Therapeutic drug monitoring of antiarrhythmic agents

Evaluating the Lidocaine's Initial Dosing in Patients With Ventricular Arrhythmias and Heart Failure Admitted in Intensive Care Units

INTRODUCTION

Lidocaine is an antiarrhythmic with narrow therapeutic window indicated for refractory ventricular arrhythmia. Limited guidance is available regarding the initial infusion rate ranging from 1 to 4 mg/min in patients with heart failure (HF).

OBJECTIVES

The primary objective was to assess the optimal initial dosing of lidocaine therapy in patients with HF and ventricular arrhythmia.

METHODS

The retrospective cohort study was performed to include patients aged 18 years or older with past medical history of HF or new onset HF who developed ventricular arrythmia requiring lidocaine therapy in cardiovascular intensive care units. The primary outcome was lidocaine levels within the therapeutic ranges (defined as 1.5 to 5.0 μg/L). The study also described the predictive performance of lidocaine one compartment PK model using correlation efficient between the population PK model-predicted levels and observed levels.

RESULTS

A total of 56 patients with HF and ventricular arrhythmia was included. The mean lidocaine maintenance dose was 1.1 ± 0.5 mg/min. The median (IQR) lidocaine level was 3.1 (2.3, 4.1) μg/L. The probabilities within therapeutic, supratherapeutic, and subtherapeutic ranges were 66.1%, 19.6%, and 14.3%, respectively in the whole cohort. Predicted lidocaine levels with one compartment PK model were not correlated with observed lidocaine levels (R2 = 0.34). The simulation investigation showed that 1 mg/min rate achieved the highest probability within therapeutic range compared to 0.5, 1.5, and 2.0 mg/min rates (78.6 vs. 53.6, 53.6, and 28.6%, respectively).

CONCLUSION

Lidocaine initial infusion rate should be up to 1 mg/min in patients with HF and ventricular arrhythmia.

Therapeutic drug monitoring of antiarrhythmic drugs

Most antiarrhythmic drugs fulfil the formal requirements for rational use of therapeutic drug monitoring, as they show highly variable plasma concentration profiles at a given dose and a direct concentration-effect relationship. Therapeutic ranges for antiarrhythmic drugs are, however, often very poorly defined. Effective drug concentrations are based on small studies or studies not designed to establish a therapeutic range, with varying dosage regimens and unstandardised sampling procedures. There are large numbers of nonresponders and considerable overlap between therapeutic and toxic concentrations. Furthermore, no study has ever shown that therapeutic drug monitoring makes a significant difference in clinical outcome. Therapeutic concentration ranges for antiarrhythmic drugs as they exist today can give an overall impression about the drug concentrations required in the majority of patients. They may also be helpful for dosage adjustment in patients with renal or hepatic failure or in patients with possible toxicological or compliance problems. Their use in optimising individual antiarrhythmic therapy, however, is very limited.

Human alpha-1-glycoprotein and its interactions with drugs

For about half a century, the binding of drugs to plasma albumin, the "silent receptor," has been recognized as one of the major determinants of drug action, distribution, and disposition. In the last decade, the binding of drugs, especially but not exclusively basic entities, to another plasma protein, alpha 1-acid glycoprotein (AAG), has increasingly become important in this regard. The present review points out that hundreds of drugs with diverse structures bind to this glycoprotein. Although plasma concentration of AAG is much lower than that of albumin, AAG can become the major drug binding macromolecule in plasma with significant clinical implications. Also, briefly reviewed are the physiological, pathological, and genetic factors that influence binding, the role of AAG in drug-drug interactions, especially the displacement of drugs and endogenous substances from AAG binding sites, and pharmacokinetic and clinical consequences of such interactions. It can be predicted that in the future, rapid automatic methods to measure binding to albumin and/or AAG will routinely be used in drug development and in clinical practice to predict and/or guide therapy.

Lidocaine attenuates the hypotensive and inflammatory responses to endotoxemia in rabbits

OBJECTIVE

To assess the effects of lidocaine on the hemodynamic and inflammatory responses to Escherichia coli endotoxemia in rabbits.

DESIGN

Prospective, randomized, controlled experimental study.

SETTING

University laboratory.

SUBJECTS

Twenty-seven female Japanese rabbits, anesthetized with urethane and ventilated mechanically.

INTERVENTIONS

Animals were randomly assigned to one of three groups: a) endotoxemic control group (n = 9), receiving intravenous Escherichia coli endotoxin (0.5 mg/kg bolus) via the mesenteric vein; b) laparotomy control group (n = 9), treated identically to the endotoxemic control group, except for substitution of 0.9% saline for endotoxin; and c) lidocaine-treated group (n = 9), treated identically to the endotoxemic controls and additionally, intravenous lidocaine (3 mg/kg bolus, followed by infusion at 2 mg/kg/hr) was administered immediately after endotoxin

MEASUREMENTS AND MAIN RESULTS

We compared hemodynamics, blood gases, and microscopic findings of lung tissue obtained at necropsy in each group. Laparotomy alone had a minimal effect on the parameters and findings. Endotoxin injection decreased mean systolic arterial pressure from 135 +/- 6 (SD) to 95 +/- 25 mm Hg (p < .05) and increased the mean base deficit from -1.2 +/- 1.8 to -14.4 +/- 4.2 mmol/L (p < .05), and caused the infiltration of neutrophils into the lungs. Lidocaine administration abolished the hypotension and attenuated the increase the base deficit to -9.5 +/- 2.1 mmol/L (p < .05) and the cellular infiltration in comparison with endotoxemic controls.

CONCLUSIONS

Lidocaine attenuated the hemodynamic and inflammatory responses to endotoxemia in rabbits. Findings suggest that lidocaine administration may prevent the development of hypotension and metabolic acidosis during endotoxemia.

Lidocaine attenuates hyperoxic lung injury in rabbits

BACKGROUND

High concentrations of oxygen acute lung injury. Neutrophils are thought to play a pivotal role in the pathogenesis of this lung injury through the release of oxygen radicals, neutral proteases, and lysosomal enzymes. Lidocaine has been shown to inhibit neutrophil function. We examined whether intravenous pretreatment with lidocaine attenuated acute lung injury induced by hyperoxia.

METHOD

Twenty-seven anaesthetized male rabbits were allocated to receive one of three treatments (n = 9 for each group): ventilation with 100% oxygen for 36 h with and without lidocaine treatment, and ventilation with air for 36 h without lidocaine. In the lidocaine-treated group, a single intravenous lidocaine 2 mg/kg was administered immediately after the initiation of exposure to 100% oxygen; thereafter, the lidocaine was infused at a rate of 2 mg.kg(-1).h(-1) for 36 h until the animals were sacrificed. Haemodynamics, PaO2, and lung mechanics were recorded during the ventilation period. After exposure, the lung mechanics and cell fraction in bronchoalveolar lavage fluid (BALF) were measured and analyzed, as was the concentration of activated complements, and cytokines in BALF. The lung wet-to dry- (W/D) weight ratio and albumin concentrations in BALF were analyzed as an index of pulmonary oedema. We also compared the chemiluminescence of neutrophils isolated from the pulmonary artery, and light microscopic findings, in the three groups.

RESULTS

Pure oxygen for 36 h caused no significant changes in haemodynamics, lung mechanics, or PaO2/FiO2 ratio. However, hyperoxia significantly increased the lung W/D weight ratio, the influx of neutrophils into the lung, and BALF concentrations of C3a, C5a, TNF-alpha, IL-1 beta, and albumin. Lidocaine attenuated these increases (W/D ratio: 5.7 vs 5.1, %PMN: 19.2% vs 1.6%, C3a: 62 ng/dl vs 14 ng/dl, C5a: 7.9 ng/dl vs 4.1 nd/dl, TNF-alpha: 25 fmol/ml vs 2.8 fmol/ml, IL-1 beta: 36 fmol/ml vs 2.2 fmol/ml, and albumin: 9.5 mg/dl vs 2.8 mg/dl, all: P < 0.05). The chemiluminescence was increased in hyperoxic compared with in normoxic rabbits and lidocaine treatment attenuated the increase (opsonized zymosan stiluated: 3.7 x 10(6) cpm vs 2.3 x 10(6) cpm, P < 0.05). Exposure to 100% oxygen caused extensive morphologic lung damage which was lessened by lidocaine (lung injury score (mean): 3 vs 4, P < 0.05).

CONCLUSION

These findings suggest that intravenous lidocaine has a prophylactic effect on initial hyperoxic lung injury (pulmonary vascular permeability, histopathological, and biochemical BALF changes) in rabbits. The effects of lidocaine on more severe lung injury (decreased oxygenation) caused by hyperoxia for 72 h deserve further study.

An interindividual variability in the sensitivity of atrioventricular node to diltiazem in patients with paroxysmal supraventricular tachycardia

To study the sensitivity of atrioventricular (AV) node to diltiazem in seven patients with paroxysmal supraventricular tachycardia (PSVT), we analyzed the plasma concentration-response relationship of this Ca-antagonist using AH interval as an index for assessing its Ca channel blocking effect on the AV node after an IV infusion (0.4 mg/kg). The postdose AH intervals were prolonged compared with the baseline, and their percentage changes correlated significantly (P less than 0.01) with log-diltiazem concentrations in all patients. However, drug concentrations associated with a 20% prolongation of AH interval differed considerably among the patients (range; 65 to 260 ng/ml), indicating a large interindividual variability in the sensitivity of AV node to diltiazem. These results suggest that the interindividual difference in the responsiveness of AV node to diltiazem-induced Ca channel blocking effect may be one of the possible explanations for the therapeutic failure of this Ca-antagonist for terminating PSVT or preventing its recurrences in certain patients.

Immediate quantitation of antiarrhythmic drug effect by monophasic action potential recording in coronary artery disease

A contact electrode catheter, which permits clinical recording of cardiac monophasic action potentials (MAPs), was used as a means of quantifying the electrophysiologic effect of 2 antiarrhythmic drugs, procainamide and quinidine. MAP recordings were made in continuous fashion from the right ventricle in 16 patients, before and after the intravenous administration of procainamide (11 patients) or quinidine (5). Increases in the MAP duration at 90% repolarization (MAPD90) were used as indexes of drug effect and related to plasma drug level. Surface electrocardiographic (QRS duration, corrected QT interval [QTC]) and electrophysiologic (ventricular effective refractory period) measurements, in addition to MAPD90, were made at the same time as blood sampling for plasma drug level determination. Dose response curves, plotting change in MAPD90 versus plasma drug level, showed strong linear correlation for both procainamide (p less than 0.0001) and quinidine (p less than 0.0001). The variance (error of estimation) of the predictive relation, change in MAPD90 versus plasma drug level, was significantly lower than that of change in QTC (p less than 0.001), QRS duration (p less than 0.0001) or ventricular effective refractory period (p less than 0.0001) versus plasma drug level for both procainamide and quinidine. Changes in MAP duration closely correlate with plasma drug level, and as such, may serve as an immediate, quantitative indicator of myocardial drug effect during the administration of antiarrhythmic agents.

Overview of the clinical pharmacology of antiarrhythmic drugs

Antiarrhythmic drugs have been recognized to possess 1 or more classes of antiarrhythmic action. This classification scheme is useful, but has major limitations because the available drugs and their metabolites have multiple actions. This report presents an overview of the distinguishing features of the most frequently used agents having class I or III actions. Agents with class I actions are local anesthetic agents that depress the fast inward depolarizing sodium current and thereby slow the rate of the rise of the action potential (phase 0). This category is further divided into classes IA, IB, and IC according to the degree of potency as sodium channel inhibitors, and the individual effects of the drug on action potential, conduction velocity and repolarization. Included in the spectrum of agents with class I action are quinidine, procainamide, disopyramide, lidocaine, tocainide, mexiletine, flecainide, amiodarone, encainide and lorcainide. The antiarrhythmic drugs that exert class III action lengthen repolarization and refractoriness; included in this category are amiodarone, quinidine, bretylium and sotalol. Because of the broad range of effects that antiarrhythmic agents may exert, safe and effective therapy requires a thorough familiarity with the pharmacologic profile of each drug administered and a careful evaluation of the presenting condition and the patient history. In some cases, a multiple drug regimen may be most appropriate. Various combinations such as class IA and IB agents, have been shown to slow conduction synergistically and increase refractoriness while keeping adverse effects to a minimum.

Effects of quinidine versus procainamide on the QT interval

Eighteen patients were given quinidine and procainamide separately to evaluate whether prolongation of the QT interval by type Ia antiarrhythmic agents is a drug-specific phenomenon. Doses were titrated to achieve standard trough therapeutic levels of quinidine (2 to 5 micrograms/ml) and procainamide (4 to 12 micrograms/ml). In 16 of the 18 patients, the increase in corrected QT interval (QTc) was greater with quinidine than with procainamide, averaging 78 +/- 10 ms (+/- standard error of the mean) with quinidine and 39 +/- 7 ms with procainamide (p less than 0.001). The greater degree of QTc prolongation with quinidine than with procainamide was not due to differences in sinus cycle length, QRS duration, serum potassium level or concomitant drug therapy. Differences in relative drug level did not appear to account for the greater effect of quinidine. Thus, at frequently used plasma levels, quinidine prolongs QTc to a greater degree than does procainamide. This effect does not appear to be due to the comparison of "nonequivalent" drug levels.

Pharmacology, electrophysiology, and pharmacokinetics of mexiletine

Mexiletine is a class I antiarrhythmic agent that is active after both oral and intravenous administration and similar in structure and activity to lidocaine. It decreases phase O maximal rate of depolarization (Vmax) by fast sodium channel blockade. The marked rate dependence of Vmax depression may explain mexiletine's lack of effect on normal conduction and its efficacy against ventricular tachyarrhythmias. Mexiletine significantly decreases the relative refractory period in His-Purkinje fibers without changing the sinus rate or atrioventricular and His-Purkinje conduction times. Action potential duration is usually shortened. Mexiletine may aggravate preexisting impairment of impulse generation and conduction. Uptake and distribution of mexiletine are rapid, systemic bioavailability is about 90%, and tissue distribution is extensive. Mexiletine is primarily metabolized in the liver; 10% to 15% is excreted unchanged in the urine. Elimination half-life is 9 to 11 hours after intravenous or oral administration. Microsomal enzyme induction shortens mexiletine's elimination half-life, whereas hepatic disease and acute myocardial infarction prolong it. Renal disease has little effect, although hemodialysis increases mexiletine clearance. Plasma concentrations from 0.75 to 2.0 mg/L are usually associated with a desirable therapeutic response.

Sustained release disopyramide compared to plain capsules after change-over from intravenous infusion

The plasma concentration profile of disopyramide was examined in 13 patients with arrhythmias following acute myocardial infarction. Intravenous loading doses of 1.5 mg/kg followed by 0.7 mg/kg and then infusion of 0.3 mg kg-1h-1 resulted in final concentrations between 2.4 and 4.9 mg l. Change-over to oral therapy with disopyramide sustained release (SR) tablets was smooth, and therapeutic plasma concentrations were maintained throughout. Comparison of the plasma concentrations in a subsequent cross-over study with disopyramide plain capsules 150 mg every 6 h and SR tablets 250 mg every 12 h, each being administered for 3 days to attain a steady state, showed that the bioavailability and the variation of the plasma concentration were similar with both regimens. In patients with body weight between 62 and 92 kg disopyramide SR tablets 250 mg every 12 h matched the preceding infusion rate of 0.3 mg kg-1h-1 resulting in plasma concentrations close to steady state already on the first day of oral therapy. The absorption of disopyramide SR tablets is only moderately delayed, and the preparation can be used twice daily in direct succession of intravenous infusion.

Some consequences of drug choice and dosage regimen for patients with impaired kidney function

The object of this article is to discuss difficulties in extrapolating the performances of a drug for which the kinetic parameters are derived in healthy volunteers, to patients with severely impaired kidney function. The theoretical background of some actual or probable background is given, and a possible solution for these problems is offered, that is, choosing another drug from the same drug group. In patients without kidney function, metabolism is the only pathway of elimination. When the elimination of the metabolite formed occurs by means of renal excretion only, this metabolite accumulates in patients with impaired or absent kidney function. When a metabolic pathway of the parent drug is part of a metabolic equilibrium, the metabolic return reaction results in an "apparent parent compound," with a half-life identical to that of the accumulated metabolite. In this way, the concentration of the "apparent" parent compound increases and the half-life of the sum of parent and "apparent" parent drug will change. Examples of this drug behavior are given for sulfamethoxazole, sulfametrole, sulfamethizole, procainamide, and N4-acetylprocainamide.

Cimetidine-procainamide pharmacokinetic interaction in man: evidence of competition for tubular secretion of basic drugs

The hypothesis that basic drugs can compete for active tubular secretion by the kidney was tested in six healthy volunteers by comparing the single dose pharmacokinetics of oral procainamide before and during a daily dose of cimetidine. The area under the procainamide plasma concentration-time curve was increased by cimetidine by an average of 35% from 27.0 +/- 0.3 micrograms/ml X h to 36.5 +/- 3.4 micrograms/ml X h. The elimination half-life increased from an harmonic mean of 2.92 to 3.68 h. The renal clearance of procainamide was reduced by cimetidine from 347 +/- 46 ml/min to 196 +/- 11 ml/min. All these results were statistically significant (p less than 0.016). The area under the plasma concentration-time curve for n-acetylprocainamide was increased by a mean of 25% by cimetidine due to a significant (p less than 0.016) reduction in renal clearance from 258 +/- 60 ml/min to 197 +/- 59 ml/min. The data suggests that cimetidine inhibits the tubular secretion of both procainamide and n-acetylprocainamide, and, if so, represents the first documented evidence for this type of drug interaction in man. The clinical implications from this study necessitate dosage adjustments of procainamide in patients being concomitantly treated with cimetidine. The interaction is pertinent not only for basic drugs that are cleared by the kidney, but also for metabolites of basic drugs and endogenous substances which require active transport into the lumen of the proximal tubule of the kidney for their elimination.

Plasma binding of disopyramide and mono-N-dealkyldisopyramide

1 Measuring total plasma levels of disopyramide (DP) and the main metabolite mono-N-dealkyldisopyramide (MND) in patients on maintenance therapy with DP has shown concentrations of MND comparable with those of DP, with wide intersubject variations. 2 A method which permits simultaneous measurement of unbound fraction of DP and MND has been developed. 3 In healthy subjects the unbound fraction of both DP and MND was concentration dependent, i.e. increased with higher concentrations of DP or MND. 4 The plasma protein binding of DP is altered by varying concentrations of MND. Clinically relevant concentrations of MND may increase the unbound fraction of DP approximately twofold. 5 The plasma protein binding of MND is also altered by varying concentrations of DP. Variation in the concentration of DP from the lower to the upper part of the therapeutic range may cause a 1.5-fold increase in the unbound fraction of MND. 6 In the assumed therapeutic range of 6-15 mumol DP/L, the interpatient variance of unbound DP concentration might be ten-fold or even higher. The present findings indicate the need for monitoring unbound drug concentrations in any attempt to establish plasma concentration/effect relationship.