Amiodarone In Plasma Research Articles

Development, validation and long-term evaluation of a liquid chromatography-tandem mass spectrometry method for simultaneous quantification of amiodarone, desethylamiodarone and mexiletine in human plasma and serum

Amiodarone and mexiletine are used for ventricular arrhythmias, for which a combination therapy of both anti-arrhythmic drugs (AADs) is not uncommon. Therapeutic drug monitoring (TDM) can be beneficial for clinical guidance of therapy, especially to correctly identify adverse events. Desethylamiodarone, the active metabolite of amiodarone, accumulates over time and is associated with serious adverse events. Therefore, simultaneous TDM for amiodarone, desethylamiodarone and mexiletine is advantageous in clinical practice. The presented LC-MS/MS method was validated for selectivity, matrix effect, linearity, accuracy, precision, carry-over and stability. The method was continuously evaluated during eight months of clinical use. The method was shown to be linear within the measured range of 0.1 to 10 mg/L for each component. The matrix effect was considered negligible. No interfering responses were found for amiodarone, desethylamiodarone and the isotopic-labeled internal standards. A constant and reproducible within-run contribution of 45.3 %, originating from the system, was identified for mexiletine. The systemic contribution to the peak area of the lowest quantifiable concentration of mexiletine affected the selectivity and carry-over effect measurements. Multiple measurements showed that regression adjusted concentrations were accurate and reproducible, indicating calibration correction was applicable. Sample stability was found to be within limits for all storage conditions and freeze–thaw cycles. Furthermore, long-term method evaluation with external controls resulted in stable measurements with a percentage coefficient of variance between 1.3 % and 6.3 %. The presented practical and reliable method is applicable for clinical TDM and will allow clinical practitioners to guide drug therapy of amiodarone and mexiletine.

Implications of Incorporating Plasma Lipoprotein Binding into a Physiologically-Based Pharmacokinetic Model: A Simulation Study with Amiodarone.

Although various lipophilic drugs are bound to lipoproteins, lipoprotein binding in plasma is not usually considered in current physiologically-based pharmacokinetic (PBPK) models. Amiodarone is extensively bound to serum triglyceride-rich lipoproteins. Total plasma amiodarone concentration, which is the sum of both unbound and bound concentrations, increases with increasing serum triglyceride levels. We investigated the impact of lipoprotein binding on amiodarone pharmacokinetics using PBPK modeling and simulations. An amiodarone PBPK model that incorporates plasma lipoprotein binding (LPP model) was developed based on the correlation between serum triglyceride levels and lipoprotein-bound amiodarone. The predicted unbound fraction of amiodarone in plasma and systemic clearance in the LPP and base models (with albumin binding only) were similar, but the coefficients of variation for the LPP model were greater than those for the base model and were closer to the observed data. The total plasma amiodarone concentration predicted using the LPP model increased with higher levels of plasma lipoprotein binding and serum albumin. In contrast, changes in plasma lipoprotein binding and serum albumin levels did not influence the predicted unbound plasma amiodarone concentration at steady-state. This study demonstrates that incorporating plasma lipoprotein binding into a PBPK model improves the accuracy of predicting interindividual variabilities in amiodarone clearance by more reliably predicting the interindividual variability in the plasma unbound fraction of amiodarone. Plasma lipoprotein binding should be considered in PBPK modeling and simulations for lipoprotein-associated drugs if there is available information on the relationship between plasma lipoprotein binding and hyperlipidemia.

In Vivo Evaluation of the Pharmacokinetic Interaction between Levothyroxine and Amiodarone in Rat Plasma: Evaluation of Importance of Therapeutic Drug Monitoring during Co-Therapy.

Amiodarone-induced thyrotoxicosis (AIT) is a common condition in patients who are receiving amiodarone for cardiac arrhythmia. This risk is elevated in iodine-deficient regions. Levothyroxine is the standard treatment for patients with hypothyroidism. This investigation is concerned with the evaluation of the possible pharmacokinetic interaction between amiodarone and levothyroxine upon co-therapy in rats and to investigate the cause of thyrotoxicosis. A selective, sensitive and precise RP-HPLC method was developed for the simultaneous determination of levothyroxine and amiodarone in rat plasma. A stationary phase of C18 Xterra RP column and a mobile phase consisting of acetonitrile: acidified water with 0.1% trifluoracetic acid (pH = 4.8) with gradient elution were used. The experiment was conducted at ambient temperature with flow rate of 1.5mL/min for the chromatographic separation and quantitation of the investigated drugs. Protein precipitation with methanol was applied for the analysis of the two drugs in rat plasma. The method was linear over concentration range of 5-200μg/mL for both levothyroxine and amiodarone. The European Medicines Agency guideline was applied for the validation of the developed bioanalytical method. The method was successfully applied to in vivo pharmacokinetic study in which levothyroxine and amiodarone were quantified in plasma of rats after receiving an oral dose of levothyroxine and amiodarone. After the calculation of the pharmacokinetic parameters, a statistical analysis was performed to elucidate the existence of significant difference between test and control groups in rats. The combination of levothyroxine and amiodarone significantly decreased levothyroxine bioavailability in rats, making the therapeutic drug monitoring mandatory in patients receiving levothyroxine and amiodarone. In addition, the increased clearance of levothyroxine upon the co-administration with amiodarone may explain the reported hypothyroidism.

Importance of in vitro conditions for modeling the in vivo dose in humans by in vitro-in vivo extrapolation (IVIVE).

In vitro studies are increasingly proposed to replace in vivo toxicity testing of substances. We set out to apply physiologically based pharmacokinetic (PBPK) modeling to predict the in vivo dose of amiodarone that leads to the same concentration-time profile in the supernatant and the cell lysate of cultured primary human hepatic cells (PHH). A PBPK human model was constructed based on the structure and tissue distribution of amiodarone in a rat model and using physiological human parameters. The predicted concentration-time profile in plasma was in agreement with human experimental data with the unbound fraction of amiodarone in plasma crucially affecting the goodness-of-fit. Using the validated kinetic model, we subsequently described the in vitro concentration-time data of amiodarone in PHH culture. However, this could be only appropriately modeled under conditions of zero protein binding and the very low clearance of the in vitro system in PHH culture. However, these represent unphysiological conditions and, thus, the main difference between the in vivo and the in vitro systems. Our results reveal that, for meaningful quantitative extrapolation from in vitro to in vivo conditions in PBPK studies, it is essential to avoid non-intended differences between these conditions. Specifically, clearance and protein binding, as demonstrated in our analysis of amiodarone modeling, are important parameters to consider.

LC-MS Method for Determining Amiodarone and Desethylaminodarone in Rat Plasma Used in Endogenous Overdosing Conditions Following Lipolysis

Abstract Objective: The purpose of this study was to develop a LC-MS method to determine amiodarone (AMI) and its major metabolite desethylamiodarone (DEA) from rat plasma released from the adipose tissue of AMI treated rats subjected to a weight gain/weight loss cycle. Methods: Separation of the compounds was performed on a Kinetex 2.6 μm C18 100 x 4.6 mm column under isocratic conditions using a mixture of acetonitrile: 0.1% formic acid 65:35 at a flow rate of 0.5 ml/min. Detection of the analyte was performed by electrospray positive ionization, the monitored ions being 135 m/z from 646 for AMI and 135 m/z of 618 for DEA. Analytes were extracted after plasma protein precipitation with methanol. Results: The developed method presented specificity and linearity on the concentration range of 25-2500 ng/ml plasma for AMI and 2.5-1250 ng/ml plasma for DEA and the precision and accuracy of the method at all of quality control concentration levels including LLOQ were according to official guidelines for validating analytical methods. Conclusions: A sensitive and accurate LC-MS method has been developed with a much lower LLOQ than literature data to detect the plasma concentration differences of the studied analytes that result from forced lipolysis and mobilization from the adipose tissue.

First liquid chromatographic method for the simultaneous determination of amiodarone and desethylamiodarone in human plasma using microextraction by packed sorbent (MEPS) as sample preparation procedure

For the first time a simple and fast high-performance liquid chromatography (HPLC) method using a novel sample preparation procedure based on microextraction by packed sorbent (MEPS) was developed and validated for the determination of amiodarone (AM) and its main metabolite desethylamiodarone (DEA) in human plasma. Chromatographic separation of the analytes (AM and DEA) and tamoxifen, used as internal standard (IS), was achieved within less than 5min on a LiChroCART Purospher® Star C18 column (55mm×4mm, 3μm). The mobile phase consisting of 50mM phosphate buffer with 0.1% formic acid (pH 3.1)/methanol/acetonitrile (45:5:50, v/v/v) was pumped isocratically at a flow rate of 1.2mL/min. The detection was carried out at 254nm. Calibration curves were linear (r2≥0.9976) in the ranges of 0.1–10μg/mL for AM and DEA. The limits of quantification were established at 0.1μg/mL for AM and DEA. The overall imprecision did not exceed 6.67% and inaccuracy was within ±9.84%. The overall mean recovery of AM and DEA ranged from 58.6% to 68.2%. Neither endogenous nor tested exogenous compounds were found to interfere at retention times of the analytes (AM and DEA) and IS. This new MEPS/HPLC method was also applied to real samples obtained from polymedicated patients receiving AM therapy. Thus, this bioanalytical method seems to be a useful tool for therapeutic drug monitoring of patients under AM treatment and also to support other clinical pharmacokinetic-based studies involving this drug, such as bioavailability/bioequivalence studies.

Amiodarone and desethylamiodarone tissue uptake in rats chronically treated with amiodarone is non-linear with the dose

Four groups of rats were given amiodarone chronically at 25, 37.5, 50, 75 mg kg-1/12 h for 3 weeks; on day 21 the animals were killed and blood, plasma, heart, lung, liver and fat were collected and assayed for amiodarone and desethylamiodarone. Amiodarone plasma concentrations ranged from 0.74 to 4.68 micrograms mL-1 and desethylamiodarone from 0.08 to 2.05 micrograms mL-1. Plasma, blood and tissue concentrations of amiodarone and desethylamiodarone increased significantly with the dose. Blood/plasma and tissue/plasma partition ratios of amiodarone and desethylamiodarone increased significantly at the higher doses. Blood/plasma ratio was a good predictor of tissue/plasma ratios of amiodarone and its metabolite, except in fat. Total phospholipid concentrations in lung were correlated with amiodarone and desethylamiodarone concentrations in plasma, blood and lung.

Intravenous Lipid Emulsion Sequesters Amiodarone in Plasma and Eliminates Its Hypotensive Action in Pigs

Our objective is to investigate to what extent amiodarone is sequestered by intravenously administered lipid emulsion in plasma of pigs and whether the lipid emulsion inhibits amiodarone-induced hypotension. Twenty anesthetized pigs received randomly 1.5 mL/kg bolus injection of olive/soybean oil-based 20% lipid emulsion (lipid group, n=10) or Ringer's acetate solution (control group, n=10) in 1 minute, followed by a continuous infusion of either solution for 30 minutes at 0.25 mL/kg per minute. Simultaneously with these continuous infusions, amiodarone hydrochloride was infused for 20 minutes at 1 mg/kg per minute in both groups. Plasma amiodarone concentration and mean arterial blood pressure were evaluated at predetermined intervals. Plasma amiodarone concentration in the lipid group increased more steeply during the amiodarone infusion than in the control group, at 20 minutes being a median 96.8 mg/L (interquartile range [IQR] 85.4, 102.0 mg/L) in the lipid group and median 21.5 mg/L (IQR 18.9, 22.3 mg/L) in the control group (difference 75.3 mg/L; 95% confidence interval [CI] 65.3 to 85.3 mg/L). After the separation of lipids from plasma by differential centrifugation, less amiodarone was contained in the lipid-poor aqueous fraction. At 20 minutes, the median was 13.3 mg/L (IQR 12.0, 13.7 mg/L), and the difference compared with the total plasma amiodarone concentration was -83.6 mg/L (95% CI -93.3 to -73.8 mg/L). In the lipid group, mean arterial blood pressure was not altered during the continuous amiodarone infusion. In the control group, mean arterial blood pressure decreased from baseline at 11 minutes, and the median was 52 mm Hg (IQR 51, 80 mm Hg) and the difference from baseline was 26 mm Hg (95% CI 9 to 43 mm Hg). Mean arterial blood pressure at 21 minutes also remained below the baseline, and the median was 57 mm Hg (IQR 50, 68 mm Hg) and the difference from baseline was 21 mm Hg (95% CI 9 to 33 mm Hg). Amiodarone was sequestered to a great extent by the intravenously administered lipids in plasma, which completely prevented the decrease in arterial blood pressure caused by amiodarone infusion. Further studies are needed to evaluate the clinical usefulness of intravenous lipid emulsion as an antidote in amiodarone overdoses.

Simultaneous measurement of amiodarone and desethylamiodarone in human plasma and serum by stable isotope dilution liquid chromatography–tandem mass spectrometry assay

A stable isotope dilution liquid chromatography–electrospray ionization tandem mass spectrometry (LC–MS/MS) assay to measure amiodarone, the most frequently used agent for maintaining sinus rhythm in patients with atrial fibrillation, and its major metabolite desethylamiodarone in human plasma and serum was developed. Measurement of amiodarone and desethylamiodarone was performed during a 4.0-min run-time using amiodarone-D 4 and desethylamiodarone-D 4 as internal standards. Calibration curves covering 12 calibrators measured in four replicates each for the analysis of both amiodarone and desethylamiodarone were linear and reproducible in the range of 0.01–40.0 mg/L ( r > 0.999). Limits of detection in plasma matrix were 2.7 μg/L for amiodarone and 1.9 μg/L for desethylamiodarone, and lower limits of quantification in plasma matrix were 7.5 μg/L for amiodarone and 2.5 μg/L for desethylamiodarone. Interassay imprecision and inaccuracy were <8% and <9% for both substances. Mean extraction yield was 99.6% (range 92.6–107.7%) for amiodarone and 90.2% (range 80.0–94.7%) for desethylamiodarone. Agreement was moderate for amiodarone ( n = 162) and desethylamiodarone ( n = 117), respectively, between the present method and a HPLC method with UV detection using a commercially available reagent set for the HPLC analysis of these drugs. The Passing–Bablok regression line was HPLC = 0.98 (LC–MS/MS) + 0.10 [mg/L]; r = 0.94 for amiodarone and HPLC = 1.05 (LC–MS/MS) + 0.02 [mg/L]; r = 0.90 for desethylamiodarone. This sensitive and interference-free LC–MS/MS assay permits rapid and accurate determination of amiodarone and desethylamiodarone in human plasma and other body fluids.

Determination of the class III antiarrhythmic drugs dronedarone and amiodarone, and their principal metabolites in plasma and myocardium by high-performance liquid chromatography and UV-detection

Dronedarone, a noniodinated benzofuran derivative of amiodarone, is believed to have a better side effect profile, and is currently undergoing phase III clinical trials. A novel method was developed for the determination of dronedarone and its principal metabolite debutyldronedarone in both plasma and myocardial tissue by high-performance liquid chromatography (HPLC) coupled with UV-detection. The assay was also validated for determination of amiodarone and desethylamiodarone. Samples were obtained from healthy humans (plasma) and goats (plasma and myocardium). Sample preparation included deproteinization with acetonitrile and extraction with a mixture of heptane and dichloromethane (50/50, v/v). Chromatographic separation was performed on a Pathfinder PS polymeric C18 column (50 mm × 4.6 mm, 2.5 μm) with a mobile phase of acetonitrile, isopropanol, water and ammonia (80/10/10/0.025, v/v/v/v) at a flow-rate of 1 ml/min. Calibration curves of all analytes were linear in the range of 0.01–5 μg/ml for plasma samples, with a lower limit of quantification (LLOQ) of 0.04 μg/ml. For myocardial tissue samples, linear curves of all analytes were observed in the range of 0.02–500 μg/g, with a LLOQ of 0.08 μg/g. Within- and between-day precision was <18%, and within- and between-day accuracy ranged from 97.5 to 109.7%, with a recovery of 67.6–79.9%. The present method enables sensitive and specific detection of dronedarone, amiodarone and principal metabolites in plasma as well as myocardial tissue.

Histopathological and Biochemical Toxic Effect of Amiodarone on Thyroid Gland in Albino Rat

Backgrounds: Amiodarone AMD (Cordarone) was a benzofuran derivative, used in management of angina and refractory ventricular arrhythmia. Its effect on the thyroid gland structure and function was investigated in this study. Material and Methods: Fifty adult male albino rats were used and divided into three groups. The first group was consisted of 10 rats which served as control, received distilled water orally (1ml). The second group was consisted of 20 rats used as therapeutic dose treated group, received 40 mg/Kg b. w. of amiodarone while the third group was consisted of 20 rats used as a toxic dose treated group which received 60 mg/Kg b. w. of amiodarone orally daily for three months. Body weight of animals was determined. Serum concentration of tri-iodothyonine (T3), thyroxine (T4), thyrotrophin (TSH), interleukin 6 (IL6), tumour marker P53 and tissue residue for amiodarone in plasma, fat, liver, lung, thyroid gland and heart was determined. Results: Specimens from thyroid gland were taken and prepared for light and electron microscope examination. Highly significant decrease in body weight (P<0.001) were observed in both therapeutic and toxic doses treated groups in comparison to the control one. A very highly significant increase (P<0.001) of serum (T4 & T3) with Concomitant suppression of (TSH) (P<0.001). Serum levels of IL6 and P53 showed also a very highly significant increase (P<0.001). Amiodarone concentration in plasma, fat, liver, lung, thyroid gland and heart showed significant increase in therapeutic dose treated group and highly significant increase in toxic dose treated group. Histopathological examination of thyroid gland of therapeutic dose treated group by light microscope showed marked evidence of thyotoxicosis in the form of microcystic follicular changes and peripheral scalloping, cellular degeneration with scanty cytoplasm and vesicular nuclei appeared. These changes became more severe in toxic dose treated group in the form of epithelial hyperplasia with atypical nuclear features. Thyroid tissue damage with haemorrhage and necrosis. Electron microscopic examination showed a remarkable cellular changes in the form of dilated rouph endoplasmic reticulum, inclusion lysosomes, dilated Golgi bodies, mitochondrial distension and nuclear degeneration. In both treated groups these changes were dose related.

The Influence of Hyperlipoproteinemia on in Vitro Distribution of Amiodarone and Desethylamiodarone in Human and Rat Plasma

To study the effect of hyperlipoproteinemia on in vitro distribution of amiodarone (AM) and its prevalent metabolite desethylamiodarone (DEA) in human and rat plasma. Human and rat normolipidemic (NL) and hyperlipidemic (HL) plasma were spiked with AM and DEA. The fractions (high and low density lipoproteins, triglyceride rich lipoproteins and lipoprotein deficient plasma) were separated using ultracentrifugation. Human and rat displayed similar patterns in terms of association of AM and DEA in NL plasma, in which the highest and lowest associations were observed in lipoprotein deficient (LPDP) and triglyceride (TRL) rich plasma fractions, respectively. In HL a substantial shift was observed in partitioning of AM and DEA mostly to TRL. The shift of AM and DEA into TRL fraction of HL plasma was more drastic for rat than human. In HL, association of AM with rat LPDP and HDL fractions were 10 and 26-fold lower than in the corresponding human fractions, respectively. The DEA:AM ratio in rat, but not human, was significantly affected by HL. HL caused a major shift of AM and DEA to TRL fraction in both species. The findings were consistent with the higher AM concentrations previously noted in HL rats given the drug.

Determination of amiodarone and desethylamiodarone in horse plasma and urine by high-performance liquid chromatography combined with UV detection and electrospray ionization mass spectrometry

A rapid method for the quantification of amiodarone and desethylamiodarone in animal plasma using high-performance liquid chromatography combined with UV detection (HPLC-UV) is presented. The sample preparation includes a simple deproteinisation step with acetonitrile. In addition, a sensitive method for the quantification of amiodarone and desethylamiodarone in horse plasma and urine using high-performance liquid chromatography combined with electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) is described. The sample preparation includes a solid-phase extraction (SPE) with a SCX column. Tamoxifen is used as an internal standard for both chromatographic methods. Chromatographic separation is achieved on an ODS Hypersil column using isocratic elution with 0.01% diethylamine and acetonitrile as mobile phase for the HPLC-UV method and with 0.1% formic acid and acetonitrile as mobile phase for the LC-MS/MS method. For the HPLC-UV method, good linearity was observed in the range 0-5 microg ml(-1), and in the range 0-1 microg ml(-1) for the LC-MS/MS method. The limit of quantification (LOQ) was set at 50 and 5 ng ml(-1) for the HPLC-UV method and the LC-MS/MS method, respectively. For the UV method, the limit of detection (LOD) was 15 and 10 ng ml(-1) for amiodarone and desethylamiodarone, respectively. The LODs of the LC-MS/MS method in plasma were much lower, i.e. 0.10 and 0.04 ng ml(-1) for amiodarone and desethylamiodarone, respectively. The LODs obtained for the urine samples were 0.16 and 0.09 ng ml(-1) for amiodarone and desethylamiodarone, respectively. The methods were shown to be of use in horses. The rapid HPLC-UV method was used for therapeutic drug monitoring after amiodarone treatment, while the LC-MS/MS method showed its applicability for single dose pharmacokinetic studies.

Simultaneous estimation of amiodarone and desethylamiodarone in human plasma by high-performance liquid chromatographic method

A high performance liquid chromatographic method is described for simultaneous estimation of amiodarone and its metabolite desethylamiodarone in plasma. After precipitation with acetonitrile, the separation of amiodarone, desethylamiodarone and internal standard was accomplished using reversed phase chromatography. The mobile phase, a combination of ammonium acetate (pH 3.5 adjusted with ortho phosphoric acid) and acetonitrile was run isocratically through a C18 analytical column. The UV detection was done at 242 and 247 nm for amiodarone and desethylamiodarone respectively. Analytical run time was 10 min. Mean recovery was 84% for 0.5 µg/ml concentrations. The assay exhibited good linear relationship between peak height ratios and plasma concentration. Quantification limit was at least 0.01 µg/ml of amiodarone and desethylamiodarone. Accuracy and precision were over the concentration range of 0.01-10 µg/ml. Assay was successfully applied to the measurement of amiodarone and its metabolite desethylamiodarone in human plasma of patients who were on long-term oral therapy on amiodarone.

Identification and quantitation of novel metabolites of amiodarone in plasma of treated patients

In mammals, mono- N-desethylamiodarone (MDEA) is the only known metabolite of amiodarone. Our previous experiments demonstrated that in vitro MDEA may be hydroxylated, N-dealkylated, and deaminated. In this report, we investigated the concentration of these microsomal metabolites in the plasma of patients receiving amiodarone. The presence of the hydroxy-amiodarone and deiodinated amiodarone was also additionally investigated. A high-performance liquid chromatography–atmospheric pressure chemical ionization tandem mass spectrometry (HPLC–APCI-MS/MS) quantitative assay using morpholine–amiodarone as internal standard was developed for measuring these metabolites in the range of 3–250 ng ml −1. In the concentration ranges 5–50 and 50–250 ng ml −1, the coefficients of variation of the measurements were less than 14 and 7%, respectively. The concentrations of investigated compounds in plasma of patients ( n = 14) receiving amiodarone (0.2 g day −1, orally for >2 months) varied inter-individually and were 140.0 ± 85.2, 39.1 ± 20.8, and 26.2 ± 15.2 ng ml −1 for 3′OH-mono- N-desethylamiodarone, di- N-desethylamiodarone, and deaminated amiodarone, respectively. The concentrations of MDEA and amiodarone in these samples were 970 ± 347 and 11163 ± 435 ng ml −1, respectively. In contrast, the studied compounds were not detectable in plasma samples from eight patients receiving amiodarone intravenously. Qualitatively, in the plasma of patients receiving amiodarone orally, hydroxylated amiodarone was also positively detected by assaying the [ M + H] + ions at m/z 662, but the deiodo-metabolites of amiodarone were not detected using mass spectrometry. Thus, in humans, amiodarone and MDEA were biotransformed by dealkylation, hydroxylation, and deamination.

Pharmacokinetics and pharmacodynamic effects of amiodarone in plasma of ponies after single intravenous administration

Atrial fibrillation is a well-known heart disease in horses. The common therapy consists of administration of quinidine. More potent antiarrhythmic drugs have become available for human therapy and the use of these as alternatives to quinidine for equine antiarrhythmic therapy is a matter of interest. Amiodarone (AMD) is used in human medicine for treatment of many arrhythmias, including atrial fibrillation. Its disposition in horses has not yet been investigated. The purpose of this study was to measure the effect of single intravenous doses of amiodarone (5 and 7 mg/kg) on the surface electrocardiogram (ECG) of healthy minishetland ponies during the first 2 days after drug administration and to calculate pharmacokinetic parameters with a physiologically based pharmacokinetic model (PBPK) using amiodarone and desethylamiodarone (DAMD) plasma levels that were determined by high-performance liquid chromatography (HPLC). As expected for a K +-channel-blocker, the main effect on the measured ECG could be seen on the ventricular complex, as the QT interval and the T wave showed statistically significant alterations. The doses investigated were well tolerated clinically. Results from the pharmacokinetic model were found to compare well with literature data of rats, dogs, and humans. It showed a rapid distribution in the tissue, beginning with the rapidly perfused tissue, like the heart, followed by slowly perfused tissues, and finally an accumulation in fat. The half-life for total elimination was calculated to be 16.3 days with 99% eliminated by 97 days. The model predicts that approximately 96% of amiodarone is eliminated as desethylamiodarone in urine, 2% eliminated as desethylamiodarone in bile, and 2% as other metabolites.

Mechanism of the delayed onset of action after intravenous amiodarone for treatment of ventricular arrhythmias

AbstractThe onset of action of intravenous amiodarone (AM) for treatment of ventricular arrhythmias often occurs after at least several hours' delay. To investigate the mechanism of this delayed action, we gave i.v. AM at an initial loading dose of 2.5 mg/kg or 5.0 mg/kg over 10 min, followed immediately by infusion of 7.5 μg/kg.min or 10 μg/kg.min for 20 h in eight dogs. The concentration of AM and its major metabolite, N‐desethylamiodarone (DA), in plasma and myocardial tissue were determined immediately after the loading dose and at 20 h after infusion, respectively, while electrophysiologic parameters were measured at the same times. The concentration of AM and DA in plasma were also determined serially. The results showed that the concentration of AM or DA in plasma or myocardial tissue rose to the peak level within 5–15 min after the loading dose, the sinus cycle length and AV conduction Wenckebach point measured at this time increased significantly relative to baseline (P&lt;0.05), while the ventricular effective refractory period (VERP) and ventricular exciting time (VET) at this time did not increase significantly (P&gt;0.05). The concentration of AM or DA in plasma declined rapidly during the continuous infusion period and remained at a stable low level until infusion stopped. The concentration of AM or DA in the myocardial tissue at 20 h after continuous infusion was lower than immediately after the loading dose. The sinus cycle length and AV conduction Wenckebach point were shortened close to the baseline level, while the VERP and VET were unchanged 20 h after infusion. The delayed onset of action for treatment of ventricular arrhythmias after i.v. administration of AM cannot be explained by higher concentration of AM or its metabolite in myocardial tissue. The specific mechanism(s) of action of i.v. AM in its control of arrhythmias remain to be determined. Drug Dev. Res. 58:145–148, 2003. © 2003 Wiley‐Liss, Inc.

Determination of amiodarone and desethylamiodarone in human plasma by high-performance liquid chromatography–electrospray ionization tandem mass spectrometry with an ion trap detector

A sensitive and specific high-performance liquid chromatography–electrospray ionization-tandem mass spectrometry (HPLC–ESI-MS–MS) method has been developed for the simultaneous determination of amiodarone and desethylamiodarone in human plasma. After the addition of the internal standard tamoxifen, plasma samples were extracted using Oasis ® MCX solid-phase extraction cartridges. The compounds were separated on a 5 μm Symmetry C 18 (Waters) column (150×3.0 mm, internal diameter) with a mobile phase of acetonitrile–0.1% formic acid (46:54, v/v) at a flow-rate of 0.5 ml/min. The overall extraction efficiency was more than 89% for both compounds. The assay was sensitive down to 1 μg/l for amiodarone and down to 0.5 μg/l for desethylamiodarone. Within-run accuracies for quality-control samples were between 95 and 108% of the target concentration, with coefficients of variation <8%. The proposed method enables the unambiguous identification and quantitation of amiodarone and desethylamiodarone in both clinical and forensic specimens.

Disposition of amiodarone in rats after single and multiple intraperitoneal doses.

The pharmacokinetics of amiodarone was studied after single and multiple dosing in two groups of male Wistar and Albino rats. The first group (40 rats) received a single intraperitoneal (i.p.) dose of amiodarone (100 mg/kg) and 4 rats sacrificed 1, 2, 4, 6, 12, 18, 24, 36, 48 and 72 hours post dosing. The second group (42 rats) received amiodarone (50 mg/kg, i.p. daily) for 5 days a week for 5 weeks and 6 rats were sacrificed at 1, 2, 3, 4, 5, 6 and 8 weeks. Rats of both groups were sampled for blood, heart, lung and fat and the concentrations of amiodarone in these samples were determined using High Performance Liquid Chromatography (HPLC). The elimination of amiodarone from plasma after single dose followed a biphasic pattern with a terminal half-life of 54.7+/-8.2 hours. The concentrations of amiodarone in the tissues were halved within 26.8, 34.9 and 37.45 hours in the heart, lung and fat, respectively. The average concentrations of amiodarone in plasma, heart, lung and fat after single dose were 1.24 microg/ml, 1.73 microg/mg and 29.01 microg/mg, respectivelly. The concentrations of amiodarone after multiple dosing were halved within 8.4, 5.5, 6.4 and 9.8 days, for the plasma, heart, lung and fat, respectively. The average concentrations of amiodarone in plasma, heart, lung and fat during multiple doses were 0.97 microg/ml, 1.41 microg/mg, 7.63 microg/mg and 65.01 microg/mg respectively. In conclusion, after multiple dosing, the elimination half-life of amiodarone and its fat contents were 3.7 and 2.8 times greater than that after single dosing. The excessive amount of amiodarone observed in fat tissues after multiple dosing is probably the reason for the prolonged elimination half-life. Based on the elimination half-lives data, the time to steady state is about two weeks and the drug should be withheld for less than a month if a patient required discontinuation because of serious adverse effects.

Disposition of amiodarone in rats after single and multiple intra-peritoneal doses.

The pharmacokinetics of amiodarone was studied after single and multiple dosing in two groups of male Wistar and Albino rats. The first group (40 rats) received a single intraperitoneal (i.p.) dose of amiodarone (100 mg/kg) and 4 rats sacrificed 1, 2, 4, 6, 12, 18, 24, 36, 48 and 72 hours post dosing. The second group (42 rats) received amiodarone (50 mg/kg, i.p., daily) for 5 days a week for 5 weeks and 6 rats were sacrificed at 1, 2, 3, 4, 5, 6 and 8 weeks. Rats of both group were sampled for blood, heart, lung and fat and the concentrations of amiodarone in these samples were determined using. The elimination of amiodarone from plasma after single dose followed a biphasic pattern with a terminal half-life of 54.7 +/- 8.2 hours. The concentrations of amiodarone in the tissues were halved within 26.8, 34.9 and 37.45 hours in the heart, lung and fat, respectively. The average concentrations of amiodarone in plasma, heart, lung and fat after single dose were 1.24 micrograms/ml, 1.73 micrograms/mg, 7.61 micrograms/mg and 29.01 micrograms/mg, respectively. The concentration of amiodarone after multiple dosing were halved within 8.4, 5.5, 6.4 and 9.8 days, for the plasma, heart, lung and fat, respectively. The average concentrations of amiodarone in plasma, heart, lung and fat during multiple doses were 0.97 microgram/mg, 7.63 micrograms/mg and 65.01 micrograms/mg respectively. In conclusion, after multiple dosing, the elimination half-life of amiodarone and its fat contents were 3.7 and 2.8 times greater than that after single dosing. The excessive amount of amiodarone observed in fat tissues after multiple dosing is probably the reason for the prolonged elimination half-life. Based on the elimination half-lives data, the time to steady state is about two weeks and the drug should be withheld for less than a mont if a patient required discontinuation because of serious adverse effects.