Metabolite Desethylamiodarone Research Articles

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.

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

To determine the clinical effects and pharmacokinetics of amiodarone after single doses of 5 mg/kg administered orally or intravenously. 6 healthy adult horses. 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. 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. 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.

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.

Tolvaptan Administration Does Not Affect Steady State Amiodarone Concentrations in Patients With Cardiac Arrhythmias

Tolvaptan, a nonpeptide selective vasopressin receptor (V2) antagonist, is in development for the treatment of congestive heart failure and hyponatremia. Tolvaptan is primarily metabolized via CYP3A4. This study was conducted to determine the extent of the pharmacokinetic interaction between tolvaptan and steady state amiodarone, an antiarrhythmic drug commonly prescribed for patients with congestive heart failure and a known inhibitor of other drugs metabolized by CYP3A4. This was a multicenter, open-label, 1-arm, 3-period, sequential treatment study conducted in 11 men (10) and women aged 49 to 80 years. They were primarily Caucasian (20) subjects, with a history of cardiac arrhythmias who were otherwise healthy. Subjects were to have been on oral amiodarone maintenance therapy of 200 mg/day for at least 10 months. All subjects took 200 mg amiodarone once daily on each study day; on days 3 and 4, they were also coadministered 30 and 90 mg of tolvaptan, respectively. The plasma concentrations of amiodarone and its metabolite desethylamiodarone were determined for 24 hours postdose on days 2, 3, and 4, tolvaptan concentrations were determined for 24 hours postdose on days 3 and 4. As determined by the ratio of the geometric means and 90% confidence intervals (0.5 to 2.0) for the maximal plasma concentration and the area under the curve during the dosing interval for both amiodarone and desethylamiodarone, tolvaptan coadministration had no effect on either amiodarone and desethylamiodarone disposition, as all the geometric mean ratios (amiodarone + tolvaptan [30 or 90 mg] vs amiodarone alone) were approximately 1. Tolvaptan coadministration does not alter steady-state amiodarone or desethylamiodarone concentrations. Tolvaptan concentrations did not appear to be different from historical controls. The most frequently reported adverse event was polyuria (15 of 21 subjects for amiodarone + 30 mg tolvaptan); an expected outcome due to the known potent aquaretic action of tolvaptan. The combination of amiodarone and tolvaptan was well tolerated.

Amiodarone induces apoptosis of human and rat alveolar epithelial cells in vitro.

The antiarrhythmic amiodarone (AM) and its metabolite desethylamiodarone (Des) are known to cause AM-induced pulmonary toxicity, but the mechanisms underlying this disorder remain unclear. We hypothesized that AM might cause AM-induced pulmonary toxicity in part through the induction of apoptosis or necrosis in alveolar epithelial cells (AECs). Two models of type II pneumocytes, the human AEC-derived A549 cell line and primary AECs isolated from adult Wistar rats, were incubated with AM or Des for 20 h. Apoptotic cells were determined by morphological assessment of nuclear fragmentation with propidium iodide on ethanol-fixed cells. Necrotic cells were quantitated by loss of dye exclusion. Both AM and Des caused dose-dependent necrosis starting at 2.5 and 0.1 microg/ml, respectively, in primary rat AECs and at 10 and 5 microg/ml in subconfluent A549 cells (P < 0.05 and P < 0.01, respectively). AM and Des also induced dose-dependent apoptosis beginning at 2.5 microg/ml in the primary AECs (P < 0.05 for both compounds) and at 10 and 5 microg/ml, respectively, in the A549 cell line (P < 0.01). The two compounds also caused significant net cell loss (up to 80% over 20 h of incubation) by either cell type at drug concentrations near or below the therapeutic serum concentration for AM. The cell loss was not due to detachment but was blocked by the broad-spectrum caspase inhibitor Z-Val-Ala-Asp-fluoromethylketone. Furthermore, the angiotensin-converting enzyme inhibitor captopril (500 ng/ml) and the angiotensin-receptor antagonist saralasin (50 microg/ml) significantly inhibited both the induction of apoptosis and net cell loss in response to AM. These results are consistent with recent work from this laboratory demonstrating potent inhibition of apoptosis in human AECs by captopril (Uhal BD, Gidea C, Bargout R, Bifero A, Ibarra-Sunga O, Papp M, Flynn K, and Filippatos G. Am J Physiol Lung Cell Mol Physiol 275: L1013-L1017, 1998). They also suggested that the accumulation of AM and/or its primary metabolite Des in lung tissue may induce cytotoxicity of AECs that might be inhibitable by angiotensin-converting enzyme inhibitors or other antagonists of the renin-angiotensin system.

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.

AMIODARONE-INDUCED PULMONARY TOXICITY IN FISCHER RATS: RELEASE OF TUMOR NECROSIS FACTOR ALPHA AND TRANSFORMING GROWTH FACTOR BETA BY PULMONARY ALVEOLAR MACROPHAGES

Amiodarone is an antiarrhythmic drug with numerous side effects, the most serious being the development of pulmonary toxicity. We have previously reported that a single intratra cheal instillation of amiodarone to Fischer 344 rats results in pulmonary fibrosis within 6 wk of treatment. Presently, the mechanism of amiodarone-induced pulmonary toxicity is unknown. Cytokines that stimulate fibroblast proliferation and/or collagen production may play a role in amiodarone-induced pulmonary toxicity. To investigate this possibility, female rats were given a single intratracheal instillation of amiodarone (6.25 mg/kg), its metabolite desethylamiodarone (5 mg/kg), or vehicle (sterile water). At I, 2, 3, or 6 wk after treatment the lungs were lavaged and the recovered cells were counted and identi fied. The alveolar macrophages were isolated by attachment to plastic petri dishes, cul tured overnight, and the spent media collected for tumor necrosis factor alpha (TNF-α) and transforming growth factor beta (TGF-β) analyses. Desethylamiodarone treatment resulted in a neutrophilic alveolitis, but the levels of TNF-α and TGF-β were not signifi cantly different from control animals. In contrast, amiodarone treatment resulted in a lym phocytic alveolitis and significantly higher amounts of TNF-α were observed at 3 and 6 wk after treatment. A trend toward higher levels of TCF-β was also noted in the amio-darone-treated group at wk 1-3 but the values were not significantly different from those of controls. In conclusion, the release of TNF-α may play a role in the development of amiodarone-induced pulmonary toxicity.

AMIODARONE-INDUCED PULMONARY TOXICITY IN FISCHER RATS: RELEASE OF TUMOR NECROSIS FACTOR ALPHA AND TRANSFORMING GROWTH FACTOR BETA BY PULMONARY ALVEOLAR MACROPHAGES

Abstract Amiodarone is an antiarrhythmic drug with numerous side effects, the most serious being the development of pulmonary toxicity. We have previously reported that a single intratra cheal instillation of amiodarone to Fischer 344 rats results in pulmonary fibrosis within 6 wk of treatment. Presently, the mechanism of amiodarone-induced pulmonary toxicity is unknown. Cytokines that stimulate fibroblast proliferation and/or collagen production may play a role in amiodarone-induced pulmonary toxicity. To investigate this possibility, female rats were given a single intratracheal instillation of amiodarone (6.25 mg/kg), its metabolite desethylamiodarone (5 mg/kg), or vehicle (sterile water). At I, 2, 3, or 6 wk after treatment the lungs were lavaged and the recovered cells were counted and identi fied. The alveolar macrophages were isolated by attachment to plastic petri dishes, cul tured overnight, and the spent media collected for tumor necrosis factor alpha (TNF-α) and transforming growth factor beta (TGF-β) analyses. Desethylamiodarone treatment resulted in a neutrophilic alveolitis, but the levels of TNF-α and TGF-β were not signifi cantly different from control animals. In contrast, amiodarone treatment resulted in a lym phocytic alveolitis and significantly higher amounts of TNF-α were observed at 3 and 6 wk after treatment. A trend toward higher levels of TCF-β was also noted in the amio-darone-treated group at wk 1-3 but the values were not significantly different from those of controls. In conclusion, the release of TNF-α may play a role in the development of amiodarone-induced pulmonary toxicity.

Antioxidant defence capacity modulation of two human cell lines by amiodarone and desethylamiodarone

Although the role of oxidative stress has recently been the subject of increased discussion in relation to the pathogenesis of amiodarone (AMIO) toxicity, the cellular mechanisms underlying the hepatic and pulmonary disorders remain unknown. In order to investigate the effects of AMIO and its active metabolite desethylamiodarone (DEA) on the cellular antioxidant status, defence capacities of liver and lung cell lines have been first compared with published data on normal corresponding cells. Glutathione content, superoxide dismutase (SOD) and glutathione-related enzymes were then determined in Hep 3B and L132 cells, after AMIO and DEA treatment. Although no glutathione peroxidase could be detected in either cell line, Hep 3B and L132 cells were able to express normal glutathione S-transferase (GSH-S-T) and glutathione reductase (GSSG-Rd) activities. The principal targets of AMIO and DEA were, respectively, GSH-S-T and GSSG-Rd in Hep 3B cells, while SOD was significantly decreased by both drugs in L132 cells. Concomitantly, glutathione status (defined as the ratio of oxidized to total glutathione) was altered in Hep 3B but not in L132 cells. These findings suggest that the first step of amiodarone-induced Hep 3B and L132 cell lesions may result from the overwhelming of their antioxidant defence system.

Role of Oxidative Stress in Amiodarone-induced Toxicity.

BACKGROUND: The clinical usefulness of amiodarone for the treatment of cardiac arrhythmias is limited by multiorgan toxicity, especially pulmonary and hepatic. There are conflicting reports in the literature regarding the role of free radicals in the initiation of amiodarone-induced toxicity. We evaluated the possible oxidative stress in a chronic model that is known to manifest pulmonary toxicity. METHODS AND RESULTS: A group of 20 Fischer-344 rats were injected with 60 mg/kg/day of amiodarone for 21 days. A control group of 20 animals received only saline injections. The alveolar macrophages obtained by lung lavage were incubated with hydroethidine and opsonized green fluorescent zymosan particles to measure oxidative and phagocytic activities by flow cytometry. Malondialdehyde levels were measured to assess the extent of lipid peroxidation in lung, liver, spleen, kidney, and heart. Total phospholipid levels in all the collected tissues and distribution of phospholipid classes in the lung and the liver were measured. The levels of amiodarone and its metabolite desethylamiodarone in serum and all collected tissues were measured by high-performance liquid chromatography. The phagocytic activity of th emacrophages from treated animals was decreased by 18-22% (P <.03) compared to controls; however, the oxidative activities of control and treated groups were not significantly different. The tissue malondialdehyde levels were not significantly different except in the spleen where they increased after amiodarone treatment (18.2 +/- 1.1 vs 23.7 +/- 2.8 µM/g tissue, P <.0001). Malondyaldehyde levels were not significantly different when normalized to lipid phosphorous content. Lung, liver, and spleen showed significantly higher phospholipid levels in the treated group. The tissue amiodarone and desethylamiodarone levels in the treated group were highest in spleen followed by lung, liver, kidney, and heart. CONCLUSIONS: The results show that amiodarone-induced pulmonary and hepatic toxicity is not directly mediated by oxidative stress; however, increased lipid peroxidation in the spleen, although secondary to phospholipidosis, may be physiologically significant.

High Performance Liquid Chromatographic Analysis of Some Antiarrhythmic Drugs in Human Serum Using Cyanopropyl Derivatized Silica Phase

Abstract A high performance liquid chromatographic determination of antiarrhythmic agents: propafenone (PPF) with its principal active metabolite 5-hydroxypropafenone (5-OHPPF), amiodarone (AD) with an active metabolite desethylamiodarone (DEAD), mexiletine (MEX) and diltiazem (DILT) in human serum is presented. The compounds are separated on Supelcosil LC-CN column at ambient temperature under isocratic conditions. For PPF, 5-OHPPF, MEX and DILT analysis the mobile phase: CH3CN: H2O: 0.5 M KH2PO4 (360:620:20 v/v) is pumped at a flow rate of 1.8 mL/min and the ultraviolet detection is performed at 210 nm. AD and DEAD are eluted with stronger mobile phase: CH3OH: CH3CN: H2O: 0.5 M KH2PO4 (480:136:360:24 v/v) at a flow rate of 1.5 mL/min and detected at 240 nm. Sample preparation is based on simple liquid-liquid extraction from acidified serum for AD and DEAD and on liquid-liquid extraction from alkalized serum followed by back extraction for PPF, 5-OHPPF, MEX and DILT analysis. Sensitivity of the assay was...

Disposition of intravenous amiodarone in subjects with normal and impaired renal function.

In a study designed to determine the influence of renal dysfunction on the disposition of amiodarone and its metabolite, desethylamiodarone (DEA), 30 subjects received a single 5 mg/kg intravenous dose of amiodarone over 15 minutes. Of the 30, 11 had normal renal function (group I; mean +/- SD glomerular filtration rate [GFR] = 118 +/- 20 mL/min/1.73 m2), 9 had renal impairment (group II; GFR = 23 +/- 10 mL/min/1.73 m2), and 10 were long-term hemodialysis patients (group III; 4 of these patients were studied during dialysis). Total and free concentrations of amiodarone and DEA were measured by high-performance liquid chromatography. There were no significant differences between the three groups in mean systemic clearance, steady state volume of distribution, or mean residence time of amiodarone. However, the area under the concentration-time curve (AUC) for amiodarone was significantly higher in group I than in group II, and this finding was related to total body weight. Free fraction was similar in groups I and III. The disposition of amiodarone and its metabolite DEA was similar in patients with normal renal function, moderate renal dysfunction, and end-stage renal disease. Thus, dosage adjustment in patients with renal impairment is not necessary based on this pharmacokinetic analysis.

Radiolabeling and biodistribution of amiodarone and desethylamiodarone

The antiarrhythmic drug amiodarone and its metabolite desethylamiodarone, were radiolabeled with sodium [ 123I]-iodide in >98% yield using the exchange labeling method. Biodistribution studies with 123I-amiodarone in mice showed high liver and lung uptake. Heart uptake of 0.98% of the injected dose (id) peaked at 5 min, with clearance seen over 60 min to 0.44% id. 123I-Desethylamiodarone ( 123I-DEA) showed heart uptake of 0.58% id peaking at 5 min, with slower clearance seen over 60 min to 0.43% id. These results indicate that both agents have poor selectivity as myocardial imaging tracers. Low 123I-DEA brain uptake at 5 min (0.49% id) and rapid washout after 60 min indicate that 123I-desethylamiodarone has limited application as a brain imaging agent.

Dihydropyridine-like effects of amiodarone and desethylamiodarone on thyrotropin secretion and intracellular calcium concentration in rat pituitary

Amiodarone (AM) and its major metabolite desethylamiodarone (DEA) are structurally similar to biologically active thyroid hormones. Amiodarone therapy is frequently associated with impairment of thyrotropic function, whose mechanisms are still controversial. Besides its effect on nuclear thyroid hormone binding. AM is able to displace dihydropyridine (DH) binding on membrane preparations from several tissues. By perifusing rat pituitary fragments and measuring thyrotropin (TSH) release we examined: the effect of AM on Ca(2+)-dependent and DHP-sensitive potentiation of the TSH response to thyrotropin-releasing hormone (TRH) induced by either triiodothyronine (T3, perifused for only 30 min before a TRH pulse) or by the prepro-TRH peptide 160-169 (PS4); and the effect of DEA on TRH-induced TSH response in the presence or absence of the DHP nifedipine. We show that AM reverses T3 or PS4 potentiation of the TSH response to TRH; this effect is specific because AM does not modify ionomycin potentiation of that response. In contrast, DEA significantly potentiates the TSH response to TRH and the DHP nifedipine reverses that potentiation. We also tested whether AM would change the acute T3-induced increase in intracellular Ca2+ concentration by measuring intracellular Ca2+ ([Ca2+])i with fura-2 imaging on primary cultures of pituitary cells. We show that AM reverses the effect of T3 on [Ca2+]i as well as the PS4-induced increase in [Ca2+]i. In contrast, DEA increases [Ca2+]i and nifedipine reverses this effect. Our results suggest that AM and DEA display DHP-like effects on TRH-induced TSH release, behaving either as a Ca2+ channel blocker (AM) or as a Ca2+ channel agonist (DEA).

Vitamin E reduces accumulation of amiodarone and desethylamiodarone and inhibits phospholipidosis in cultured human cells

Chronic administration of amiodarone (AMIO), widely used by clinicians for the treatment of therapy-resistant cardiac arrhythmias, is frequently associated with serious side-effects. AMIO and its main metabolite desethylamiodarone (DEA) are known to induce phospholipidosis in vivo and in cultured cells presumably by inhibition of lysosomal phospholipid degradation. D- α-Tocopherol = vitamin E ( α-TOC) was able to reduce AMIO and DEA toxicity in cell cultures. Results from the present study showed that α-TOC reduced phospholipidosis in cultured human skin fibroblasts chronically exposed to micromolar concentrations of AMIO and DEA and inhibited cumulative uptake of the drugs in a dose-dependent manner. A linear correlation was observed between cellular AMIO levels and phospholipid accumulation suggesting a stoichiometric relationship. α-TOC was also effective in clearing previously accumulated phospholipids after discontinuation of the drug treatment. The results can best be explained by an interference of α-TOC (a) with drug-phospholipid complex formation responsible for both phospholipid storage and drug accumulation, and (b) with pre-existing drug-phospholipid complexes, accelerating their dissociation and rendering phospholipids to substrates for lysosomal phospholipases. The finding raises hope that side-effects of AMIO and DEA can be prevented or made reversible by the administration of α-TOC. It must, however, be proven that the antiarrhythmic drug will still be effective.

β-Adrenergic receptors, voltage-operated Ca 2+-channels, nuclear triiodothyronine receptors and triiodothyronine concentration in pig myocardium after long-term low-dose amiodarone treatment

Similar features during chronic amiodarone treatment and hypothyroidism suggest that amiodarone induces a state of "triiodothyronine (T3)-resistance" or "cardiac hypothyroidism", which may predispose the heart to pump failure under conditions with severe strain, such as recovery after cardiac surgery. Disagreements exists as to how amiodarone, and possibly its main metabolite desethylamiodarone, act upon the various receptor systems in the heart. The aim of the present study was to elucidate whether chronic amiodarone treatment leads to a functional reduction in the number of myocardial nuclear T3 receptors, the myocardial tissue T3 concentration and the number of beta-receptors and voltage-operated Ca(2+)-channels. Finally, special attention was drawn to any changes that could contribute to explain previous reports on reduced haemodynamic reserve in animals exposed to severe cardiac strain, such as cardiac surgery. Pigs (72 +/- 2 kg) were assigned randomly to amiodarone treatment (20 mg.kg-1.day-1 for 30 +/- 1 days, N = 8); controls received no medical treatment (N = 6). The left ventricle was evaluated for beta-adrenergic receptors, voltage-operated Ca(2+)-channels, T3 nuclear receptors and tissue T3 concentration. Maximum binding capacity for beta-receptors and Ca(2+)-channels was reduced in amiodarone-treated pigs (by 38%, p < 0.05, and by 52%, p < 0.01) and correlated with tissue drug concentrations for both receptor types (p < 0.05). No changes were observed concerning nuclear T3 receptors. In vitro competition studies revealed that amiodarone, but not desethylamiodarone, possessed binding properties to Ca(2+)-channels, whereas neither of the compounds bound to beta-receptors. Desethylamiodarone, but not amiodarone, competitively inhibited T3 binding to its nuclear receptors. Myocardial T3 was undetectable (< 0.05 nmol/kg wet wt) in amiodarone-treated pigs. From our observations we suggest that the active metabolite desethylamiodarone, rather than the parent drug, is mainly responsible for the observed local hypothyroid-like effects during amiodarone treatment. The observed changes after treatment with low-dose amiodarone in pigs are likely to have biological implications. Functionally, the changes may imply reduced cardiac reserve during conditions of extraordinary strain.

Clinical measurement of serum amiodarone and desethylamiodarone by using solid-phase extraction followed by HPLC with a high-carbon reversed-phase column

We describe a rapid, simple HPLC method routinely used in our clinical laboratory for determining amiodarone and its metabolite desethylamiodarone. These compounds are released from serum proteins by pretreatment with an acidic solution and then extracted onto a C2 reversed-phase clean-up column. After elution from the extraction column, the compounds are separated and quantified by HPLC with a C18 reversed-phase column and spectrophotometric detection. The standard curves for the drug and metabolite are linear up to 20.0 mg/L, with a lower limit of detection of 0.16 mg/L. The CVs for intra-assay precision were 5.0% at 0.58 mg/L and 2.9% at 5.96 mg/L; for inter-assay precision, they were 9.6% at 0.52 mg/L and 6.1% at 2.09 mg/L. Lipemia, hemoglobin, and bilirubin up to 300 mg/L do not interfere with this assay. None of > 550 cardiac patients' samples tested contained a compound that interferes with this assay.

Cellular accumulation of amiodarone and desethylamiodarone in cultured human cells: Consequences of drug accumulation on cellular lipid metabolism and plasma membrane properties of chronically exposed cells

Amiodarone (AMIO), a potent antiarrhythmic drug, is clinically widely used despite its frequent side effects after chronic administration. These side effects coincide with an intralysosomal accumulation of AMIO and its main metabolite desethylamiodarone (DEA) and may be causally related to the drug-induced intracellular storage of phospholipids (PL). Kinetics of cellular uptake and release of radiolabelied AMIO and DEA were studied following single and multiple exposures of cultured human skin fibroblasts to 5 and 10 μM drug concentrations. AMIO and DEA were efficiently taken up into cultured cells. The rate of uptake was slower than that of other cationic amphiphilic drugs. The intracellular steady state concentrations were in the millimolar range suggesting a lysosomal trapping. Repetitive exposures of cultures resulted in a cumulative and partly saturable drug uptake. The accumulation of DEA was higher than that of AMIO throughout. AMIO and DEA previously taken up into the cells during a 2 hr exposure were completely released into the washing media, suggesting an exchangeable form of the accumulated drugs. Following repetitive exposures only part of the drugs was released. Under chasing conditions using washing media containing non-labelled AMIO and DEA respectively or ammonium chloride the release of the chronically accumulated 14C-labelled drugs was increased. This suggested a drug storage in the form of complexes in acidic compartments. Phospholipid (PL) content as well as individual PL fractions were changed in whole cells and in isolated plasma membranes. PL accumulation is assumed to occur by inhibition of PL degradation due to formation of non-degradable drug-PL complexes or by inhibition of phospholipase activities. Cellular PL accumulation seemed to interfere with PL recycling. Changes in PL composition of purified plasma membranes were in part complementary to the ones in whole cells. The alterations in membrane PL composition may explain the changes in membrane fluidity and the decrease in β-adrenoceptor density and in isoproterenol-stimulated cAMP formation. The results obtained provide an explanation for the pharmacokinetic, and possibly for the pharmacodynamic and also toxicological behaviour of AMIO and DEA in vivo.

The Utility of Serum Drug Level Monitoring During Therapy with Class III Antiarrhythmic Agents

Serum drug level monitoring facilitates dosage optimization of agents with a narrow therapeutic index. Concentration-dependent antiarrhythmic and toxic effects have been demonstrated for several class I drugs, whereas the concentration-effect relationships of class III antiarrhythmics are less well established. The efficacy and toxicity of amiodarone, in particular, may be determined more by extensive tissue deposition than by its serum concentration. Furthermore, accumulation of the active metabolite desethylamiodarone seems to play an additional role. The antiarrhythmic serum concentration range of sotalol is wide; monitoring is not required. The clinical utility of serum concentration measurements with the newly developed class III antiarrhythmic agents remains to be evaluated in properly planned therapeutic trials in patients with supraventricular and ventricular arrhythmias.

Use of amiodarone during pregnancy

Five cases are studied in which amiodarone (AM) was given during pregnancy, in two of them also during the breast feeding period, to estimate the risks for adverse effects. We measured the concentrations of AM and its major metabolite desethylamiodarone (DEA) in maternal plasma, cord plasma, infant plasma, placental tissue and breast milk and the thyroid hormones were measured in maternal and neonatal serum. Also, the neonates were examined for AM-associated adverse effects over a period varying from 8 months up to 5 years. We observed a limited maternal-fetal transfer of AM and DEA, while the concentration of DEA in placental tissue is relatively high. Considerable amounts of AM and DEA were present in breast milk. One infant appeared to be hypothyroid, detected by the neonatal thyroid screening. He was treated with triiodothyronine for weeks, until it was clear that the thyroid dysfunction was resolved. The other infants had normal screening results. No effect of the AM medication was observed on growth, liver function or cornea and skin. In conclusion: although pregnancy and lactation are no absolute contraindications for use of AM, special precautions are necessary. It is unavoidable that in some cases the pregnant mother, and especially her infant, becomes hypothyroid. AM has to be administered in the lowest possible dose, and the maternal and neonatal thyroid function must be controlled as long as the exposure to AM lasts.