Pilsicainide

Characterization of remodeling processes in the atria of atrioventricular block dogs: Utility as an early-stage atrial fibrillation model

To characterize utility of atrioventricular block (AVB) dogs as atrial fibrillation (AF) model, we studied remodeling processes occurring in their atria in acute (<2 weeks) and chronic (>4 weeks) phases. Fifty beagle dogs were used. Holter electrocardiogram demonstrated that paroxysmal AF occurred immediately after the production of AVB, of which duration tended to be prolonged in chronic phase. Electrophysiological analysis showed that inter-atrial conduction time and duration of burst pacing-induced AF increased in the chronic phase compared with those in the acute phase, but that atrial effective refractory period was hardly altered. Echocardiographic study revealed that diameters of left atrium, right pulmonary vein and inferior vena cava increased similarly in the acute and chronic phases. Histological evaluation indicated that hypertrophy and fibrosis in atrial tissue increased in the chronic phase. Electropharmacological characterization showed that i.v. pilsicainide effectively suppressed burst pacing-induced AF with increasing atrial conduction time and refractoriness of AVB dogs in chronic phase, but that i.v. amiodarone did not exert such electrophysiological effects. Taken together, AVB dogs in chronic phase appear to possess such pathophysiology as developed in the atria of early-stage AF patients, and therefore they can be used to evaluate drug candidates against early-stage AF.

Case report: An autopsy case of pilsicainide poisoning

We present a fatal case of pilsicainide poisoning. Quantitative toxicological analysis revealed that the concentrations of pilsicainide in femoral blood and urine samples were 17.5 μg/mL and 136.9 μg/mL, respectively. No morphological changes due to poisoning were observed. Based on the autopsy findings, results of the toxicological examination, and investigation by the authorities, we concluded that the cause of death was due to pilsicainide poisoning.

Translational Studies on Anti-Atrial Fibrillatory Action of Oseltamivir by its in vivo and in vitro Electropharmacological Analyses

Oseltamivir has been shown to prolong the atrial conduction time and effective refractory period, and to suppress the onset of burst pacing-induced atrial fibrillation in vitro. To better predict its potential clinical benefit as an anti-atrial fibrillatory drug, we performed translational studies by assessing in vivo anti-atrial fibrillatory effect along with in vivo and in vitro electropharmacological analyses. Oseltamivir in intravenous doses of 3 (n = 6) and 30 mg/kg (n = 7) was administered in conscious state to the persistent atrial fibrillation model dogs to confirm its anti-atrial fibrillatory action. The model was prepared by tachypacing to the atria of chronic atrioventricular block dogs for > 6 weeks. Next, oseltamivir in doses of 0.3, 3 and 30 mg/kg was intravenously administered to the halothane-anesthetized intact dogs to analyze its in vivo electrophysiological actions (n = 4). Finally, its in vitro effects of 10–1,000 μM on I_K,ACh, I_Kur, I_Kr, I_Na and I_CaL were analyzed by using cell lines stably expressing Kir3.1/3.4, K_V1.5, hERG, Na_V1.5 or Ca_V1.2, respectively (n = 3 for I_K,ACh and I_Kr or n = 6 for I_Kr, I_Na and I_CaL). Oseltamivir in doses of 3 and 30 mg/kg terminated the atrial fibrillation in 1 out of 6 and in 6 out of 7 atrial fibrillation model dogs, respectively without inducing any lethal ventricular arrhythmia. Its 3 and 30 mg/kg delayed inter-atrial conduction in a frequency-dependent manner, whereas they prolonged atrial effective refractory period in a reverse frequency-dependent manner in the intact dogs. The current assay indicated that IC₅₀ values for I_K,ACh and I_Kr were 160 and 231 μM, respectively, but 1,000 µM inhibited I_Na, I_CaL and I_Kur by 22, 19 and 13%, respectively. The extent of I_Na blockade was enhanced at faster beating rate and more depolarized resting membrane potential. Oseltamivir effectively terminated the persistent atrial fibrillation, which may be largely due to the prolongation of the atrial effective refractory period and inter-atrial conduction time induced by I_K,ACh and I_Kr inhibitions along with I_Na suppression. Thus, oseltamivir can exert a powerful anti-atrial fibrillatory action through its ideal multi-channel blocking property; and oseltamivir would become a promising seed compound for developing efficacious and safe anti-atrial fibrillatory drugs.

Synergistic Effect of Dofetilide and Mexiletine on Prevention of Atrial Fibrillation

Background

Although atrial fibrillation (AF) is the most common abnormal heart rhythm and its prevalence continues to rise, there is a marked paucity of effective and safe antiarrhythmic drugs for AF. This study was done to test whether combined use of dofetilide and mexiletine exhibits not only a synergistic effect on AF suppression but also a safer profile in drug‐induced ventricular proarrhythmias.

Methods and Results

The effects of dofetilide plus mexiletine on atrial effective refractory period (ERP), AF inducibility, QT, and QT‐related ventricular arrhythmias were studied using the isolated arterially perfused rabbit atrial and ventricular wedge preparations. Dofetilide or mexiletine alone mildly to moderately prolonged atrial ERP, but their combined use produced a markedly rate‐dependent increase in atrial ERP. Dofetilide (3 nmol/L) plus mexiletine (10 μmol/L) increased the ERP by 28.2% from 72.2±5.7 to 92.8±5.9 ms (n=9, P<0.01) at a pacing rate of 0.5 Hz and by 94.5% from 91.7±5.2 to 178.3±12.0 ms (n=9, P<0.01) at 3.3 Hz. Dofetilide plus mexiletine strongly suppressed AF inducibility. On the other hand, dofetilide at 10 nmol/L produced marked QT and T_p‐e prolongation, steeper QT‐BCL and T_p‐e‐BCL slopes, and induced early afterdepolarizations and torsade de pointes in the ventricular wedges. Mexiletine at 10 μmol/L reduced dofetilide‐induced QT and T_p‐e prolongation, QT‐BCL and T_p‐e‐BCL slopes, and abolished early afterdepolarizations and torsade de pointes.

Conclusions

In rabbits, combined use of dofetilide and mexiletine not only synergistically increases atrial ERP and effectively suppresses AF inducibility, but also markedly reduces QT liability and torsade de pointes risk posed by dofetilide alone.

Paroxysmal atrial fibrillation recurrences and quality of life in symptomatic patients: A crossover study of flecainide and pilsicainide

Background

The therapeutic goals of atrial fibrillation (AF) patients are to reduce symptoms and prevent severe complications associated with AF. This study compared the efficacy of flecainide versus pilsicainide in reducing the frequency of AF and improving quality of life (QOL) in symptomatic paroxysmal AF patients without structural heart disease.

Methods

The Atrial Fibrillation and Quality Of Life (AF-QOL) study was a prospective, multicenter, randomized, open-label crossover study that compared flecainide and pilsicainide as antiarrhythmic drug therapy. Patients were randomized to receive 3 months of treatment with flecainide twice daily or pilsicainide 3 times daily. Each treatment consisted of a dose-finding phase (weeks 1–4) and an efficacy phase (weeks 5–12). Forty-three patients completed the trial. The main outcome was the number of days with documented AF episodes using a patient-operated electrocardiogram. QOL questionnaires (SF-36 and AF-specific QOL scores) were also completed.

Results

The median (range) AF frequencies (days/8 weeks) were 2 (0–50) in the flecainide treatment group and 1 (0–54) in the pilsicainide treatment group (no significant between-group difference). No significant difference in the first recurrence of AF during the efficacy phase was noted between flecainide and pilsicainide treatments. The frequency and severity scores of AF-related symptoms improved from baseline to the end of the treatment periods. No significant differences in SF-36 or AF-related QOL scores were noted between the treatment groups.

Conclusions

This study found no difference in AF frequency or QOL between symptomatic paroxysmal AF patients who received flecainide or pilsicainide.

Assessment of drug-induced proarrhythmias due to pilsicainide in patients with atrial tachyarrhythmias

Background

Pilsicainide, a pure Na⁺ channel blocker, is a popular antiarrhythmic drug for the management of atrial tachyarrhythmias (AT), in Japan. However, serious drug-induced proarrhythmias (DIPs) may unexpectedly occur. We assessed the clinical background of AT patients presenting with DIPs caused by pilsicainide.

Methods

This study retrospectively enrolled 874 consecutive patients (543 men, 63.6±15.3 years old, and 57.9±16.5 kg of body weight), who were orally administered pilsicainide for AT management. We evaluated the relationship between DIPs and serum pilsicainide concentration, renal dysfunction (estimate glomerular filtration rate, eGFR), and electrocardiogram (ECG) parameters.

Results

Among the patients, 154 (17.6%) had renal dysfunction (eGFR<50 mL/min), including 12 (1.4%) on hemodialysis. DIPs were present in 10 patients (1.1%): all had renal dysfunction, and one was on hemodialysis. The eGFR in DIP patients was significantly lower than that in the non-DIP patients (32.2±15.1 vs. 68.4±22.1 mL/min, p<0.001). Among the clinical factors measured, only renal dysfunction (eGFR<50 mL/min) was significantly associated with DIPs (OR 44.6; 95% CI 5.61–335.0, p<0.001). Interestingly, among the ECG parameters, the corrected QT (QTc) intervals in DIP patients were longer than those in non-DIP patients (555.8±37.6 vs. 430.7±32.6 ms, p<0.001). As pilsicainide concentration increased, both QRS and QTc intervals prolonged. The latter were improved by discontinuing pilsicainide administration, and additional treatments.

Conclusions

DIPs caused by pilsicainide administration were strongly associated with renal dysfunction. Hence, confirmation of renal function would be necessary prior to and/or during the pilsicainide administration.