Comparison of the electrophysiologic effects of intravenous and oral lorcainide in patients with recurrent ventricular tachycardia

Newer antiarrhythmic drugs

The effective management of cardiac arrhythmias remains a major challenge in cardiovascular therapeutics. The management of arrhythmias encompasses a wide spectrum of supraventricular and ventricular tachyarrhythmias occurring in patients with various cardiac diagnoses and different degrees of myocardial dysfunction. A number of the newer antiarrhythmic drugs that have either recently been released or appear promising are reviewed in this article. Drugs are described with respect to their basic pharmacology, electrophysiologic actions, pharmacokinetics and metabolism, hemodynamics, antiarrhythmic effects, side effects, interactions, indications, and dosage.

Lorcainide for the treatment of refractory ventricular tachycardia: clinical and electrophysiologic results

The electrophysiologic effects and antiarrhythmic efficacy of lorcainide were evaluated using programmed electrical stimulation (PES) in 14 patients with ventricular tachycardia (VT) refractory to conventional drug therapy. Lorcainide was administered orally (200-400 mg/d, eight patients), intravenously (150 mg/d, one patient), or by both routes (250-380 mg/d, five patients) prior to PES. In 13 patients undergoing both control and lorcainide PES, lorcainide increased the QRS duration (102 +/- 28 to 125 +/- 28 ms, P less than .001) and the QTc interval (430 +/- 39 to 471 +/- 32 ms, P less than .01) but had no effect on the RR interval (786 +/- 156 to 780 +/- 172 ms, P greater than .2). The right ventricular effective refractory period increased from 258 +/- 8 to 285 +/- 22 ms (P less than .001). Lorcainide prevented VT induction or resulted in induction of only well-tolerated, nonsustained VT in six of 14 patients (43%). The cycle length of induced VT increased from 264 +/- 32 to 306 +/- 34 ms (P less than .01). Of six patients started on chronic therapy, four still receive lorcainide after 18 +/- 7 months. Adverse effects have consisted mainly of sleep disturbances. Thus, it can be stated that lorcainide is effective in certain patients with VT refractory to conventional therapy.

Comparison in vitro of the electrophysiological effects of lorcainide and its metabolite norlorcainide

The effects of lorcainide and its metabolite norlorcainide on the maximal rate of depolarization (Vmax) were compared at different rates of stimulation and at various membrane potentials in ventricular muscle preparations of guinea-pig heart. A standard microelectrode technique was used. The results show that lorcainide and norlorcainide exerted qualitatively similar effects; they both depressed Vmax in a frequency- and potential-dependent way. The following quantitative differences were found: lorcainide was about 50% more potent in depressing Vmax; this difference in potency was observed at 1 and 2 Hz stimulation rates; the block by lorcainide was clearly potential-dependent; in the case of norlorcainide this effect was weak; the onset and removal of block were about twice as fast with lorcainide; the block per action potential was greater with lorcainide. The electrophysiological effects were decreased in the presence of alpha 1-acid glycoprotein, though to a similar extent with both drugs. Taking into account the difference in potency found in the present experiments and the difference in plasma concentration described in the literature, it is concluded that the parent drug and its metabolite both contribute to about the same extent to the in vivo effect of oral treatment with lorcainide.

Intravenous lorcainide versus lidocaine in the treatment of frequent and complex ventricular arrhythmias

Thirty patients with frequent (greater than or equal to 30/hr) and repetitive ventricular premature beats (VPBs) unassociated with acute infarction were randomized to intravenous lorcainide (LOR) or lidocaine (LID). Following at least 2 hours of baseline Holter monitoring, patients received LOR, 2 mg/kg then 200 mg/24hr, or LID, 1 mg/kg then 2 mg/min, with rebolus if needed. Nonresponders detected by bedside telemetry were crossed over. Clinical response was 6 of 25 (24%) including two of nine crossovers with LOR and 8 of 26 (31%) including 3 of 12 crossovers with LID (p = NS). By computer analysis of 24-hour Holter monitors and asymptotic regression of success rates at hourly intervals, it was projected that greater than or equal to 80% reduction in VPBs occurred in 28% of LOR and in 25% of LID (p = NS), and complete suppression of repetitive VPBs occurred in 102% of LOR and in 92% of LID (p = NS). The mean drug levels were 405 ng/ml (range 371 to 463) with LOR and 3.4 micrograms/ml (range 2.1 to 3.6) with LID. Side effects were similar, occurring in 8 of 25 LOR trials and in 11 of 26 LID trials (p = NS). Thus, LOR and LID effectively suppress repetitive VPBs and to a lesser extent VPB frequency. However, neither drug is superior and each may be an effective alternative when resistance to the other is encountered.

Intravenous and oral lorcainide: assessment of central nervous system toxicity and antiarrhythmic efficacy

Twenty-eight subjects underwent evaluation of drug toxicity and antiarrhythmic efficacy with oral and intravenous lorcainide. Lorcainide, a new type 1C antiarrhythmic drug, has an active metabolite, norlorcainide, which accumulates after oral but not significantly after intravenous administration. Group 1 consisted of 14 subjects who received intravenous lorcainide with an initial bolus of 2 mg/kg at a rate of 2 mg/min followed by 0.14 mg/min or 200 mg/24 hours. The lorcainide level after bolus was 0.432 micrograms/ml and fell to 0.178 micrograms/ml at 4 to 6 hours despite constant drug infusion. Prior work has demonstrated no detectable norlorcainide levels after intravenous infusion. Group II consisted of 14 subjects who received oral lorcainide, 100 mg orally every 8 hours. Mean lorcainide levels were 0.287 micrograms/ml and mean norlorcainide levels were 0.377 micrograms/ml. Only 2 of 12 subjects in group I experienced headache, dizziness, or sleep disturbance, compared to 12 of 14 subjects in group II (p less than 0.01). Intravenous lorcainide has a lower incidence of central nervous system side effects than oral lorcainide. These effects may be attributable to the accumulation of the norlorcainide metabolite with oral therapy.

Chronic lorcainide therapy for symptomatic premature ventricular complexes: efficacy, pharmacokinetics and evidence for norlorcainide antiarrhythmic effect

Chronic premature ventricular complexes (PVCs) have been effectively suppressed by oral lorcainide as reported in previous short-term studies. The plasma level-effect relation of lorcainide may be affected by the possible cardioactivity of norlorcainide, a metabolite that accumulates after repeated oral doses. This study evaluated the long-term efficacy of lorcainide in suppressing chronic symptomatic PVCs, and examined the relation of arrhythmia suppression to plasma concentrations of lorcainide and norlorcainide. Fourteen patients were treated with lorcainide, 200 to 400 mg/day, 12 of whom achieved nearly complete suppression of arrhythmias after treatment for 1 year. Chronic lorcainide treatment was well tolerated; no patient discontinued treatment because of adverse effects. Lorcainide and norlorcainide plasma concentrations remained stable after the first week of therapy. Antiarrhythmic activity persisted throughout the year. Upon drug withdrawal, the mean lorcainide washout half-life was 14.3 +/- 3.7 hours and the mean norlorcainide washout half-life was 31.9 +/- 8.9 hours. The return of arrhythmias occurred well after the lorcainide plasma concentration had decreased to subtherapeutic levels, suggesting an antiarrhythmic effect of norlorcainide. Thus, long-term lorcainide therapy is effective in treating chronic symptomatic PVCs and is well tolerated by most patients. The metabolite norlorcainide appears to have antiarrhythmic activity independent of lorcainide.

Treatment with oral lorcainide in patients with sustained ventricular tachycardia and fibrillation

Fifty patients with drug-refractory (failed 7 +/- 2 other drug trials) sustained ventricular tachycardia or fibrillation were treated with oral lorcainide. Twenty-three patients underwent programmed stimulation both before and after oral lorcainide, and all 23 remained inducible, although ventricular tachycardia cycle length was prolonged and mean arterial pressure was higher. Lorcainide was discontinued in 23 patients prior to hospital discharge because of death in four patients, side effects in five patients, spontaneous clinical arrhythmia recurrence in six patients, and ventricular tachyarrhythmias induced at electrophysiologic study in eight patients. Twenty-seven patients were discharged on an average dose of 169 +/- 56 mg twice a day, including 15 in whom ventricular tachycardia remained inducible. During long-term follow-up the drug was discontinued in 15 patients; three because of side effects, three because of clinical nonfatal arrhythmia recurrence, two who selected other alternative therapy, and seven patients who died suddenly due to ventricular tachyarrhythmias. Twelve patients remain on long-term lorcainide. The actuarial 1-year chance of being arrhythmia free was 38.9%, and 1-year cardiovascular and arrhythmia survival rates were 56.8% and 60.4%, respectively. Based on our data we conclude that: In this extremely drug-resistant patient population the clinical efficacy of lorcainide is low; lorcainide should not be used empirically in such highly drug-resistant patients; persistent ventricular tachyarrhythmia inducibility at electrophysiologic study implies a poor prognosis in patients treated with oral lorcainide; the incidence of becoming noninducible during oral lorcainide therapy in highly drug-resistant patients appears low; and for patients in whom the drug seems partially beneficial it could be used in conjunction with a backup automatic implantable cardioverter/defibrillator.

Metabolites of cardiac antiarrhythmic drugs: their clinical role

Most antiarrhythmic drugs are extensively metabolized, and the accumulation of the metabolites of several of these drugs has been documented. In some cases, the steady-state plasma concentrations of metabolites are considerably greater than is the concentration of the parent drug. Several of these metabolites have been evaluated in animal models for antiarrhythmic activity and their potencies have been defined relative to the activity of their parent compound. Evaluations of activity are generally conducted in animal arrhythmia models, and very few metabolites of antiarrhythmic drugs have been evaluated directly in patients. However, from knowledge of antiarrhythmic activity in animals and the degree to which a metabolite accumulates in the plasma of patients, one can make qualitative judgments about its therapeutic role. Such judgments, however, need to be recognized as tenuous. Quantitative judgments require further information regarding the relationship between the parent drug and metabolite when present simultaneously in the myocardium. One must consider whether the effects of the parent drug and metabolite are additive, synergistic, or even antagonistic. The latter case is most possible with drug-metabolite pairs where the metabolite accumulates substantially, but does not have significant antiarrhythmic potency. Other considerations include noncardiac effects of the metabolites. As in the case of the mono-desethyl metabolite of lidocaine, the significance of its accumulation relates more to central nervous system side effects than to direct cardiac actions. The role of active metabolites also much be considered in regard to differences in the disposition kinetics between the parent drug and metabolite. The most obvious situation where this is important is in designing clinical drug evaluation protocols. As illustrated by the metabolites of encainide and lorcainide, the time course of accumulation and disappearance of the metabolites may be much longer than that of the parent drug. Clinical evaluations at steady state must take into account the time required to achieve steady-state concentrations of the metabolites as well. Similarly, after discontinuation of drug administration, the time required before washout is complete may be totally dependent on the kinetics of the metabolite, and not the parent drug. Variability in metabolic activity also needs to be considered. It has been shown with procainamide and encainide that genetic factors can influence the rate of production of active metabolites and consequently influence the clinical efficacy of these drugs. Another consideration that deserves attention is the question of drug interactions.(ABSTRACT TRUNCATED AT 400 WORDS)

Hyponatremia in patients treated with lorcainide, a new antiarrhythmic drug

The effects of lorcainide, a new antiarrhythmic drug, on serum electrolytes and osmolality are described in a series of 33 patients with organic heart disease and complex ventricular arrhythmias treated with lorcainide. In eight patients, a mean decrease in serum Na+ of 8.25 +/- 3.2 mEq/L was observed after a single 200 mg intravenous dose of lorcainide. Sixteen of 33 patients developed significant hyponatremia and hypoosmolality during oral treatment with lorcainide. In all except two patients, serum Na+ returned to normal values within 3 to 12 months of continued lorcainide therapy. Low serum Na+ and hypoosmolality in the absence of volume depletion, clinically manifest edema, and unaltered renal, adrenal, cardiac, or thyroid function suggest that this antiarrhythmic drug produced the syndrome of inappropriate antidiuretic hormone secretion (SIADH). SIADH appeared to be transient and asymptomatic in our patients. One patient developed severe hyponatremia with serum Na+ of 108 mEq/L when hydrochlorothiazide was given to control hypertension. It is concluded that SIADH is an important side effect of lorcainide therapy. We recommend that serum Na+ be carefully monitored in patients started on lorcainide therapy, and extreme caution should be exercised in prescribing diuretics to patients with persistent hyponatremia.

Clinical pharmacokinetics of the newer antiarrhythmic agents

This article reviews clinical pharmacokinetic data on 8 new antiarrhythmic agents. Some of these drugs have been studied extensively while others are relatively new, with incomplete data due to limited evaluation. Amiodarone is a class III antiarrhythmic drug which is effective in treating many atrial and ventricular arrhythmias that are refractory to other drugs. Amiodarone accumulates extensively in tissues and its disposition characteristics are best described by models with 3 and 4 compartments. Its apparent volume of distribution is very large (1300 to 11,000L) and its elimination half-life very long (53 days). A delay of up to 28 days from of treatment to onset of antiarrhythmic effect may be observed, and the antiarrhythmic effect may persist for weeks to months following cessation of therapy. Clinically significant drug interactions have been observed with amiodarone and warfarin, digoxin, quinidine and procainamide. Encainide is a class Ic antiarrhythmic drug. Although it has a short elimination half-life (1 to 3h), 2 major metabolites with antiarrhythmic effects accumulate in the plasma of patients during long term therapy. Plasma concentrations of O-demethyl encainide appear to correlate with the antiarrhythmic effect. Flecainide, another class Ic antiarrhythmic agent, has an elimination half-life of 14 hours which makes it suitable for twice daily dosing. Flecainide elimination is prolonged in patients with low output heart failure. Significant drug interactions with digoxin and cimetidine have been reported. Lorcainide is also a class Ic antiarrhythmic drug, the bioavailability of which is nonlinear. Clearance of the drug is reduced during long term therapy. A major active metabolite, norlorcainide, accumulates in the plasma of patients during long term therapy and its concentration exceeds that of lorcainide by a factor of 2. The elimination half-lives of lorcainide (9h) and norlorcainide (28h) allow for once or twice daily dosing. Mexiletine, a class Ib antiarrhythmic drug, is structurally similar to lignocaine (lidocaine). A sustained release formulation provides effective plasma concentrations when administered twice daily. The apparent volume of distribution of mexiletine is 5.0 to 6.6 L/kg, and the elimination half-life varies from 6 to 12 hours in normal subjects and from 11 to 17 hours in cardiac patients. Mexilitine is extensively metabolised but the metabolites are not pharmacologically active. Renal elimination of mexiletine is pH dependent. Drugs which induce hepatic metabolism significantly alter the pharmacokinetics of mexiletine.(ABSTRACT TRUNCATED AT 400 WORDS)

Therapy with investigational antiarrhythmic drugs

The investigational antiarrhythmic agents available for use in this country are predominantly class I drugs with local anesthetic membrane effects. These drugs are often used successfully to control arrhythmias refractory to treatment with the standard antiarrhythmic drugs. Side effects often limit their use, and particular attention needs to be paid to their cardiac side effects, such as exacerbation of arrhythmia or enhanced conduction defects.

Pharmacology of lorcainide

Lorcainide is a new type 1 antiarrhythmic drug that is well absorbed orally, with bioavailability increasing with both dose and continued administration. It is metabolized through the liver, and patients with significant liver disease will require dosage reduction. The drug has an active metabolite, norlorcainide, whose activity is similar to that of lorcainide but whose half-life is 26 hours instead of 8 for the parent compound. The levels of this metabolite are nearly twice those of lorcainide at steady state. The long half-life of the metabolite and the changing bioavailability of lorcainide require that a given dose be administered for 1 week for the maximum effect to be demonstrated.

Antiarrhythmic therapy: clinical pharmacology update

Currently available antiarrhythmic agents are limited by side effects and the potential for increasing arrhythmias. In addition, drug interactions, altered disposition of drug as a result of changes in protein binding or concomitant disease processes, active metabolites, and poorly defined therapeutic ranges with great interpatient variability are some of the factors which complicate therapy. An awareness of the possible contribution of these factors in the use of antiarrhythmics is invaluable in both the choice of agent and the establishment of an optimum benefit-to-risk ratio for the patient.

Clinical efficacy and electrophysiology of oral propafenone for ventricular tachycardia

Sixteen patients with ventricular tachycardia (VT) or nonfatal cardiac arrest were treated with propafenone (P), 900 mg/day. Electrophysiologic studies were performed before and during therapy with P. All patients had inducible sustained VT at the baseline study. During P therapy, VT was not inducible in 1 patient, was unsustained in 1 and was harder to induce in 2 patients. P increased the cycle length of VT from 307 +/- 67 to 382 +/- 107 ms. Five patients began outpatient therapy with P, including 2 in whom VT was slowed to less than 125 beats/min. Two are arrhythmia-free during follow-up of 2 and 8 months. P significantly increased intraatrial conduction time (from 44 +/- 12 to 72 +/- 22 ms), AH interval (from 115 +/- 36 to 152 +/- 45 ms), HV interval (from 55 +/- 18 to 92 +/- 42 ms), QRS duration (from 140 +/- 36 to 180 +/- 48 ms) and QT interval (from 402 +/- 30 to 459 +/- 60 ms). P increased atrial (from 247 +/- 36 to 288 +/- 38 ms) and ventricular (from 249 +/- 20 to 277 +/- 32 ms) effective refractory periods, Sinus cycle length did not change, but the corrected sinus node recovery time increased (from 162 +/- 85 to 821 +/- 1,607 ms). P aggravated arrhythmias in 4 patients. The plasma P concentration, measured either at the time of electrophysiologic studies of when therapy was discontinued, was 753 +/- 428 ng/ml. P suppressed ventricular ectopic beats in 33% and increased them in 1 patient. P has antiarrhythmic activity against VT similar to that of other antiarrhythmic drugs and has potential for serious adverse effects in some patients.