Intravenous amiodarone: pharmacology, pharmacokinetics, and clinical use

Junctional Ectopic Tachycardia Caused by Junctophilin-2 Expression Silencing Is Selectively Sensitive to Ryanodine Receptor Blockade

Junctional ectopic tachycardia (JET) is a potentially fatal cardiac arrhythmia. Hcn4:shJph2 mice serve as a model of nodal arrhythmias driven by ryanodine type 2 receptor (RyR2)-mediated Ca2+ leak. EL20 is a small molecule that blocks RyR2 Ca2+ leak. In a novel in vivo model of JET, Hcn4:shJph2 mice demonstrated rapid conversion of JET to sinus rhythm with infusion of EL20. Primary atrioventricular nodal cells demonstrated increased Ca2+ transient oscillation frequency and increased RyR2-mediated stored Ca2+ leak which was normalized by EL20. EL20 was found to be rapidly degraded in mouse and human plasma, making it a potential novel therapy for JET.

Control of Heart Rate in Infant and Child Tachyarrhythmia With Reduced Cardiac Function Using Landiolol (HEARTFUL) - Results of a Prospective, Multicenter, Uncontrolled Clinical Study

BACKGROUND

The prospective Control of HEART rate in inFant and child tachyarrhythmia with reduced cardiac function Using Landiolol (HEARTFUL) study investigated the effectiveness and safety of landiolol, a short-acting β₁ selective blocker, in children.Methods and Results: Twenty-five inpatients aged ≥3 months to <15 years who developed supraventricular tachyarrhythmias (atrial fibrillation, atrial flutter, supraventricular tachycardia, and inappropriate sinus tachycardia) were treated with landiolol. The primary endpoint, the percent of patients with a reduction in heart rate ≥20% from the initial rate of tachycardia, or termination of tachycardia at 2 h after starting landiolol, was achieved in 12/25 patients (48.0%; 95% CI 28.4-67.6), which exceeded the predetermined threshold (38.0%). At 2 h after starting landiolol administration, heart rate had decreased by ≥20% in 45.8% (11/24) and recovery to sinus rhythm was achieved in 40.0% (6/15) of the patients. Adverse reactions (ARs) occurred in 24.0% (6/25) of patients, and the study was discontinued in 4.0% (1/25) of the patients; however, none of these ARs were considered serious. The most common AR was hypotension (20.0% [5/25] of patients).

CONCLUSIONS

The HEARTFUL study has demonstrated the efficacy of landiolol, by reducing heart rate or terminating tachycardia, in pediatric patients with supraventricular tachyarrhythmias. Although serious ARs and concerns were not identified in this study, physicians should be always cautious of circulatory collapse due to hypotension.

Management of atrial fibrillation in rheumatic heart disease

Rheumatic heart disease (RHD) is the underlying cause of a significant proportion of atrial fibrillation (AF) in the low- and middle-income countries, while nonvalvular AF is the most common cause of AF in high-income countries. RHD is also common among African Americans, migrants, and the indigenous population of high-income countries. The onset of AF in RHD patients is a clinical marker of worse outcomes and is associated with significant morbidity and mortality. Despite RHD being a major cause of morbidity and mortality in the young in many parts of the world, it is often neglected by policymakers, the media, and even the medical fraternity. Stroke risk assessment using various risk scores has not been systematically evaluated in rheumatic AF patients. Rate control may not be ideal for symptom control in rheumatic AF patients considering the young age and an active lifestyle. There is limited information regarding the nonpharmacological management of rheumatic AF. The current management guidelines based on nonvalvular AF do not apply to rheumatic AF patients who are often younger, are women, and have fewer comorbidities. This review critically looks at specific areas such as stroke prevention with reference to direct oral anticoagulants, cardioversion, rate and rhythm control strategies, and the role of nonpharmacological methods in rheumatic AF management. Future recommendations must be cognizant of local health care systems and resourcing considering the geographic distribution of the disease.

The use of intravenous amiodarone in patients with atrial fibrillation and Wolff-Parkinson-White syndrome

BACKGROUND

It was reported that intravenous amiodarone might induce ventricular fibrillation for acute treatment in patients with atrial fibrillation (AF) and Wolff-Parkinson-White (WPW) syndrome. No study was done to assess its application comprehensively in this population.

METHODS

This study was a retrospective analysis and undertaken by reviewing medical records and electronic databases to search for patients admitted with tachycardia resulting from WPW syndrome and AF, who have intravenously administrated amiodarone at the emergency department from January 2008 to June 2018.

RESULTS

Thirty patients were involved in this study, of which 27 were males. The mean age of the patients was 47.8 ± 17.0 years. The mean systolic blood pressure and diastolic blood pressure were 111.9 ± 18.3 mmHg and 76.1 ± 14.6 mmHg, respectively. The mean heart rate was 171 (150-189) beats per minute. Half of the patients (53.3%) had no comorbidities, and only one had prior syncope. Nearly 17 patients (56.7%) started with a loading dose of 150 mg. No ventricular acceleration or VF developed. The incidence of hypotension was 3.3% (1/30). Eighteen patients (60.0%) restored to sinus rhythm by amiodarone with the conversion time of 486.0 (229.0-1278.0) minutes.

CONCLUSIONS

Intravenous amiodarone might be an alternative for acute treatment of AF and WPW syndrome in patients characterized by stable hemodynamics, relatively low admission heart rate, few comorbidities, elder age, and no prior syncope. The loading dosage of 150 mg appeared to be preferred, and the maintenance period was better to less than 12 hours. Monitoring and electrolyte correction were also necessary. It is essential to keep a defibrillator nearby during pharmacologic cardioversion.

[Clinical aspects of treatment with amiodarone]

Amiodarone has multiple and complex electrophysiological effects that render it a very effective antiarrhythmic drug for the treatment of both, supraventricular and ventricular arrhythmias. Proarrhythmic effects of amiodarone in patients with structural heart disease are rare. However, extracardiac adverse effects occurring in association with amiodarone treatment are frequent and feared. These adverse effects have usually been related to total amiodarone exposure (i. e., dose and duration of treatment). Parallel to a more frequent use of lower amiodarone maintenance doses (100-200 mg/day), the incidence of severe unwanted extracardiac side effects has decreased. High-dose maintenance regiments (daily dose ≥300 mg) are usually obsolete. This paper discusses recommendations regarding the monitoring of cardiac and extracardiac side effects of amiodarone. They need to be regarded by physicians using amiodarone to ensure long-term safety of amiodarone therapy.

A pharmacokinetic model for amiodarone in infants developed from an opportunistic sampling trial and published literature data

Amiodarone is a first-line antiarrhythmic for life-threatening ventricular fibrillation or ventricular tachycardia in children, yet little is known about its pharmacokinetics (PK) in this population. We developed a population PK (PopPK) model using samples collected via an opportunistic study design of children receiving amiodarone per standard of care supplemented by amiodarone PK data from the literature. Both study data and literature data were predominantly from infants < 2 years old, so our analysis was restricted to this group. The final combined dataset consisted of 266 plasma drug concentrations in 45 subjects with a median (interquartile range) postnatal age of 40.1 (11.0-120.4) days and weight of 3.9 (3.1-5.1) kg. Since the median sampling time after the first dose was short (study: 95 h; literature: 72 h) relative to the terminal half-life estimated in adult PopPK studies, values of the deep compartment volume and flow were fixed to literature values. A 3-compartment model best described the data and was validated by visual predictive checks and non-parametric bootstrap analysis. The final model included body weight as a covariate on all volumes and on both inter-compartmental and elimination clearances. The empiric Bayesian estimates for clearance (CL), volume of distribution at steady state, and terminal half-life were 0.25 (90% CL 0.14-0.36) L/kg/h, 93 (68-174) L/kg, and 266 (197-477) h, respectively. These studies will provide useful information for future PopPK studies of amiodarone in infants and children that could improve dosage regimens.

High-resolution sub-cellular imaging by correlative NanoSIMS and electron microscopy of amiodarone internalisation by lung macrophages as evidence for drug-induced phospholipidosis

Correlative NanoSIMS and EM imaging of amiodarone-treated macrophages shows the internalisation of the drug at a sub-cellular level and reveals its accumulation within the lysosomes, providing direct evidence for amiodarone-induced phospholipidosis. Chemical fixation using tannic acid effectively seals cellular membranes aiding intracellular retention of diffusible drugs.

Therapeutic monitoring of amiodarone: pharmacokinetics and evaluation of the relationship between effect and dose/concentration

Amiodarone is the most effective agent in the therapy of arrhythmias. However, the clinical effect of acute and chronic treatment is unclear and there are differences irrespective of comparable plasma/myocardial amiodarone and its metabolite desethylamiodarone concentations as well. Its unusual pharmacokinetics results in interindividual variation in plasma levels. The association between amiodarone and desethylamiodarone plasma levels and clinical efficacy is difficult to evaluate. This review was carried out to assess whether there is any objective correlation between amiodarone and desethylamiodarone plasma levels and the clinical effect. We summarized the results of relevant studies and clarified the relationship between plasma levels and effect vis á vis the pharmacokinetics and pharmacogenetics of this drug. Certain correlation was seen with oral amiodarone therapy, in others, plasma amiodarone levels were unrelated to therapeutic response and showed no correlation with changes in electrocardiogram or electrophysiological parametres. Several studies show that plasma concentration ranging between 0.5 and 2.5 mg/L appears to be the most effective, others demonstrate no difference between responders and non-responders. One way of interpreting plasma levels is to establish an individual patient´s effective concentration. Therapeutic drug monitoring can contribute to determining optimal concentration.

Will There Be a Cure for Ebola?

Despite the unprecedented Ebola virus outbreak response in West Africa, no Ebola medical countermeasures have been approved by the US Food and Drug Administration. However, multiple valuable lessons have been learned about the conduct of clinical research in a resource-poor, high risk-pathogen setting. Numerous therapeutics were explored or developed during the outbreak, including repurposed drugs, nucleoside and nucleotide analogues (BCX4430, brincidofovir, favipiravir, and GS-5734), nucleic acid-based drugs (TKM-Ebola and AVI-7537), and immunotherapeutics (convalescent plasma and ZMapp). We review Ebola therapeutics progress in the aftermath of the West Africa Ebola virus outbreak and attempt to offer a glimpse of a path forward.

Amiodarone Treatment of Junctional Ectopic Tachycardia in a Neonate Receiving Extracorporeal Membrane Oxygenation

Objective:

To describe the administration of amiodarone and the resulting serum concentrations in a neonate receiving extracorporeal membrane oxygenation (ECMO).

Case Summary:

A 3463 g, 38 week gestational age male diagnosed with tetralogy of Fallot developed junctional ectopic tachycardia (JET) and required ECMO support following cardiac surgery. The patient continued to show JET despite cooling, pacing, and intravenous amiodarone infusion, with the dose initiated at 10 μg/kg/min. Sinus rhythm was achieved following 5 days of treatment, additional amiodarone boluses, and an increase in the infusion rate to 20 μg/kg/min. Two serum concentrations of amiodarone were obtained during therapy. On day 4, the concentration was 0.9 mg/L at the 20 μg/kg/min infusion rate; a bolus dose of 5 mg/kg was administered 1 hour later. The serum concentration the following day, with the infusion rate unchanged, was 2 mg/L.

Discussion:

ECMO is used increasingly postoperatively in patients with congenital cardiac abnormalities. The incidence of JET following repair of tetralogy of Fallot is 22%. Despite the minimal information on the pharmacokinetics of amiodarone in neonates, it has been used in doses up to 20 μg/kg/min for the treatment of postoperative JET. As of August 25, 2006, we found no reports describing its dosage and use in patients undergoing ECMO.

Conclusions:

The delivery of amiodarone to a patient receiving ECMO may be complicated by the administration of large blood volumes, circuit changes, and binding to the circuit. Neonates receiving ECMO may require larger amiodarone doses to achieve a therapeutic effect. Further investigation is required to define the pharmacokinetics and pharmacodynamics of amiodarone in neonates receiving ECMO.

Cardiac Dysrhythmias during Donor Care

Organ procurement coordinators must treat various cardiac dysrhythmias (arrhythmias), including rhythm disturbances that may cause or follow a cardiac arrest, in about 15% to 50% of donors. Treatment decisions should be based on the particular dysrhythmia and its effect on donor blood pressure. Medications selected should be effective but short acting. In this article, data available in publications located through a PubMed search are reviewed and specific dysrhythmias that are likely to occur during donor care are described. Treatment recommendations are based on guidelines from the American Heart Association.

Comparison of oral and intravenous alfacalcidol in chronic hemodialysis patients

Background

Activated vitamin D is the mainstay of treatment for secondary hyperparathyroidism (SHPT) in chronic hemodialysis patients. However, the optimal route of administration is still debated. The aim of our study was to compare efficacy of oral vs intravenous (IV) administration of alfacalcidol in hemodialysis. A secondary objective was to determine the cost-effectiveness advantage of oral administration.

Methods

Eighty-eight chronic hemodialysis patients receiving IV alfacalcidol three times a week were included in the study. All were switched to the same dose of alfacalcidol given orally three times a week during the hemodialysis session. A budget impact analysis was performed.

Results

Mean patient age was 64 years old and 43% were males. The mean alfacalcidol dose administered was 2.1 μg three times a week. After three months, serum parathormone (PTH) levels decreased from 80 to 59 pmol/L (p = 0.001) and total serum calcium levels increased from 2.34 to 2.40 mmol/L (p = 0.002). After six months, total serum calcium levels were still significantly higher. Alfacalcidol dosage was significantly decreased during study period; the mean reduction was 0.44 μg per dose. Finally, oral administration was associated with an annual cost reduction of 197 678$CAN and an annual nursing time reduction of 25 days.

Conclusion

Our findings support that switching IV to oral administration of alfacalcidol during hemodialysis sessions may lead to a similar control of SHPT with lower doses of activated vitamin D. This is a good strategy for optimizing compliance and may allow a dose reduction because of a greater efficacy to suppress PTH. Oral administration also has significant cost-effectiveness advantages.

Intravenous amiodarone for acute pharmacological conversion of atrial fibrillation in the emergency department

Atrial fibrillation (AF) is the most common arrhythmia seen in patients presenting to the emergency department (ED). Pharmacological conversion of atrial fibrillation to normal sinus rhythm (NSR) may be a feasible management strategy in selected patients. Recent guidelines have recommended intravenous amiodarone, a class III antiarrhythmic agent, for the conversion of AF to NSR. The purpose of this review is to examine the published evidence for the efficacy of IV amiodarone for the acute conversion of AF to NSR in the ED. Currently available data from 11 randomized, controlled trials and 3 meta analyses do not support the use of conventional doses of IV amiodarone for acute conversion in the ED. High dose IV or combined IV and oral administration may be effective as early as 8 hours in patients with recent-onset AF of <48 hour duration in patients without contraindications to these high dose regimens. There are no data to support the use of IV amiodarone for acute conversion in patients with an ejection fraction of <40% or clinical heart failure, so its use in these scenarios should be limited to symptomatic patients who are refractory to electrical conversion. More well-designed studies are required to determine the role of IV amiodarone for the acute conversion of AF in the ED.

The association between insulin-like growth factor-I and cardiac repolarization

OBJECTIVE

Previous studies reported associations between insulin-like growth factor I (IGF-I) serum concentration and cardiac morbidity and mortality, but the association between IGF-I serum concentration and cardiac repolarization has not been investigated in a population-based study so far. Therefore, we analyzed the impact of IGF-I concentrations on QTc, QT and RR intervals in two population based studies, The Study of Health in Pomerania (SHIP) and the Rotterdam Study.

DESIGN

457 individuals from SHIP and 155 individuals from the Rotterdam Study older than 55 years and without cardiovascular diseases and a left ventricular hypertrophy were investigated. IGF-I was determined by automated two-site chemiluminescence immunoassays and electrocardiograms were recorded by an ACTA electrocardiograph at a sampling frequency of 500 Hz. The association of IGF-I with QTc, QT and RR intervals was investigated by multivariable linear regression analyses adjusted for age, gender, diabetes mellitus, myocardial infarction, hypertension, body mass index, serum potassium and calcium in both studies separately and in pooled analysis.

RESULTS

There were no significant associations between log-transformed IGF-I and QTc interval in the single populations, whereas a significant inverse association was detectable in the pooled population (β, -15.6; 95%-confidence interval, -25.7, -5.5). The QTc interval was significantly higher in the first tertile of IGF-I compared to the third tertile (β, 5.4; 95%-confidence interval, 9.5-1.3) in the pooled analysis.

CONCLUSION

The inverse association between IGF-I serum concentrations and QTc interval in our study is suggestive of a higher risk for cardiac arrhythmias and thus might provide additional evidence for increased cardiovascular mortality in subjects with low IGF-I secretion.

Amiodarone for the emergency care of children

Amiodarone is a class 3 antiarrhythmic agent used for a broad range of arrhythmias including adenosine-resistant supraventricular tachycardia, junctional ectopic tachycardia, and ventricular tachycardia. Compared with adults, there are few data on its use in children with arrhythmias resistant to conventional therapy. National and international guidelines for cardiopulmonary resuscitation and emergency cardiovascular care recommend its use for a variety of arrhythmias based on case reports, cohort studies, and extrapolation from adult data. This article will review the historical development, chemical properties, metabolism, indications and contraindications, and adverse effects of amiodarone in infants and children. After completing this CME activity, the reader should be able to utilize amiodarone in the pediatric population for arrhythmias and identify complications associated with its use.

Dronedarone: Emergence of a New Therapeutic Option for the Treatment of Atrial Fibrillation

This continuing feature updates readers on recent developments in cardiovascular pharmacotherapy. Cardiovascular disease remains the number 1 killer in the United States, and more clinical outcome trials have been conducted in cardiology than in any other field of medicine. Given this rapidly expanding knowledge base, if pharmacists stay current with developments in drug therapy, they can have a significant impact on prevention and treatment.

Amiodarone Prophylaxis: Impact on Atrial Fibrillation and Outcomes after Cardiac Surgery

This continuing feature will update readers on recent developments in cardiovascular pharmacotherapy. Cardiovascular disease remains the number one killer in the United States, and more clinical outcome trials have been conducted in cardiology than in any other field of medicine. Given this rapidly expanding knowledge base, pharmacists can have a significant impact on prevention and treatment—if they keep current with developments in drug therapy.

Intravenous and oral administration of amiodarone for the treatment of recent onset atrial fibrillation after digoxin administration

BACKGROUND

Atrial fibrillation (AF) remains a significant contributor to cardiovascular morbidity. Amiodarone is a potent antiarrhythmic drug. The safety and efficacy of oral versus intravenous (i.v.) Amiodarone in the treatment of AF of recent onset (duration <48 h) was investigated.

METHODS

The study population consisted of 223 patients with symptomatic AF, of whom 110 received 600 mg oral Amiodarone (Group A) in three divided doses and 113 received i.v. Amiodarone (5 mg/kg over 30 min followed by 1000 mg over the next 24 h) (Group B). Digoxin was administered to all patients, who had not previously received it. All patients were monitored for 24 h.

RESULTS

Conversion to sinus rhythm occurred in 85.45% of group A and 82.30% in group B (p=NS). Mean time of cardioversion in group A was 20+/-4.5 h and in group B was 12+/-8 h (p<0,001). However, blood pressure (BP) in group A remained stable for the observation period, whereas it fell significantly in group B. Treatment was not discontinued in any of the patients in either group, however 13 patients in group B developed superficial phlebitis.

CONCLUSIONS

Both forms of the drug are extremely efficient in restoring sinus rhythm in AF of recent onset, although the i.v. form acts quicker. The oral form of the drug does not alter significantly the patients' BP.

Intravenous amiodarone treatment in horses with chronic atrial fibrillation

Six horses without underlying cardiac disease were presented because of atrial fibrillation of between 5 and 12 months duration. These horses received an intravenous amiodarone treatment of 5mg/kg/h for 1 h followed by 0.83mg/kg/h for 23h and subsequently 1.9mg/kg/h for 30h. During treatment, clinical signs were monitored and a surface ECG and an intra-atrial electrogram were recorded. Infusion was discontinued when sinus rhythm or side effects occurred. Four horses successfully cardioverted, of which one showed symptoms of hind limb weakness and weight shifting. Two horses did not cardiovert and showed similar side effects. In all horses, side effects disappeared within 6h after termination of treatment. Cardiac side effects, such as pro-arrhythmia, were not seen in any of the horses. Total bilirubin slightly increased in three horses and normalised within four days. It was concluded that amiodarone has the potential to treat naturally occurring chronic atrial fibrillation in horses, although further research is needed to refine the infusion protocol.

Evaluation of the pharmacokinetics and bioavailability of intravenously and orally administered amiodarone in horses

OBJECTIVE

To determine the clinical effects and pharmacokinetics of amiodarone after single doses of 5 mg/kg administered orally or intravenously.

ANIMALS

6 healthy adult horses.

PROCEDURE

In a cross over study, clinical signs and electrocardiographic variables were monitored and plasma and urine samples were collected. A liquid chromatography-mass spectrometry method was used to determine the percentage of protein binding and to measure plasma and urine concentrations of amiodarone and the active metabolite desethylamiodarone.

RESULTS

No adverse clinical signs were observed. After IV administration, median terminal elimination half-lives of amiodarone and desethylamiodarone were 51.1 and 75.3 hours, respectively. Clearance was 0.35 L/kg x h, and the apparent volume of distribution for amiodarone was 31.1 L/kg. The peak plasma desethylamiodarone concentration of 0.08 microg/mL was attained 2.7 hours after IV administration. Neither parent drug nor metabolite was detected in urine, and protein binding of amiodarone was 96%. After oral administration of amiodarone, absorption of amiodarone was slow and variable; bioavailability ranged from 6.0% to 33.7%. The peak plasma amiodarone concentration of 0.14 microg/mL was attained 7.0 hours after oral administration and the peak plasma desethylamiodarone concentration of 0.03 microg/mL was attained 8.0 hours after administration. Median elimination half-lives of amiodarone and desethylamiodarone were 24.1 and 58.6 hours, respectively.

CONCLUSION AND CLINICAL RELEVANCE

Results indicate that the pharmacokinetic distribution of amiodarone is multicompartmental. This information is useful for determining treatment regimens for horses with arrythmias. Amiodarone has low bioavailability after oral administration, does not undergo renal excretion, and is highly protein-bound in horses.

Intravenous amiodarone for conversion of atrial fibrillation: misled by meta-analysis?

Therapeutic goals for atrial fibrillation (AF) include ventricular rate control, stroke prevention, conversion to normal sinus rhythm, and maintenance of normal sinus rhythm. The optimal strategy of rate versus rhythm control for acute management of patients with AF is a continuing debate. However, selected patients may require acute treatment with antiarrhythmic agents for conversion of symptomatic AF episodes to normal sinus rhythm. Recently published randomized controlled trials, qualitative systematic reviews, meta-analyses, and evidence-based international consensus guidelines have addressed the controversy regarding acute conversion of AF using antiarrhythmic therapy. Although meta-analyses often provide the highest level of evidence, the validity and application of their results are based on the quality of their methodology and accuracy of reporting. Authors of the most recent meta-analysis of amiodarone for conversion of AF state that the drug is effective and relatively rapid acting in converting AF to normal sinus rhythm in a wide range of patients, and they recommend it as a first-line drug. We feel that these conclusions are overstated and potentially misleading due to methodologic limitations of the analysis. The results of this meta-analysis and others concerning acute conversion of AF should be viewed as hypothesis generating and not the definitive answer to this question. Ultimately, well-designed, adequately powered, randomized placebo- or rate-controlled trials are needed in specific patient populations with AF to determine the absolute benefit of intravenous amiodarone for conversion of AF to normal sinus rhythm. Until more data are available, intravenous amiodarone cannot be promoted as a first-line agent for this purpose.

Dosing of medications in morbidly obese patients in the intensive care unit setting

OBJECTIVE

To derive recommendations for the dosing of commonly used medications in the morbidly obese patient in the ICU.

DATA SOURCES

Articles were obtained through computerized searches involving MEDLINE. The bibliographies of retrieved publications and textbooks were reviewed for additional references.

STUDY SELECTION

All studies involving the pharmacokinetics or pharmacodynamics of medications in obese subjects or patients.

DATA EXTRACTION

The emphasis was on studies involving morbidly obese patients but, in the absence of such data, investigations involving lesser forms of obesity were extracted.

DATA SYNTHESIS

There is a paucity of data upon which to make recommendations for dosing commonly used medications in the morbidly obese patient in the ICU, although recommendations were provided based on the available information.

CONCLUSIONS

There is clearly a need for more investigations involving dosing regimens of medications in the morbidly obese population. Until such studies are available, the clinician must try to derive the best dosing regimens for medications based on the limited pharmacokinetic data available for some agents and clinical judgement.

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.

Dosing of medications in morbidly obese patients in the intensive care unit setting

OBJECTIVE

To derive recommendations for the dosing of commonly used medications in the morbidly obese patient in the ICU.

DATA SOURCES

Articles were obtained through computerized searches involving MEDLINE. The bibliographies of retrieved publications and textbooks were reviewed for additional references.

STUDY SELECTION

All studies involving the pharmacokinetics or pharmacodynamics of medications in obese subjects or patients.

DATA EXTRACTION

The emphasis was on studies involving morbidly obese patients but, in the absence of such data, investigations involving lesser forms of obesity were extracted.

DATA SYNTHESIS

There is a paucity of data upon which to make recommendations for dosing commonly used medications in the morbidly obese patient in the ICU, although recommendations were provided based on the available information.

CONCLUSIONS

There is clearly a need for more investigations involving dosing regimens of medications in the morbidly obese population. Until such studies are available, the clinician must try to derive the best dosing regimens for medications based on the limited pharmacokinetic data available for some agents and clinical judgement.

Amiodarone in the new AHA guidelines for ventricular tachyarrhythmias

OBJECTIVE

To delineate amiodarone's role in the new American Heart Association guidelines for ventricular tachyarrhythmias, review the literature that supports the use of amiodarone in ventricular tachyarrhythmias, describe the pharmaceutical properties of amiodarone and elucidate their clinical implications, and discuss the dosing, preparation, and administration of amiodarone.

DATA SOURCES

A search of MEDLINE (1966-October 2000) database and EMBASE Drugs and Pharmacology database (1980-October 2000) was performed. References from published articles and tertiary references were used to gather additional data.

DATA EXTRACTION

All articles were screened, and pertinent studies were identified and evaluated.

DATA SYNTHESIS

Recent trials have demonstrated amiodarone's usefulness in the setting of ventricular tachyarrhythmias. Based on these investigations and contrary to past guidelines, amiodarone is included in the 2000 advanced cardiovascular life support guidelines as a possible agent for hemodynamically stable monomorphic ventricular tachycardia (VT), non-QT prolonged polymorphic VT, and ventricular fibrillation (VF)/pulseless VT. Although not specifically evaluated in the setting of hemodynamically stable monomorphic VT and non-QT prolonged polymorphic VT, investigations by the intravenous Amiodarone Multicenter Trial Group and other clinical trials make amiodarone an acceptable choice for these arrythmia categories. The results of the ARREST (Resuscitation of Refractory Sustained Ventricular Tachyarrhythmias) trial prove amiodarone to be the antiarrhythmic of choice for VF/pulseless VT.

CONCLUSIONS

Amiodarone is classified as a IIb therapeutic intervention for all three arrhythmia categories, which makes it an acceptable, safe, and useful agent with fair to good evidence to support its use. In addition, amiodarone requires careful preparation and delivery to achieve safe and effective outcomes.

Innovative pharmacologic approaches to cardiopulmonary resuscitation

The survival rate of patients undergoing cardiopulmonary resuscitation is 5 to 15%. New cardiopulmonary resuscitation treatment approaches under investigation include the use of vasopressin as a vasopressor, amiodarone for the treatment of ventricular tachyarrhythmias, and adenosine antagonists (i.e., theophylline) for bradyasystolic rhythms. More innovative approaches include the use of thyroid hormone and endothelin.

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.

A comparison of the antifibrillatory effects of desethylamiodarone to amiodarone in a swine model

We evaluated the effect of two different doses of desethylamiodarone (DEA) and amiodarone on the ventricular fibrillation threshold (VFT). We ascertained the VFT in 24 pigs randomized to intravenous DEA, amiodarone, or vehicle. Ventricular fibrillation was induced by pacing the right ventricle by using a primary drive train at a cycle length of 270 ms for eight beats of 2-ms duration each. A secondary train of 20 pulses of 4-ms duration (100 Hz) immediately followed this over a total duration of 200 ms synchronized to the primary drive train. The intensity of the secondary train stimuli current was initially 2 mA and was increased by 2-mA increments until sustained VF with hemodynamic collapse was induced. The minimal current strength needed to induce sustained VF was defined as the VFT measured in mA. DEA (10 mg/kg) increased the VFT significantly over baseline from 13.5+/-4.9 to 23.2+/-8.8 mA (p = 0.0076). Amiodarone, 10 mg/kg, increased the VFT significantly over baseline (mean +/- SD) from 14.4+/-3.6 to 23.8+/-6.1 mA (p = 0.0016). An additional dose of amiodarone (15 mg/kg) increased the VFT to 38.5+/-15.9 mA, which is significantly greater than the VFT derived from lower-dose amiodarone (p = 0.046). We showed that DEA (10 mg/kg) has a similar antifibrillatory effect as 10 mg/kg of amiodarone. We also demonstrated a dose-dependent effect on VFT for amiodarone.

The effect of amiodarone on the ventricular fibrillation threshold

We evaluated the antifibrillatory effect of two different doses of amiodarone after cardiac arrest with a cardiopulmonary resuscitation (CPR) model in 19 pigs. Ventricular fibrillation was induced by pacing the right ventricle using a primary drive train at a cycle length of 270 msec for 8 beats. The minimum current strength necessary to induce sustained ventricular fibrillation was defined as the ventricular fibrillation threshold (VFT) measured in mA. Three VFT determinations were made at baseline, followed by 9 minutes of continuous CPR with two determinations of VFT, and three after stabilization. The pigs were placed into one of three groups: amiodarone 2 or 5 mg/kg, or placebo. The average poststabilization VFT in each group was compared with the average baseline VFT. Pigs receiving amiodarone 2 mg/kg had significantly higher VFT after stabilization than at baseline (22.88+/-12.76 to 27.10+/-10.18 mA, p=0.048), as did those receiving 5 mg/kg (17.03+/-7.01 to 28.08+/-11.58 mA, p=0.002). The deltaVFT was significantly greater with amiodarone 5 mg/kg than with vehicle (placebo), but not with 2 mg/kg. There were no changes in VFT in any group during CPR versus baseline. When active treatments were combined, the trend was toward better survival in the amiodarone groups (13/13) compared with the placebo group (4/6, p=0.076).

Adverse effects of amiodarone

Amiodarone was introduced 30 years ago as an antianginal agent and subsequently has been used as an antiarrhythmic agent. This drug was initially used for patients with malignant ventricular arrhythmias; however, currently it is being used broadly for rate and rhythm control in patients with atrial fibrillation. At first, amiodarone was primarily used by cardiologists and today it is used throughout the medical profession. Amiodarone therapy can potentially result in a wide range of adverse effects. The majority of these adverse effects are dose related and reversible. The following is a review of the adverse effects and drug interactions of amiodarone along with recommendations for identification and management of these adverse effects.