Acute effects of antiarrhythmic drugs on stable ventricular premature beats. Controlled comparison of lorcainide and lidocaine

Comparative pharmacodynamics of intravenous lidocaine in patients with acute and chronic ventricular arrhythmias

OBJECTIVE

To evaluate the pharmacodynamics of intravenous lidocaine in patients with acute-onset and chronic ventricular arrhythmias.

DESIGN

Open-label, pharmacodynamic evaluation.

SETTING

Private, university-affiliated, hospital coronary-care unit.

PATIENTS

Twenty cardiac patients with acute-onset ventricular ectopy and 20 with chronic ventricular ectopy.

INTERVENTIONS

Intravenous lidocaine was administered to all patients as a 1-mg/kg bolus, a 0.5-mg/kg bolus, and a 2.8-mg/min constant infusion for 48 hours.

MAIN OUTCOME MEASURES

Changes in ventricular premature beat (VPB) frequency against total treatment period frequency and by an hour-to-hour assessment of changes in VPB frequency compared with total baseline frequencies. Response was defined as greater than or equal to 80 percent total VPB reduction, greater than or equal to 90 percent paired VPB reduction, and total abolition of nonsustained ventricular tachycardia events.

RESULTS

A statistically significant difference in the pharmacodynamic effects of lidocaine were observed during the first eight hours of treatment in patients with acute-onset and chronic VPBs. The number of patients with acute-onset VPBs who responded to lidocaine in the first hour of treatment did not change significantly over the remaining hours of treatment. Response to lidocaine was less in patients with chronic VPBs than in patients with acute-onset VPBs. The response rate to lidocaine was significantly less during the first eight hours in patients with chronic VPBs than in patients with acute-onset VPBs. Following eight hours of treatment, the response rates between acute-onset and chronic VPB patients were not significantly different. Mean lidocaine plasma concentrations were not different between the groups. In addition, there were no significant differences in the incidence of adverse effects between the two groups.

CONCLUSIONS

The onset of antiarrhythmic effect as measured by suppression of ventricular ectopy is delayed in patients with chronic VPBs compared with patients with acute-onset VPBs. Decisions about lidocaine response in patients with chronic VPBs cannot be made accurately in the first eight hours of therapy.

Pharmacokinetic implications of lorcainide therapy in patients with normal and depressed cardiac function

The influence of cardiac function as measured by the left ventricular ejection fraction on the pharmacokinetic variables of a new antiarrhythmic drug, lorcainide, was investigated in 20 cardiac patients. Patients were divided into two groups: those with normal (ejection fraction greater than .40) or depressed (ejection fraction less than .40) left ventricular function. The elimination half-life, plasma clearance rates, or volume of distribution of lorcainide were not significantly different in patients with either normal or depressed cardiac function. A decrease in arrhythmia frequency could be correlated to plasma lorcainide concentration in the majority of patients, and it was noted that at least 0.1 mg/L of lorcainide was required for the presence of an antiarrhythmic effect. Three unusual cases are presented to illustrate the importance of measuring plasma drug concentrations and calculating the drug pharmacokinetics and to correlate these to the antiarrhythmic response in order to minimize the risk of plasma drug accumulation and side effects. A review of published data shows a three- to sixfold interpatient variation in the elimination half-life of lorcainide with practical implications in its use as an antiarrhythmic drug.