The historical development, cellular electrophysiology and pharmacology of amiodarone

Enhancing Biopharmaceutical Attributes of Khellin by Amorphous Binary Solid Dispersions

Khellin, a furanochromone isolated from fruits and seeds of Ammi visnaga, is traditionally used in many eastern Mediterranean countries. The plant decoction and the crystalline substance khellin have many pharmacological activities. For instance, it acts as a bronchodilator and also relieves renal colic and urethral stones, etc. However, the low water solubility (~ 120 µg/mL) and low bioavailability limit its therapeutic application. Thus, the present research explores the development of its binary and ternary solid dispersion formulations to improve its solubility and dissolution behavior. A 24-well plate miniaturized protocol was established to identify the optimal hydrophilic polymer to prepare its solid dispersions. PEG-4000 was recognized as the favorable hydrophilic carrier in preparation of solid dispersion, SSB17. The formulation displayed ~ five-fold enhancement in the aqueous solubility of khellin. The binary solid dispersion SSB17 was manufactured at a gram scale and evaluated using ¹H-NMR, ¹³C-NMR, FT-IR, p-XRD, SEM, DSC, in vitro dissolution, and predicted pharmacokinetics. The quantitative dissolution data of SSB17 demonstrated ~ 2-3-fold improvement in AUC at physiological pH conditions. These conclusions highlight the basis for further preclinical studies on solid dispersions of khellin with improved biopharmaceutical properties.

Clinical effects of intravenous to oral amiodarone transition strategies in critically ill adult patients

WHAT IS KNOWN AND OBJECTIVE

There is limited guidance on how to transition critically ill patients from intravenous (IV) to oral (PO) amiodarone. The objective of this study was to assess the impact of IV and PO amiodarone overlap on short-term tachyarrhythmia recurrence and adverse hemodynamic outcomes in the intensive care unit.

METHODS

This is a retrospective, single-center analysis of critically ill adults who were treated with IV amiodarone for a supraventricular arrhythmia with rapid ventricular rate (RVR) and transitioned to PO amiodarone while inpatient. Patients were excluded if rate control was not achieved prior to the PO transition. Receipt of concomitant IV and PO therapy for ≤2 hours was considered no overlap (NOV) and >2 hours was considered overlap (OV). Tachyarrhythmia recurrence and adverse hemodynamic events were compared between groups.

RESULTS

A total of 90 patients (45 NOV, 45 OV) were included in the analysis. The median overlap duration was 0.1 (-1.3 to 1.2) hours in the NOV arm and 4 (2.6-6.1) hours in the OV arm. Recurrence of RVR occurred in 9 (20%) patients in each arm (P = 1.0). The median time from IV discontinuation to return of tachyarrhythmia was 10.5 hours. There were no significant differences in amiodarone dosing, electrolyte abnormalities, volume status or concomitant cardiac medications at the time of IV to PO transition. Hypotension occurred in 13% and 20% (P = 0.369) and bradycardia in 9% and 13% (P = 0.502) of patients in the NOV and OV arms, respectively.

WHAT IS NEW AND CONCLUSION

Providing IV and PO overlap of amiodarone for a median of 4 hours did not decrease the rate of early tachyarrhythmia recurrence. Future studies are warranted to evaluate the impact of alternative amiodarone dosing strategies on breakthrough tachyarrhythmia.

Amiodarone-Induced Third Degree Atrioventricular Block and Extreme QT Prolongation Generating Torsade Des Pointes in Paroxysmal Atrial Fibrillation

Amiodarone is still the most potent antiarrhythmic drug in the prevention of life threatening ventricular arrhythmias and demonstrates a very low incidence of torsade de pointes. An unusual case of an 81-year-old woman who developed serious abnormalities of the conduction system of the heart and torsade des pointes during intravenous infusion of amiodarone for the treatment of paroxysmal atrial fibrillation is described. To the best of our knowledge, this is the first case showing an association of intravenous amiodarone-induced third degree atrioventricular block and extreme QT interval prolongation generating torsade des pointes in a patient with paroxysmal atrial fibrillation who required an implantable cardioverter-defibrillator. Currently, amiodarone is still one of the few remaining treatment options for the medical therapeutic management of serious ventricular arrhythmias and to reduce the incidence of atrial fibrillation without increasing mortality or sudden cardiac death rates in heart failure patients like our elderly present patient. Nevertheless, we have to keep in mind that intravenous amiodarone may generate serious abnormalities of the conduction system of the heart and lethal ventricular arrhythmias in certain patients.

Cardiology: Post-Cardiothoracic Surgery Atrial Fibrillation: A Review of Preventive Strategies

Objective:

To review the available literature addressing preventive strategies of post-cardiothoracic surgery atrial fibrillation (post-CTS atrial fibrillation).

Data Sources:

Pertinent articles related to the etiology, risk factors, and preventive strategies were identified through a MEDLINE search (1966–March 2007) using the MeSH terms atrial fibrillation, cardiothoracic surgery, cardiac surgery, etiology, neurohormonal, sympathetic, volume, fluid, inflammation, risk factors, operative, pacing, β-adrenergic blockers, amiodarone, sotalol, calcium-channel blockers, magnesium, HMG-CoA reductase inhibitors, statins, fatty acids, PUFA, steroids, and nonsteroidal antiinflammatory drugs.

Study Selection and Data Extraction:

Articles evaluated were limited to human studies, published in the English language, with a Jadad score greater than 3. References of identified articles were reviewed for additional pertinent articles.

Data Synthesis:

Post-CTS atrial fibrillation most commonly occurs on the second or third postoperative day, with an incidence of 20–50%. Etiology theories include neurohormonal activation, volume overload, and inflammation. Studies examining nonpharmacologic therapies have shown that maintenance of the anterior epicardial fat pad is not a viable prophylactic strategy. Biatrial cardiac pacing, especially in combination with amiodarone, is a viable preventive option. Withdrawal of preoperative β-blockers places patients at higher risk for atrial fibrillation; these drugs should be continued postoperatively. Evidence exists supporting the use of amiodarone, sotalol, and magnesium in addition to β-blockers. Since most of these strategies work by attenuating neurohormonal activation, adverse events, including hypotension and bradycardia, are of concern. Adding agents with antiinflammatory properties, including hydroxymethylglutaryl coenzyme A reductase inhibitors or corticosteroids, may prove to be of benefit. Additional studies using novel therapies are needed in addition to established preventive strategies.

Conclusions:

Available evidence supports the continuation of preoperative β-blockers, as well as prophylactic amiodarone, sotalol, and magnesium. Other novel therapies, mostly targeting inflammation, are under investigation and may provide additional strategies.

Effects of early amiodarone administration during and immediately after cardiopulmonary resuscitation in a swine model

BACKGROUND

Aim of this experimental study was to compare haemodynamic effects and outcome with early administration of amiodarone and adrenaline vs. adrenaline alone in pigs with prolonged ventricular fibrillation (VF).

METHODS

After 8 min of untreated VF arrest, bolus doses were administered of adrenaline (0.02 mg/kg) and either amiodarone (5 mg/kg) or saline (n = 8 per group) after randomisation. Cardiopulmonary resuscitation (CPR) was commenced immediately after drug administration, and defibrillation was attempted 2 min later. CPR was resumed for another 2 min after each defibrillation attempt, and the same dose of adrenaline was given every 4th minute during CPR. Haemodynamic monitoring and mechanical ventilation continued for 6 h after return of spontaneous circulation (ROSC), and the pigs were euthanised at 48 h. Researchers were blinded for drug groups throughout the study.

RESULTS

There was no difference in rates of ROSC and 48-h survival with amiodarone vs. saline (5/8 vs. 7/8 and 0/8 vs. 3/8, respectively). Diastolic aortic pressure and coronary perfusion pressure were significantly lower with amiodarone during CPR and 1 min after ROSC (P < 0.05). The number of electric shocks required for terminating VF, time to ROSC and adrenaline dose were significantly higher with amiodarone (P < 0.01). The incidence of post-resuscitation tachyarrhythmias tended to be higher in the saline group (P = 0.081).

CONCLUSION

Early administration of amiodarone did not improve ROSC or 48-h survival rates, and was associated with worse haemodynamics in this swine model of cardiac arrest.

Amiodarone supplants lidocaine in ACLS and CPR protocols

Amiodarone is an antiarrhythmic medication used to treat and prevent certain types of serious, life-threatening ventricular arrhythmias. Amiodarone gained slow acceptance outside the specialized field of cardiac antiarrhythmic surgery because the side-effects are significant. Recent adoption of amiodarone in the ACLS (Advanced Cardiac Life Support) protocol has somewhat popularized this class of antiarrhythmics. Its use is slowly expanding in the acute medicine setting of anesthetics. This article summarizes the use of Amiodarone by anesthesiologists in the operating room and during cardiopulmonary resuscitation.

Effects of pink grapefruit juice on QT variability in patients with dilated or hypertensive cardiomyopathy and in healthy subjects

Recent evidence shows that pink grapefruit juice, which is a recommended dietary addition that contains high amounts of the antioxidant flavonoid naringenin, prolongs the corrected QT (QT(c)), a noninvasive electrophysiological marker of spatial myocardial repolarization, and does so by inhibiting the rapid component of the delayed rectifier K+ current (I(Kr)). Prompted by the observation that all class III antiarrhythmic drugs inhibit this current, thereby sometimes provoking torsades de pointes, we compared the effects of a liter of freshly squeezed pink grapefruit juice with those of 2 commonly used class III antiarrhythmics amiodarone and sotalol on the major noninvasive markers of temporal variability in myocardial repolarization used to stratify the risk of sudden death from malignant ventricular arrhythmias. In 32 subjects, 10 with postischemic dilated cardiomyopathy, 12 with hypertensive cardiomyopathy, and 10 healthy, we assessed QT(c) and QT variability index (QTVI) after administration of fresh pink grapefruit juice, placebo, amiodarone, or sotalol. After pink grapefruit juice and sotalol, all these indexes increased significantly from values observed after placebo (P<0.05) and from values after amiodarone (P<0.05). Conversely, after amiodarone, QT(c), but not QTVI, increased significantly from values after placebo (P<0.05). Presumably because of its high naringenin glycoside content, pink grapefruit juice prolongs cardiac repolarization and concurrently increases temporal cardiac repolarization dispersion. The potential proarrhythmic actions of pink grapefruit juice might be of concern in patients with major myocardial structural disorders.

Long-term amiodarone treatment causes cardioselective hypothyroid-like alteration in gene expression profile

The long-term cardiac effects of amiodarone resemble many aspects of hypothyroidism. The anti-arrhythmic potential of amiodarone may therefore be the result of a drug-induced, local hypothyroid-like condition. To investigate this controversial issue, we compared gene expression profiles in the hearts of rats treated with amiodarone with those of rats with hypothyroidism. Wistar male rats were assigned to 3 groups (n=6-8): Control, systemic hypothyroidism (hypothyroidism) and amiodarone treatment (amiodarone, 150 mg/kg/day, p.o., 4 weeks). Electrocardiogram (ECG) recordings, gene profiling by DNA microarray and Northern blotting were carried out. Amiodarone, like hypothyroidism, caused significant prolongation of RR and QT intervals in ECGs. Microarray analysis of 8435 genes in the left ventricular myocardium revealed a significant similarity in expression profiles between hypothyroidism and amiodarone (R=0.63, p<0.00001). The gene expression profiles of hypothyroidism and amiodarone showed closer correlation when top 100 up-regulated and 100 down-regulated genes in hypothyroidism (total 200 genes) were analyzed (R=0.78, p<0.00001). Northern blots of left ventricular myocardium showed a parallel decrease in mRNAs for myosin heavy chain (MHC)-alpha and a parallel increase for myosin heavy chain (MHC)-beta in hypothyroidism and amiodarone. In the liver and pituitary, in contrast, Northern blots showed quite different changes in the transcripts of the representative T3-responsive genes in the hypothyroidism and amiodarone. In conclusion, long-term treatment with amiodarone causes cardioselective hypothyroid-like alterations in gene expression profiles. The potent anti-arrhythmic activity of amiodarone may be attributable, in part at least, to this unique transcriptional remodeling.

Atrial fibrillation in the Wolff-Parkinson-White syndrome: ECG recognition and treatment in the ED

Estimated to occur in 0.1% to 0.3% of the population, Wolff-Parkinson-White syndrome (WPW) is a condition where atrial impulses bypass the atrioventricular node and activate the ventricular myocardium directly via an accessory pathway. Clinical clues to the diagnosis include a young patient with previous episodes of palpitations, rapid heart rate, or syncope. Although several different rhythm presentations are possible, atrial fibrillation is a not infrequent dysrhythmia seen in the WPW patient. Electrocardiographic features suggestive of WPW atrial fibrillation include irregularity of the rhythm; a very rapid ventricular response; presence of a delta wave; and a wide, bizarre QRS complex. Stable patients suspected of having this condition should not receive agents that predominantly block atrioventricular conduction, but they may be treated with procainamide or ibutilide. If instability is present, electrical cardioversion is required.

Short- and Long-Term Amiodarone Treatments Regulate Cav3.2 Low-Voltage-Activated T-type Ca2+ Channel through Distinct Mechanisms

Low-voltage-activated T-type Ca2+ channels have been recognized recently in the mechanisms underlying atrial arrhythmias. However, the pharmacological effects of amiodarone on the T-type Ca2+ channel remain unclear. We investigated short- and long-term effects of amiodarone on the T-type (Cav 3.2) Ca2+ channel. The Cav3.2 alpha1H subunit derived from human heart was stably transfected into cells [human embryonic kidney (HEK)-Cav3.2] cultured with or without 5 muM amiodarone. Patch-clamp recordings in the conventional whole-cell configuration were used to evaluate the actions of amiodarone on the T-type Ca2+ channel current (ICa.T). Amiodarone blockade of ICa.T occurred in a dose- and holding potential-dependent manner, shifting the activation and the steady-state inactivation curves in the hyperpolarization direction, when amiodarone was applied immediately to the bath solution. However, when the HEK-Cav3.2 cells were incubated with 5 microM amiodarone for 72 h, ICa.T density was significantly decreased by 31.7+/-2.3% for control,-93.1+/-4.3 pA/pF (n=8), versus amiodarone,-56.5+/-3.2 pA/pF (n=13), P<0.001. After the prolonged administration of amiodarone, the activation and the steady-state inactivation curves were shifted in the depolarization direction by -7.1 (n=41) and -5.5 mV (n=37), respectively, and current inactivation was significantly delayed [time constant (tau): control, 13.3+/-1.1 ms (n=6) versus amiodarone, 39.6+/-5.5 ms (n=6) at -30 mV, P<0.001)]. Nevertheless, short-term inhibitory effects of amiodarone on the modified T-type Cav3.2 Ca2+ channel created by long-term amiodarone treatment were functionally maintained. We conclude that amiodarone exerts its short- and long-term inhibitory actions on ICa.T via distinct blocking mechanisms.

Acute cardiodepressant effects induced by bolus intravenous administration of amiodarone in rabbits

Amiodarone is a potent anti-arrhythmic with a large pharmacological spectrum that shares the mechanisms of action of all classes of anti-arrhythmic drugs. Originally used in the treatment of supraventricular arrhythmias, it has also been used to treat ventricular tachyarrhythmias. The recent inclusion of amiodarone in the Advanced Cardiac Life Support protocols warrants the characterization of the hemodynamic profile resulting from the rapid venous administration of the drug. Thus, the main purpose of the present study was to investigate the acute hemodynamic profile resulting from the bolus i.v. injection of amiodarone, compared with bolus i.v. administration of lidocaine. We investigated the acute hemodynamic effects of amiodarone and lidocaine, in an experimental model of open-chest pentobarbital-anesthetized rabbits (n = 24). Amiodarone (5 mg/kg) induced immediate reductions in mean arterial pressure (MAP) of 32 +/- 5% (P < 0.001), accompanied by reductions in cardiac contractility and relaxation, as assessed by left ventricular (LV) +dP/dt(max) and -dP/dt(max) (40 +/- 4 and 36 +/- 4% respectively) (P < 0.001), heart rate (HR) 10 +/- 1% (P < 0.05), cardiac output (CO) 24 +/- 5% (P < 0.001) and systemic vascular resistance (SVR) 19 +/- 3.5% (P < 0.05). Lidocaine (3 mg/kg) induced reductions in: MAP of 18 +/- 7% (P < 0.001), LV +dP/dt(max) and -dP/dt(max) (40 +/- 5 and 22 +/- 7% respectively) (P < 0.001), HR 7 +/- 1% (P < 0.01) and CO of 23 +/- 6% (P < 0.001). SVR increased by 9 +/- 1.5% (P > 0.05). It is concluded that rapid i.v. administration of both amiodarone and lidocaine induces significant cardiovascular depression mainly characterized by immediate reductions in cardiac contractility.

Amiodarone Use in Patients with Documented Allergy to Iodine-Containing Compounds

The popularity of amiodarone has grown due to its effectiveness in converting arrhythmia and its formulation availability. Formulations of the drug also contain iodine; the iodine content is 75 mg in a 200-mg tablet of amiodarone and 18.7 mg/ml in the intravenous solution. Approximately 10% of the iodine content of oral amiodarone is released into the circulatory system and may increase the risks of hypersensitivity reactions in iodine-sensitive patients. Documented allergies to contrast media or shellfish should not imply that a patient is allergic to iodine. Reactions to contrast media are likely due to the high osmolar or ionic content of the dye. The primary allergen in shellfish that stimulates allergic reactions is tropomyosin. Although amiodarone can cause thyroid disorders due to the high iodine load delivered to the body with each dose, no known association exists between amiodarone and reactions to contrast media or shellfish. Three patients whose medical charts listed an allergy to iodine were administered amiodarone for chemical cardioversion of arrhythmia to normal sinus rhythm. No anaphylactic or anaphylactoid reactions were observed in any of the patients during oral or intravenous amiodarone administration. In patients with true iodine hypersensitivity, however, the potential for such reactions exists.

Appropriate dosing of antiarrhythmic drugs in Japan requires therapeutic drug monitoring*

OBJECTIVE

In general, drugs are used in accordance with an approved dosage regimen in expectation of an appropriate balance between efficacy and toxicity. However, dose control of drugs with a narrow therapeutic range and marked intersubject variability in pharmacokinetics should be established through individualization of dosing based on therapeutic drug monitoring (TDM). The purpose of this study was to examine differences between the approved dosage regimen and the doses of antiarrhythmic drugs and digoxin used in clinical practice and to examine the influence of TDM on dosing.

METHODS

Prescription research of antiarrhythmic drugs was performed at five national hospitals in Japan. Prescriptions for antiarrhythmic drugs (cibenzoline, disopyramide, pirmenol, mexiletine, aprindine, flecainide, pilsicainide, amiodarone and digoxin) were counted for the study period. The mean dose and dose distribution of the drugs were determined in each hospital. Comparisons were made of mean dose obtained in the study with the dosage approved by the authority. In addition, the percentage of patients that received TDM was determined.

RESULTS

A difference was seen between the approved dosage and the actual dose. For all drugs except flecainide, the mean dose was smaller than the approved dosage. For all drugs except digoxin, remarkable variations were seen in the dose distribution among the hospitals. Digoxin showed a similar dose distribution among the five hospitals. Overall, the percentage of patients that received TDM was low except for Hospital A. However, TDM of digoxin was relatively common at four of the hospitals.

CONCLUSIONS

It is concluded that, with the exception of digoxin, the appropriate dosing regimen for antiarrhythmic drugs is not yet established. The establishment of appropriate dosing regimens for antiarrhythmic drugs requires the more widespread adoption of TDM.

Time course of fibrillation and defibrillation thresholds after an intravenous bolus of amiodarone--an experimental study

Experimental studies have described an increase in ventricular fibrillation threshold (VFT) by intravenous amiodarone. The aim of this study was to examine the early time course of changes in VFT and defibrillation thresholds (DFT) after an intravenous bolus of amiodarone in an experimental pig model of transient myocardial ischemia.

METHODS AND RESULTS

VFT and relative effective ventricular refractory period (ERP) were measured in 15 anaesthetized open-chest pigs after 3 min of regional coronary ischaemia before (time 0) and 2, 15, 30, 60, and 90 min after the intravenous injection of normal saline (group A, n = 5) or amiodarone, 5 mg/kg over 15 s (group B, n = 10). DFT was measured by increasing the strength of DC shocks until defibrillation was accomplished. Amiodarone caused an increase in VFT, starting at 2 min after the infusion (11.4 +/- 8.4 mA versus 9.2 +/- 4.6 mA, P = 0.03), became significant at 15 min (13.7 +/- 6.5 mA, P = 0.009), continued to rise at 30 min (34.2 +/- 28.7 mA, P = 0.03) and reached a plateau at 60 min (50.3 +/- 37.8 mA, P = 0.008). An increase was also observed in the ERP (204 +/- 25 ms at 2 min versus 197 +/- 26 ms at baseline, P = 0.074, 211 +/- 38 ms at 15 min, P = 0.084, 212 +/- 40 ms at 30 min, P = 0.037, 220 +/- 34 ms at 60 min, P = 0.002, and 227 +/- 32 ms at 90 min, P = 0.008). No change was observed in DFT after amiodarone administration. No significant change in VFT, ERP, or DFT occurred in the control group.

CONCLUSION

In this porcine model, the intravenous administration of amiodarone increased VFT and ERP over 60 min after the injection, without effect on DFT.

Predictors of new malignant ventricular arrhythmias after coronary surgery

OBJECTIVES

We sought to investigate the relationship between perioperative factors and the occurrence of ventricular tachycardia (VT) and ventricular fibrillation (VF), as well as the impact of VT/VF on early and late mortality.

BACKGROUND

Both VT and VF are rare but serious complications after coronary artery bypass graft surgery (CABG), and their etiology and implications remain uncertain.

METHODS

Data on 4,411 consecutive patients undergoing CABG (1,154 [25.8%] had off-pump surgery) between April 1996 and September 2001 were extracted from a prospective database and analyzed. Odds ratios (ORs) describing associations between possible risk factors and VT/VF were estimated separately. Factors observed to be significantly associated with VT/VF were further investigated using multivariate logistic regression.

RESULTS

Sixty-nine patients suffered VT/VF (1.6%). There were 61 (1.4%) in-hospital/30-day deaths, 15 among patients who had postoperative VT/VF (21.7%). Patient factors independently associated with an increase in the odds of VT/VF included age <65 years, female gender, body mass index <25 kg/m(2), unstable angina, moderate or poor ejection fraction, and the need for inotropes and an intra-aortic balloon pump (OR 1.72 to 4.47, p < 0.05). After adjustment, off-pump surgery was associated with a substantial but nonsignificant protective effect against VT/VF (OR 0.53, 95% confidence interval [CI] 0.25 to 1.13; p = 0.10). Actuarial survival at two years was 98.2% among patients who had VT/VF and who survived to discharge/30 days, compared with 97.0% for the control group (adjusted hazard ratio 0.96 (95% CI 0.40 to 2.31, p = 0.92).

CONCLUSIONS

The incidence of VT/VF is low in patients undergoing coronary surgery but is associated with high in-hospital mortality. The late survival of the discharged VT/VF patients compares favorably with that of controls.

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.

Acute electrophysiologic effects of intravenous amiodarone are independent of a sympatholytic action in humans

Previous experiments in animals demonstrated a novel sympatholytic action of acute intravascular amiodarone (AM). It is not known if this action also occurs in humans. Twelve male volunteers performed handgrip for 10 min before and after 300 mg intravenous (IV) AM over 60 min. The effect of handgrip was determined from changes in blood pressure (BP), heart rate (HR), and cardiac noradrenaline (NA) spillover. Changes in cardiac spillover of dihydroxyphenylglycol (DHPG), the metabolite of NA, were measured during AM infusion. The electrophysiological effects of AM were determined from changes to the A-H intervals during right atrial stimulation (100 beats/min). Handgrip increased HR (63 +/- 2 to 84 +/- 5 beats/min and 65 +/- 3 to 84 +/- 4 beats/min), systolic BP (141 +/- 4 to 179 +/- 6 mm Hg and 140 +/- 4 to 179 +/- 7 mm Hg), and cardiac NA spillover (11.9 +/- 4 to 44.3 +/- 13 ng/min and 17.3 +/- 4 to 55.5 +/- 11 ng/min) before and after AM, respectively (P < 0.02 in all groups). There was good correlation between increases in cardiac NA spillover and HR (r2 = 0.86) and systolic BP (r2 = 0.87). AM increased the A-H interval (95.5 +/- 18 to 107.8 +/- 20 ms, P < 0.02). There was no difference in hemodynamic or NA response to handgrip before or after the AM infusion. There was also no change in DHPG cardiac spillover during AM infusion. Acute IV AM did not exert a sympatholytic action in humans, with no attenuation in hemodynamic or NA response to handgrip or increase in DHPG production, despite producing an electrophysiologic response.

Intravenous Amiodarone for the Treatment of Atrial Fibrillation in the Nonsurgical Patient

Purpose: To review the literature to define the efficacy of intravenous (IV) amiodarone in the treatment of atrial fibrillation in the nonsurgical patient. Method: A MEDLINE search was conducted using the key words “intravenous amiodarone” and “atrial fibrillation.” All trials evaluating the use of intravenous amiodarone in the surgical setting were excluded. Results: Twenty articles were identified, which were divided into acute and chronic atrial fibrillation. Within the acute setting, IV amiodarone was used alone, compared to a placebo-control, or compared to active drug regimens. In the trials without a control group, it was difficult to determine how much of the effect was due to spontaneous conversion. When compared to placebo, IV amiodarone offered a 61% to 92% conversion at 24 hours. Compared to active drug therapy, there was a trend to increased efficacy at 24 hours. However, amiodarone was no more effective for the conversion of atrial fibrillation than alternative therapies. In the case of chronic atrial fibrillation, intravenous amiodarone had no benefit. The incidence of thrombophlebitis, bradycardia, and hypotension was quite high, reported to be around 15% to 30% in many of the trials. Conclusion: The use of intravenous amiodarone should not be recommended as the first line agent for the conversion of atrial fibrillation.

A comparison of two individual amiodarone regimens to placebo in open heart surgery patients

BACKGROUND

This study compares the ability of two oral amiodarone regimens to reduce the risk of atrial fibrillation (AF) as compared with the placebo among elderly open heart surgery (OHS) patients receiving beta blockade.

METHODS

This is a randomized, double-blinded, placebo-controlled trial of 220 patients undergoing OHS. Patients (average age, 73 years) received 7 g of oral amiodarone more than 10 days starting 5 days before OHS (slow load; n = 56), a 6 g oral amiodarone regimen more than 6 days starting 1 day before OHS (fast load; n = 64), or matching placebo in one of the two previously mentioned regimens (n = 100).

RESULTS

Patients receiving the slow load amiodarone regimen had a significant reduction in the risk of AF (48.4%; p = 0.013), AF lasting more than 24 hours (76.5%; p = 0.003), symptomatic AF (90.0%; p = 0.002), and recurrent AF (64.5%; p = 0.025) as compared with the placebo. Patients receiving the fast load amiodarone regimen had significant reductions in the risk of AF lasting more than 24 hours (52.6%; p = 0.038) and symptomatic AF (65.0%; p = 0.024), but the incidence of any AF or any recurrence of AF only showed a trend toward significance (34.0% and 45.5%; p = 0.054 and 0.09, respectively).

CONCLUSIONS

Oral amiodarone in a slow loading regimen provides significant suppression of all AF factors and can be used when a patient has started it at least 5 days before OHS. If a patient has less than 5 days before OHS, the fast loading regimen is an efficacious alternative as it provides significant benefits in preventing AF from lasting more than 24 hours and for preventing symptomatic AF. Both regimens were well tolerated and safe in elderly patients receiving beta blockade according to the hospital's standard protocol.

Increased cardiac alpha-1-adrenoceptor density in rats following treatment with amiodarone

This study was undertaken to investigate the interaction between amiodarone and alpha-1-adrenoceptors in rat cardiac cells. The level (Bmax) and affinity (Kd) of alpha-1-adrenoceptors in heart cells were determined by [3H]prazosin radioligand binding following amiodarone treatment. In cultured intact cardiocytes treated for 48 h with 10 microM amiodarone, [3H]prazosin binding increased by 31% compared with the control cells (p<0.05). The increase was both dose and time dependent and was found to be specific because no significant change occurred in creatine kinase activity. Additionally, under the same conditions, an increase in [3H]prazosin binding to cultured cardiocyte cell membranes was also obtained. Oral gavage of amiodarone to rats for 8 d resulted in a 25% increase in [3H]prazosin binding to isolated ventricle membranes compared with control rats (p<0.05). We conclude that amiodarone treatment can increase the response to alpha-1-adrenoceptors agonist in the heart due to an increase in the density of alpha-1-adrenoceptors.

A review of class III antiarrhythmic agents for atrial fibrillation: maintenance of normal sinus rhythm

A noteworthy shift from class I to class III antiarrhythmic agents for suppression of atrial fibrillation has occurred. Sotalol, amiodarone, and dofetilide have been evaluated for their ability to maintain sinus rhythm in patients with chronic atrial fibrillation. All of these agents are moderately effective; however, amiodarone appears to be most efficacious. Aside from their common class III actions, these agents have profoundly different pharmacologic, pharmacokinetic, safety, and drug interaction profiles that help guide drug selection. Amiodarone and dofetilide are safe in patients who have had a myocardial infarction and those with heart failure. The safety of commercially available d,l-sotalol in these patients is poorly understood. Torsades de pointes is the most serious adverse effect of sotalol and dofetilide, and risk increases with renal dysfunction. Amiodarone has minimal proarrhythmic risk but has numerous noncardiac toxicities that require frequent monitoring. Overall, an ideal antiarrhythmic agent does not exist, and drug selection should be highly individualized.

Chronic amiodarone evokes no torsade de pointes arrhythmias despite QT lengthening in an animal model of acquired long-QT syndrome

BACKGROUND

Amiodarone is an effective antiarrhythmic drug rarely associated with torsade de pointes arrhythmias (TdP). The noniodinated compound dronedarone could resemble amiodarone and be devoid of the adverse effects. In the dog with chronic complete atrioventricular (AV) block (CAVB) and acquired long-QT syndrome, the electrophysiological and proarrhythmic properties of the drugs were compared after 4 weeks of oral treatment.

METHODS AND RESULTS

Amiodarone (n=7, 40 mg. kg(-1). d(-1)) and dronedarone (n=8, 20 mg/kg BID) were started at 6 weeks of CAVB (baseline). Six dogs served as controls. Surface ECGs and endocardially placed monophasic action potential catheters in the left (LV) and right (RV) ventricles were recorded to assess QTc time, action potential duration (APD), interventricular dispersion (DeltaAPD=LV APD minus RV APD), early afterdepolarizations (EADs), ectopic beats, and TdP. Both amiodarone (+21%) and dronedarone (+31%) increased QTc time. Amiodarone showed no increase in DeltaAPD in 4 of 7 dogs, whereas dronedarone augmented DeltaAPD in 7 of 8 animals. After dronedarone, TdP occurred in 4 of 8 dogs with the highest DeltaAPD (105+/-20 ms). TdP was never seen with amiodarone, not even in the dogs that had DeltaAPD values comparable to those with dronedarone. Furthermore, a difference existed in EADs and ectopic activity incidence (dronedarone 3 of 8; amiodarone 0 of 7), which was also seen during an epinephrine challenge.

CONCLUSIONS

In the CAVB dog model, both amiodarone and dronedarone prolong QT time (class III effect). The absence of TdP with amiodarone seems to be related to homogeneous APD lengthening in the majority of dogs and the lack of EADs and/or ventricular ectopic beats in all.

Oral amiodarone for prevention of atrial fibrillation after open heart surgery, the Atrial Fibrillation Suppression Trial (AFIST): a randomised placebo-controlled trial

BACKGROUND

Beta-blockers and amiodarone reduce the frequency of atrial fibrillation after open-heart surgery but the effectiveness of oral amiodarone in older patients already receiving beta-blockers is unknown. We have assessed the efficacy of oral amiodarone in preventing atrial fibrillation in patients aged 60 years or older undergoing open-heart surgery.

METHODS

We did a randomised, double-blind placebo-controlled trial in which patients undergoing open-heart surgery (n=220, average age 73 years) received amiodarone (n=120) or placebo (n=100). Patients enrolled less than 5 days before surgery received 6 g of amiodarone or placebo over 6 days beginning on preoperative day 1. Patients enrolled at least 5 days before surgery received 7 g over 10 days beginning on preoperative day 5.

FINDINGS

Patients on amiodarone had a lower frequency of any atrial fibrillation (22.5% vs 38.0%; p=0.01; absolute difference 15.5% [95% CI 3.4-27.6%]), and there were significant differences in favour of the active drug for symptomatic atrial fibrillation (4.2% vs 18.0%, p=0.001), cerebrovascular accident (1.7% vs 7.0%, p=0.04), and postoperative ventricular tachycardia (1.7% vs 7.0%, p=0.04). Beta-blocker use (87.5% amiodarone vs 91.0% placebo), nausea (26.7% vs 16.0%), 30-day mortality (3.3% vs 4.0%), symptomatic bradycardia (7.5% vs 7.0%), and hypotension (14.2% vs 10.0%) were similar.

INTERPRETATION

Oral amiodarone prophylaxis in combination with beta-blockers prevents atrial fibrillation and symptomatic fibrillation and reduces the risk of cerebrovascular accidents and ventricular tachycardia.

Short- and long-term effects of amiodarone on the two components of cardiac delayed rectifier K(+) current

BACKGROUND

Amiodarone is the most promising drug for the treatment of life-threatening tachyarrhythmias in patients with structural heart disease. The pharmacological effects of amiodarone on cardiac ion channels are complex and may differ for short-term and long-term administration.

METHODS AND RESULTS

The delayed rectifier K(+) current (I(K)) of ventricular myocytes isolated from rabbit hearts was recorded with the whole-cell voltage-clamp technique. I(K) was separated into 2 components by use of specific blockers for either I(Ks) (chromanol 293B, 30 micromol/L) or I(Kr) (E-4031, 10 micromol/L). Short-term application of amiodarone caused a concentration-dependent decrease in I(Kr) with an IC(50) of 2.8 micromol/L (n=8) but only a minimal reduction in I(Ks). The short-term effects of amiodarone were also determined in Xenopus oocytes expressing the cloned human channels that conduct I(Kr) and I(Ks) (HERG and KvLQT1/minK). HERG current in oocytes was reduced by amiodarone (IC(50)=38 micromol/L), whereas KvLQT1/minK current was unaffected by 300 micromol/L amiodarone. To study the effects of long-term drug administration, rabbits were treated for 4 weeks with oral amiodarone (100 mg. kg(-1). d(-1)) before cell isolation. Long-term administration of amiodarone decreased I(K) to 55% (n=10) in control rabbits and altered the relative density of I(Kr) and I(Ks). The majority (92%) of current was I(Kr). mRNA levels of rabbit ERG,KVLQT1, and minK in left ventricular myocardium did not differ between control and long-term amiodarone.

CONCLUSIONS

Amiodarone has differential effects on the 2 components of I(K), depending on the application period; short-term treatment inhibits primarily I(Kr), whereas long-term treatment reduces I(Ks).

E 047/1: a new class III antiarrhythmic agent

The efficacy, pharmacokinetics, safety, and tolerability of E 047/1, an amiodarone derivative, were evaluated in patients with acute supraventricular or ventricular arrhythmia. In an open, nonrandomized prospective multicenter trial, 20 patients were treated with three different i.v. dosage regimens of E 047/1. Arrhythmia termination indicated efficacy. Pharmacokinetics were determined by measurements of drug plasma levels. Safety was judged by changes of blood pressure, heart rate, ECG parameters, and appearance of adverse events. For local tolerability, effects at the site of infusion were assessed. In patients with atrial fibrillation and/or atrial flutter, drug plasma levels and prolongation of QT interval were correlated with efficacy. In 10 (50%) patients, therapeutic intervention with E 047/1 was successful. Drug plasma levels rapidly decreased within 1 h after administration. Blood pressure values and ECG parameters stayed constant during the observation period. Proarrhythmic effects were not observed. As adverse events, vertigo, vomiting, and nausea in three (15%) and hypotension in one (5%) patient, respectively, occurred in the high-dose bolus regimen only. At the site of infusion, no adverse effects were found. No dependency between drug plasma levels and arrhythmia termination was found. E 047/1 has proven to be efficient and safe in the treatment of arrhythmia. E 047/1 is characterized by rapid plasma elimination, absence of proarrhythmic or cardiodepressive effects, mild adverse events, and excellent local tolerability. For further investigation, we recommend a combined bolus- and weight-adapted infusion regimen.

Electrophysiological effects of dronedarone (SR33589), a noniodinated benzofuran derivative, in the rabbit heart : comparison with amiodarone

BACKGROUND

To overcome the side effects of amiodarone (AM), its noniodinated analogue, dronedarone (SR), was synthesized. In this study, its electrophysiological effects were compared with those of AM in rabbit hearts.

METHODS AND RESULTS

Five animal groups (n=7 each) for 3 weeks received daily oral treatment of 1 of these regimens: (1) control, vehicle only; (2) AM 50 mg/kg (AM50); (3) AM 100 mg/kg (AM100); (4) SR 50 mg/kg (SR50); and (5) SR 100 mg/kg (SR100). ECGs were recorded before drug and at 3 weeks of drug before euthanasia. Action potentials were recorded from isolated papillary muscle and sinoatrial node by microelectrode techniques. The short-term effects were studied in controls (n=5) at various concentrations of SR (0 to 10 micromol/L) in tissue bath. Action potential duration at 50% (APD(50)) and 90% (APD(90)) repolarization and upstroke dV/dt (V(max)) at various cycle lengths were compared by ANOVA with repeated measures. Compared with control, AM and SR increased RR, QT, and QTc intervals (P<0.0001 for all). Ventricular APD(50) and APD(90) were lengthened by 20% to 49% as a function of dose (P<0.005 to <0.0001) and cycle length (P<0.001). SR100 effects were greater than those of AM100 (P<0.002). V(max) was decreased by both AM100 (P<0.0001) and SR100 (P<0.01). Sinoatrial node automaticity was slowed in treated groups compared with that of the control group (P<0.0001 for all).

CONCLUSIONS

The electrophysiological effects of dronedarone are similar to those of AM but more potent, despite deletion of iodine from its molecular structure, a finding of importance for the development of future class III antiarrhythmic compounds.

Amiodarone: ionic and cellular mechanisms of action of the most promising class III agent

Amiodarone is the most promising drug in the treatment of life-threatening ventricular tachyarrhythmias in patients with significant structural heart disease. The pharmacologic profile of amiodarone is complex and much remains to be clarified about its short- and long-term actions on multiple molecular targets. This article reviews electrophysiologic effects of amiodarone based on previous reports and our own experiments in single cells and multicellular tissue preparations of mammalian hearts. As acute effects, amiodarone inhibits both inward and outward currents. The inhibition of inward sodium and calcium currents (I(Na), I(Ca)) is enhanced in a use- and voltage-dependent manner, resulting in suppression of excitability and conductivity of cardiac tissues especially when stimulated at higher frequencies and in those with less-negative membrane potential. Both voltage- and ligand-gated potassium channel currents (I(K), I(K,Na), I(K,ACh)) are also inhibited at therapeutic levels of drug concentrations. Acutely-administered amiodarone has no consistent effect on the action potential duration (APD). The major and consistent long-term effect of the drug is a moderate APD prolongation with minimal frequency dependence. This prolongation is most likely due to a decrease in the current density of I(K) and I(to). Chronic amiodarone was shown to cause a down-regulation of Kv1.5 messenger ribonucleic acid (mRNA) in rat hearts, suggesting a drug-induced modulation of potassium-channel gene expression. Tissue accumulation of amiodarone and its active metabolite (desethylamiodarone) may modulate the chronic effects, causing variable suppression of excitability and conductivity of the heart through the direct effects of the compounds retained at the sites of action. Amiodarone and desethylamiodarone could antagonize triiodothyronine (T3) action on the heart at cellular or subcellular levels, leading to phenotypic resemblance of long-term amiodarone treatment and hypothyroidism.

Impact of concurrent amiodarone treatment on the tolerability and efficacy of carvedilol in patients with chronic heart failure

OBJECTIVE

To assess the safety and efficacy of carvedilol when administered to heart failure patients already receiving amiodarone.

DESIGN

Retrospective analysis of the clinical outcome of 230 patients treated with carvedilol for chronic heart failure, stratified according to whether they were already receiving amiodarone (amiodarone group, 80 patients) or not (non-amiodarone group, 130 patients) at baseline.

SETTING

Heart failure clinic at a university affiliated public teaching hospital.

MAIN OUTCOME MEASURES

Incidence of adverse events; changes in functional status and echocardiographic dimensions at three months.

RESULTS

Adverse reactions to carvedilol occurred in 33 (41%) of the amiodarone group and 43 (29%) of the non-amiodarone group (p = 0.049). Carvedilol was discontinued in 21 (26%) of the amiodarone group and 37 (25%) of the non-amiodarone group (NS). The clinical outcome at three months did not differ significantly between the two groups; 31 (39%) of the amiodarone group improved their New York Heart Association status, 28 (35%) were unchanged, and 21 (26%) deteriorated compared with 67 (45%), 51 (34%), and 32 (21%), respectively, for the non-amiodarone group (NS). Both groups had highly significant decreases in heart rate and left ventricular end systolic dimension, and a significant increase in left ventricular ejection fraction after three months of carvedilol treatment, with no significant differences between the groups.

CONCLUSIONS

The beneficial effects of carvedilol on left ventricular remodelling, systolic function, and symptomatic status are not affected by concurrent treatment with amiodarone. Adverse reactions necessitating cessation of carvedilol are no more frequent in patients receiving amiodarone.

Amiodarone for resuscitation after out-of-hospital cardiac arrest due to ventricular fibrillation

BACKGROUND

Whether antiarrhythmic drugs improve the rate of successful resuscitation after out-of-hospital cardiac arrest has not been determined in randomized clinical trials.

METHODS

We conducted a randomized, double-blind, placebo-controlled study of intravenous amiodarone in patients with out-of-hospital cardiac arrest. Patients who had cardiac arrest with ventricular fibrillation (or pulseless ventricular tachycardia) and who had not been resuscitated after receiving three or more precordial shocks were randomly assigned to receive 300 mg of intravenous amiodarone (246 patients) or placebo (258 patients).

RESULTS

The treatment groups had similar clinical profiles. There was no significant difference between the amiodarone and placebo groups in the duration of the resuscitation attempt (42+/-16.4 and 43+/-16.3 minutes, respectively), the number of shocks delivered (4+/-3 and 6+/-5), or the proportion of patients who required additional antiarrhythmic drugs after the administration of the study drug (66 percent and 73 percent). More patients in the amiodarone group than in the placebo group had hypotension (59 percent vs. 48 percent, P=0.04) or bradycardia (41 percent vs. 25 percent, P=0.004) after receiving the study drug. Recipients of amiodarone were more likely to survive to be admitted to the hospital (44 percent, vs. 34 percent of the placebo group; P=0.03). The benefit of amiodarone was consistent among all subgroups and at all times of drug administration. The adjusted odds ratio for survival to admission to the hospital in the amiodarone group as compared with the placebo group was 1.6 (95 percent confidence interval, 1.1 to 2.4; P=0.02). The trial did not have sufficient statistical power to detect differences in survival to hospital discharge, which differed only slightly between the two groups.

CONCLUSIONS

In patients with out-of-hospital cardiac arrest due to refractory ventricular arrhythmias, treatment with amiodarone resulted in a higher rate of survival to hospital admission. Whether this benefit extends to survival to discharge from the hospital merits further investigation.

An assessment of the safety of short-term amiodarone therapy in cardiac surgical patients with fentanyl-isoflurane anesthesia

In previously published case reports and a retrospective study, investigators have noted that amiodarone may cause substantial hemodynamic instability when combined with fentanyl-containing anesthesia regimens. We performed the present study to evaluate the safety of short-term amiodarone therapy when combined with a fentanyl-containing anesthesia regimen in a randomized, double-blinded, placebo-controlled format. After institutional approval and written informed consent, patients scheduled to undergo coronary artery bypass grafting or valvular surgery were randomly allocated to receive amiodarone (3.4 g over 5 days or 2.2 g over 24 hours) or placebo before surgery. Four indicators for hemodynamic instability were assessed: 1) a net increase in fluid balance during surgery of >2 L; 2) use of dopamine at a rate >10 microg x kg(-1) x min(-1); 3) use of other vasopressive catecholamines; and 4) use of a phosphodiesterase inhibitor or intraaortic balloon pump. Systolic, diastolic, and central venous pressures were measured before fentanyl administration, before cardiopulmonary bypass (CPB), and after separation from CPB. Overall, 84 patients (45 patients in the amiodarone group, 39 in the placebo group) were enrolled and completed the study. There were no significant differences between the two groups in any indicator for hemodynamic instability or the indicators of instability combined. After CPB, there was a significantly lower systolic blood pressure in the amiodarone group compared with the placebo group (112 +/- 12 vs 117 +/- 14 mm Hg; P = 0.049). However, there was a trend toward smaller IV fluid requirements during surgery in the amiodarone group compared with the placebo group (438 +/- 867 vs 907 +/- 1640 mL; P = 0.09). We found no increased risk of hemodynamic compromise after short-term amiodarone therapy among patients receiving a fentanyl-containing anesthesia regimen during open heart surgery.

IMPLICATIONS

In previous retrospective studies and case reports, investigators have identified a possible risk of hemodynamic compromise when patients receiving chronic amiodarone therapy are given anesthesia regimens containing fentanyl. We performed a prospective, randomized, double-blinded study to evaluate the hemodynamic effects of short-term amiodarone therapy during fentanyl-isoflurane anesthesia for open heart surgery. No adverse hemodynamic effects of amiodarone were identified.

Beta-blocker use and survival in patients with ventricular fibrillation or symptomatic ventricular tachycardia: the Antiarrhythmics Versus Implantable Defibrillators (AVID) trial

OBJECTIVES

To evaluate whether use of beta-adrenergic blocking agents, alone or in combination with specific antiarrhythmic therapy, is associated with improved survival in persons with ventricular fibrillation (VF) or symptomatic ventricular tachycardia (VT).

BACKGROUND

The ability of beta-blockers to alter the mortality of patients with VF or VT receiving contemporary medical management is not well defined.

METHODS

Survival of 1,016 randomized and 2,101 eligible, nonrandomized patients with VF or symptomatic VT followed in the Antiarrhythmics Versus Implantable Defibrillators (AVID) trial through December 31, 1996 was assessed using Cox proportional hazards analysis.

RESULTS

The 817 (28%) patients discharged from hospital receiving beta-blockers had less ventricular dysfunction, fewer symptoms of heart failure and a different pattern of medication use compared with patients not receiving beta-blockers. Before adjustment for important prognostic variables, beta-blockade was not significantly associated with survival in randomized or in eligible, nonrandomized patients treated with specific antiarrhythmic therapy. After adjustment, beta-blockade remained unrelated to survival in randomized or in eligible, nonrandomized patients treated with amiodarone alone (n = 1142; adjusted relative risk [RR] = 0.96; 95% confidence interval [CI] 0.64-1.45; p = 0.85) or a defibrillator alone (n = 1347; adjusted RR = 0.88; 95% CI 0.55 to 1.40; p = 0.58). In contrast, beta-blockade was independently associated with improved survival in eligible, nonrandomized patients who were not treated with specific antiarrhythmic therapy (n = 412; adjusted RR = 0.47; 95% CI 0.25 to 0.88; p = 0.018).

CONCLUSIONS

Beta-blocker use was independently associated with improved survival in patients with VF or symptomatic VT who were not treated with specific antiarrhythmic therapy, but a protective effect was not prominent in patients already receiving amiodarone or a defibrillator.

Thyroid hormone alpha1 and beta1 receptor mRNA are downregulated by amiodarone in mouse myocardium

Amiodarone, a powerful antiarrhythmic drug, may exert its effect by antagonism of the thyroid hormone, probably at the receptor level. The aim of this study was to investigate whether amiodarone affects the levels of thyroid hormone receptor (TR) messenger RNA (mRNA) subtypes in mouse hearts. Mice were treated with 10, 25, and 50 mg/kg body weight (BW) amiodarone or vehicle (propyleneglycol) intraperitoneally, daily for 14 days. The heart rate dose-dependently decreased in the 25 mg/kg BW (p < 0.05) and 50 mg/kg BW (p < 0.005) amiodarone-treated mice compared with control. Serum T3 levels were significantly decreased by 25% (4.2 +/- 0.7 pM) in the 50 mg/kg BW amiodarone group in comparison to control (5.6 +/- 1.4 pM; p < 0.05). The serum T4 levels were 1.3 times higher in 50 mg/kg BW amiodarone-treated mice (13.2 +/-1.6 pM) compared with the control (10.3 +/- 1.3 pM; p < 0.005). Determination of TRalpha1, alpha2, beta1, and beta2 mRNA in the heart were performed by reverse transcriptase-polymerase chain reaction (RT-PCR)/enzyme-linked immunosorbent assay (ELISA). Both in treated and untreated mice, TRalpha2 mRNA had the highest density in mouse heart, whereas TRbeta2 mRNA had the lowest density. Amiodarone dose-dependently downregulated the levels of TRalpha1 and beta1 mRNA in comparison to the control. There were, however, no differences in the TRalpha2 and TRbeta2 mRNA levels in the mice heart treated with different doses of amiodarone in comparison with the control group. In conclusion, this study shows that amiodarone subtype selectively downregulates the TR mRNA levels in mouse myocardium in a dose-dependent manner. These results support a thyroid hormone-dependent action of amiodarone.

Efficacy and safety of intravenous amiodarone in recent-onset atrial fibrillation: experience in patients admitted to a general internal medicine department

We examined the efficacy and safety of intravenous amiodarone in 20 unselected patients with recent-onset atrial fibrillation who were admitted to a general internal medicine department during a 6-month period. The treatment protocol included a loading dose of 1200 mg intravenous amiodarone in 24 hours, after which amiodarone treatment was continued orally. Eleven of the 20 patients (55%) converted to sinus rhythm within 48 hours of intravenous amiodarone treatment and were discharged in sinus rhythm, while 9/20 (45%) patients failed to convert during hospitalisation. Six patients (30%) failed to convert to sinus rhythm even after one further month of oral treatment. There was one death and a high frequency (25%) of thrombophlebitis during hospitalisation. The in-hospital non-convertors had a significantly lower ejection fraction and initial low ventricular response rate than the convertors. In conclusion, the acute conversion rate by intravenous amiodarone was at best modest. It is suggested that intravenous amiodarone is probably more effective in patients with rapid recent-onset atrial fibrillation and good left ventricular function.

Presynaptic antisympathetic action of amiodarone and its metabolite desethylamiodarone

Amiodarone has a "reserpine-like" sympatholytic action in the heart. The aims of this study were to test whether desethylamiodarone (DEA), the in vivo bioactive metabolite of amiodarone, has this action and whether this action could be demonstrated in a neuronal preparation. Experiments were performed in intact rats, perfused hearts, or brain synaptosomes treated with DEA and amiodarone, and concentrations of norepinephrine (NE) and dihydroxyphenylglycol (DHPG), the intraneuronal metabolite of NE, were assayed in plasma, coronary effluent, and synaptosomes. In perfused hearts, DEA at 1, 3, and 10 microM increased DHPG overflow by threefold, sixfold, and ninefold, respectively (all p < 0.01 vs. control). DEA at 1 microM was more potent than amiodarone in increasing DHPG overflow. DEA at 1 and 3 microM also inhibited NE release evoked by sympathetic nerve stimulation (p < 0.05). In intact rats, intravenous DEA at 15 mg/kg elicited onefold increase in plasma DHPG level, and oral pretreatment with amiodarone did not interfere with the sympatholytic action of intravenous amiodarone. In synaptosomes, 40-min incubation with amiodarone, DEA (both 10 microM), and reserpine reduced synaptosomal NE content by 42, 45, and 60%, respectively. Thus similar to its parent drug, DEA exerts a presynaptic sympatholytic action in rat hearts in vivo and in vitro. This action of amiodarone and DEA also was observed in synaptosomes.

Effects of amiodarone on the P-wave triggered signal-averaged electrocardiogram in patients with paroxysmal atrial fibrillation and coronary artery disease

The effects of a 6-week treatment with amiodarone on the P-wave triggered signal-averaged electrocardiogram in patients with paroxysmal atrial fibrillation and coronary artery disease have been studied. Amiodarone favorably influences P-wave triggered signal-averaged electrocardiographic parameters, predominantly in patients in whom amiodarone is effective in preventing paroxysmal atrial fibrillation.

Effects of amiodarone and its active metabolite desethylamiodarone on the ventricular defibrillation threshold

OBJECTIVES

We evaluated whether the reported difference in the ventricular defibrillation threshold (DFT) between short-term intravenous and oral amiodarone is due to the effect of amiodarone's active metabolite desethylamiodarone (DEA).

BACKGROUND

Amiodarone is frequently used in patients with implantable cardioverter-defibrillator devices (ICD). Long-term oral amiodarone raises the DFT, but intravenous amiodarone has not been shown to have this effect. DEA, an active metabolite of amiodarone, has different electrophysiologic properties than its parent compound and may be responsible for the observed different effects of intravenous and oral amiodarone on DFT.

METHODS

We ascertained the DFT in 24 pigs randomized to receive intravenous amiodarone, DEA or vehicle. Defibrillation was delivered through a transvenous lead system using a biphasic waveform. The DFT was determined using an up-down DFT algorithm and defined as the average minimal energies resulting in successful defibrillation delivered from ascending and descending serial shocks.

RESULTS

Amiodarone caused a dose-response increase in DFT (mean +/- SD) from 22.7 +/- 4.1 (baseline) to 26.1 +/- 2.9 (10 mg/kg body weight), p = 0.11, to 34.9 +/- 8.2 J (after an additional 15 mg/kg), p = 0.035. DEA (10 mg/kg) caused an increase in DFT from 20.5 +/- 6.3 to 33.9 +/- 13.6 J, p < 0.01. Addition of 15 mg/kg of DEA resulted in hemodynamic instability and thus DFT was not obtained. In the control group, DFT decreased from 26.8 +/- 7.7 at baseline to 23.1 +/- 7.4 (dose 1), p = 0.19, to 22.8 +/- 6.2 J (dose 2), p = 0.18.

CONCLUSIONS

DEA increases DFT by a greater amount than its parent drug amiodarone. There is an effect of intravenous amiodarone on DFT that is dose dependent.

Differential effects of D-sotalol, quinidine, and amiodarone on dispersion of ventricular repolarization in the isolated rabbit heart

INTRODUCTION

Increased dispersion of ventricular repolarization has been suggested as a cause of proarrhythmic effects of Class IA or III antiarrhythmic drugs, such as d-sotalol, quinidine, and amiodarone.

METHODS AND RESULTS

The influence of d-sotalol, quinidine, and amiodarone on the dispersion of monophasic action potential (MAP) durations was studied in 55 isolated Langendorff-perfused rabbit hearts at different pacing cycle lengths (CLs). MAP duration measured at 90% repolarization (APD90) was determined from 6 to 8 endocardial and epicardial MAP recordings with dispersion of ventricular repolarization defined as the range of APD90. The protocol was repeated 60 minutes after initiation of a perfusate containing increasing concentrations of d-sotalol (n = 12, 10[-6] M, 10[-5] M, and 5 x 10[-5] M) and quinidine (n = 8, 10[-6] M and 10[-5] M). Seventeen rabbits were fed with an aqueous solution of amiodarone (50 mg/kg per day over 4 weeks). The data of these experiments (n = 17) were compared with a series of 18 untreated control rabbits. Dispersion of ventricular repolarization was unchanged with the low concentration of d-sotalol (10[-6] M) but was increased-particularly at long CLs-with higher d-sotalol concentrations. With both concentrations of quinidine, dispersion of ventricular repolarization was increased in a rate-independent manner. Amiodarone did not affect dispersion of ventricular repolarization.

CONCLUSIONS

Rate-dependent and concentration-dependent increases in dispersion of ventricular repolarization by d-sotalol and quinidine in this isolated rabbit heart model may help explain their proarrhythmic effects while the absence of an increase in dispersion of ventricular repolarization with amiodarone correlates with its clinically observed lower incidence of proarrhythmia.

Circadian variation of sustained ventricular tachycardia in patients subject to standard adrenergic blockade

Morning peaks in the circadian variation of sustained ventricular tachycardia (VT) may reflect the contribution of sympathetic activation to onset of VT. We hypothesized that adrenergic blockade would eliminate this morning peak. Fifty-four patients using a defibrillator had 1114 time-stamped episodes of VT requiring therapy with a device: 1012 episodes with and 102 episodes without antiadrenergic medications. Nine patients had episodes both with and without antiadrenergic medication and were examined separately. In patients taking antiadrenergic agents, data fitted to a harmonic regression model revealed a morning peak at 9:00 AM (R2= 0.542; p < 0.05), with a secondary peak at 4 PM. Those not receiving antiadrenergic therapy had a similar morning peak. Antiadrenergic agents as used in standard clinical practice do not prevent circadian variation in onset of VT. This variation may be mediated by systems other than adrenergic receptor-linked activation or may reflect inadequacy of adrenergic blockade in standard clinical dosing.

Population pharmacokinetics of intravenous amiodarone and comparison with two-stage pharmacokinetic analysis

The disposition of amiodarone, an antiarrhythmic agent was evaluated after a single intravenous infusion (5 mg/kg over 15 minutes) in patients of various ages and with various degrees of renal function and left ventricular function. The plasma concentration-time data were obtained from three clinical studies with similar protocols. The data were analyzed by nonlinear mixed-effects modeling (NONMEM) to estimate the population pharmacokinetic parameters of amiodarone and to determine the significant demographic covariates affecting these parameters. The pharmacokinetic parameters of amiodarone (weight-corrected) also were calculated using two-stage analysis and were compared with the results obtained from the mixed-effects analysis. The population plasma concentration-time profile of amiodarone was best described by a four-compartment model. Demographic covariates (i.e., creatinine clearance and ejection fraction) did not improve the final pharmacostatistical model significantly. The results from the two-stage analysis showed no significant relationship between amiodarone pharmacokinetic parameters and age, gender, renal function, or ejection fraction. The results from one study, however, demonstrated that advanced age (> or = 65 years) resulted in reduced amiodarone clearance coupled with a prolonged elimination half-life. No such correlation was detected with NONMEM analysis, which may be partly attributable to the small number of elderly patients. Overall, the results from NONMEM analysis validated the results obtained from the two-stage analysis.

Amiodarone: the expanding antiarrhythmic role and how to follow a patient on chronic therapy

Amiodarone was introduced as an antiarrhythmic compound in the early 1970s and was approved in the U.S. for the treatment of refractory ventricular arrhythmias in late 1984. Since that time the drug has become the most widely studied antiarrhythmic compound with expanding potential indications, including maintaining stability of sinus rhythm, secondary prevention in the survivors of myocardial infarction, and prolongation of survival in certain subsets of patients with congestive heart failure. Intravenous amiodarone was introduced in the U.S. in 1995 for the control of recurrent destabilizing ventricular tachycardia or ventricular fibrillation resistant to conventional therapy. The level of comfort in its use has risen considerably in the recent past. This has stemmed from the reasonably decisive evidence that class I agents increase mortality in patients with structural heart disease. In contrast, amiodarone either reduces mortality or its effect is neutral; this is consistent with its low to negligible proarrhythmic actions. The drug does not aggravate heart failure and it may even increase left ventricular ejection fraction and improve exercise capacity. Above all, it is becoming increasingly evident from wider experience and from controlled clinical trials that the side-effect profile of the drug is not as compelling an issue as it appeared to be when first used in much higher doses. Therefore, the overall objective of amiodarone therapy is to use the lowest dose that produces a defined therapeutic end point without causing serious side effects. Careful clinical surveillance in conjunction with monitoring of certain laboratory parameters and indices of efficacy at regular intervals permits the drug to be used effectively in a large number of patients who fail to respond to, or are intolerant of other antiarrhythmic compounds. Many experienced clinicians have begun to consider the use of amiodarone as first-line therapy in certain disorders of rhythm, especially in patients with severely compromised ventricular function.

Amiodarone therapy in chronic heart failure and myocardial infarction: a review of the mortality trials with special attention to STAT-CHF and the GESICA trials. Grupo de Estudio de la Sobrevida en la Insuficiencia Cardiaca en Argentina

Amiodarone appears to reduce sudden death in patients with left ventricular dysfunction resulting from an acute MI or a primary dilated cardiomyopathy, particularly if complex ventricular arrhythmias are present. Amiodarone's beneficial effect on mortality in these patients could be unrelated to its antiarrhythmic effects. Multiple factors could account for the improvement in mortality such as the drug's antiischemic effects, neuromodulating effects, its effect on left ventricular function and on heart rate. Moreover, patients with LV dysfunction who have survived an episode of sudden death would potentially benefit from amiodarone therapy. Future trials are needed to determine the precise subsets(s) of patients who would benefit from the drug and the most efficacious dosing regimen for the drug. Based on available data, amiodarone is the only antiarrhythmic agent which has not been shown to increase mortality in patients with chronic heart failure.

Nonsustained polymorphous ventricular tachycardia during amiodarone therapy for atrial fibrillation complicating cardiomyopathy. Management with intravenous magnesium sulfate

A case is presented in which amiodarone was administered to suppress paroxysmal atrial fibrillation in a patient with an idiopathic cardiomyopathy. Eleven days after initiation of therapy with amiodarone, the patient experienced syncope and was noted to have recurrent episodes of polymorphous ventricular tachycardia. The patient was hospitalized and treated with a bolus as well as continuous infusion of intravenous magnesium sulfate. When the infusion was transiently discontinued, recurrences of polymorphous ventricular tachycardia were noted. The probable proarrhythmic action of amiodarone, although rare, is reviewed along with a discussion of the novel use of intravenous magnesium sulfate therapy.

Intravenous amiodarone

Intravenous amiodarone was approved in 1995 for the treatment of malignant and resistant ventricular arrhythmia. Although it is an "old drug," much has been learned recently about this complex drug and its application in a variety of cardiac arrhythmias. The objectives of this review were to summarize what is known about intravenous amiodarone, including its pharmacologic and electrophysiologic effects, to review its efficacy for the treatment of patients with highly malignant ventricular arrhythmia and to provide specific information about its clinical use for this and other indications. The studies that were reviewed were selected on the basis of time published (from 1983 to 1995) and the completeness of information provided regarding patient clinical characteristics, drug dosing and methods of evaluation, efficacy analyses, long-term follow-up and complications. The full data from the three controlled trials that formed the basis of the drug's approval are contained in published reports that were also extensively reviewed. Intravenous amiodarone has demonstrable efficacy for the treatment of frequently recurrent destabilizing ventricular tachycardia and ventricular fibrillation, with suppression rates of 63% to 91% in uncontrolled trials. The three pivotal trials confirmed these findings and demonstrated a dose-response relation, with at least comparable efficacy to bretylium, a drug with a similar indication. The safety profile has also been well described; cardiovascular adverse effects are the most frequent, especially hypotension. Intravenous amiodarone is a useful addition to the drugs available for the treatment of patients with very severe ventricular arrhythmia. Its use in patients with other rhythm disorders appears promising, but final recommendations must await development of definitive data from ongoing clinical trials.

Efficacy, safety, and determinants of conversion of atrial fibrillation and flutter with oral amiodarone

Amiodarone is effective for long-term maintenance of sinus rhythm after electrical cardioversion of refractory atrial fibrillation or flutter. To examine its efficacy and safety for pharmacologic conversion of these arrhythmias, we studied 129 patients with refractory atrial fibrillation or flutter who had failed previous intensive conventional antiarrhythmic treatment. In anticipation of electrical cardioversion, patients were loaded with amiodarone, 600 mg/day during a 4-week period. The main outcome measure was pharmacologic conversion during this period. During the loading period, 23 patients (18%) converted to sinus rhythm. When analyzed in a multivariate model, conversion was related to desethylamiodarone plasma level (p = 0.0006), arrhythmia duration (p = 0.04), left atrial area (p = 0.02), and concomitant treatment with verapamil (p = 0.01). During ongoing atrial fibrillation after loading, the ventricular rate decreased from 100 +/- 25 to 87 +/- 27 beats/ min (p <0.001). Amiodarone appeared to be safe and did not have to be discontinued because of intolerable side effects. Thus, amiodarone loading is safe and is still able to convert refractory atrial fibrillation or flutter. Conversion is related to increased desethylamiodarone plasma levels and concomitant treatment with verapamil. Because prolonged loading may increase desethylamiodarone plasma concentrations, this may enhance efficacy and obviate the need for electrical cardioversion.