon canine ventricular muscle using a conventional micro-electrode method. In the presence of cibenzoline at the concentration of 3 X 10(-6) M or higher, the maximum rate of rise of the action potential was inhibited and the action potential duration was lengthened significantly in a concentration-dependent manner. The effective refractory period was also prolonged. From its effect on the action potential duration, cibenzoline should belong to Ia, according to the Vaughan Williams classification of antiarrhythmic agents. On the other hand, cibenzoline inhibition of the maximum rate of depolarization was greater with an increase in stimulation frequency (a use-dependent block). In the presence of cibenzoline concentrations of 3 X 10(-6) M and 8 X 10(-6) M, which blocked the maximum rate of depolarization by 36% and 67% at 180 beats/min, the rates of onset of inhibition of the maximum rate of depolarization were 0.109 +/- 0.027 and 0.146 +/- 0.070 AP-1 (mean +/- S.D.), respectively. From the kinetics of inhibition of the maximum rate of depolarization, these results suggest that cibenzoline should be classified as an intermediate drug with the prolongation of the action potential duration.