The pharmacological actions of amiodarone involve multiple molecular targets. Its primary target is the voltage-gated potassium channels in cardiomyocytes, including the rapid delayed rectifier potassium channel (hERG/IKr) and the slow delayed rectifier potassium channel (IKs), with an IC₅₀ of approximately 45 nM for inhibiting wild-type hERG potassium channels. Additionally, amiodarone potently inhibits sodium channels (INa), with an IC₅₀ of approximately 3.6 μM for binding to inactivated sodium channels; inhibits L-type calcium channels (ICaL); inhibits ATP-sensitive potassium channels (IC₅₀ of 19.1 μM); acts as a noncompetitive antagonist at α- and β-adrenergic receptors; and modulates thyroid function by inhibiting the peripheral conversion of T4 to T3, with its metabolite also blocking T3 binding to nuclear receptors.

Amiodarone exhibits multiple pharmacological activities in in vitro assays. At the ion channel level, amiodarone inhibits hERG potassium channel tail currents in a concentration-dependent manner, with an IC₅₀ of 117.8 nM for inward tail currents in 94 mM high potassium external solution. In guinea pig papillary muscle preparations, amiodarone at 44-88 μM inhibits Vmax without affecting resting membrane potential, demonstrating frequency-dependent Class I antiarrhythmic characteristics. In human ventricular myocardium and Purkinje fibers, amiodarone at 50-88 μM also suppresses depolarization-induced abnormal automaticity. At the cellular level, amiodarone at 1-6 μg/mL induces human embryonic lung fibroblast proliferation and myofibroblast differentiation via the ERK1/2 and p38 MAPK signaling pathways, while concentrations above 15 μg/mL induce apoptosis. In atrial tissue, amiodarone at 1×10⁻⁴ M decreases spontaneous heart rate by 13%, prolongs sinus node recovery time by 105%, prolongs the effective refractory period by 12%, and increases contractile force by 12%.

Amiodarone demonstrates clear antiarrhythmic effects in various animal models. In a canine coronary ligation/reperfusion-induced arrhythmia model, prior oral administration of amiodarone (40 mg/kg, 2 hours before operation) significantly suppressed the number of ectopic beats during ligation and the incidence of ventricular fibrillation during both ligation and reperfusion periods, at a dose that did not prolong the QT interval. In anesthetized dogs, intravenous amiodarone (3.0 mg/kg) exerted negative chronotropic, inotropic, and dromotropic effects, accompanied by transient hypotension followed by an increase in total peripheral vascular resistance, and significantly prolonged both the ventricular repolarization phase and the effective refractory period. In rabbit models, long-term intraperitoneal administration of amiodarone (50 mg/kg/day for 3-4 weeks) significantly reduced iK and ito current densities and inhibited the conversion of thyroxine (T4) to triiodothyronine (T3).

Receptor binding studies for amiodarone typically use radioligand binding assays. For cardiac muscarinic receptor binding experiments, the procedure is as follows: Canine cardiac sarcolemmal vesicles are isolated and purified, then incubated with [³H]quinuclidinyl benzilate (QNB, a muscarinic antagonist) in receptor-containing buffer to establish equilibrium binding systems. Competitive binding systems are also established, where various concentrations of amiodarone or carbachol (positive control) are added to the co-incubation mixture to determine the inhibitory constant and allosteric modulation properties of the drug on [³H]-QNB binding. For hERG potassium channel binding studies, whole-cell patch-clamp techniques are employed to record hERG potassium channel currents in HEK293 cells, with concentration-response curves used to determine the half-maximal inhibitory concentration (IC₅₀) of amiodarone, and site-directed mutagenesis combined with molecular docking are used to identify key amino acid residues involved in binding.

Cultured cardiomyocytes serve as an important model for studying the cellular mechanisms of amiodarone action. A typical protocol is as follows: Ventricular tissues are isolated from 1-3 day old SD or Wistar neonatal rats, and primary cardiomyocytes are obtained through enzymatic digestion and differential plating methods. The isolated cardiomyocytes are cultured in DMEM/F12 medium containing 10% fetal bovine serum in a 37°C, 5% CO₂ incubator. After stable cell adhesion, cells are treated with amiodarone at various concentrations (typically 0.01-100 μmol/L) for 3 hours, or with a fixed concentration (10 μmol/L) for different durations (0.5, 1, 3, 6 hours) to observe concentration-dependent and time-dependent effects of the drug on cellular functions. Experimental endpoints include whole-cell patch-clamp recording for ion current measurements, real-time quantitative PCR for detection of HCN channel gene expression levels, and assessment of parameters such as contractile activity and ATP content.

In vivo animal models often use dogs, rabbits, and rats to evaluate the antiarrhythmic activity of amiodarone. For the canine coronary ligation/reperfusion model, the experimental procedure is as follows: Female beagle dogs (8.5-12.5 kg) are selected and administered amiodarone (40 mg/kg orally) or an empty gelatin capsule (control group) 2 hours before surgery. After pentobarbital anesthesia and endotracheal intubation with artificial ventilation, the left chest is opened and the left anterior descending coronary artery is ligated for 30 minutes followed by reperfusion. Electrocardiogram is continuously recorded to monitor the number of ectopic beats, incidence of ventricular fibrillation, and changes in QT interval. Another commonly used protocol involves intravenous administration of amiodarone (3.0 mg/kg) in anesthetized dogs while monitoring heart rate, blood pressure, cardiac output, and electrophysiological parameters (e.g., effective refractory period). In rabbit experiments, amiodarone is typically administered intraperitoneally at doses of 20-50 mg/kg/day for 3-6 weeks, followed by electrophysiological assessments and tissue sample collection.

Absorption, Distribution and Excretion
The peak plasma concentration (Cmax) of amiodarone is typically reached 3 to 7 hours after administration. Following a single intravenous dose of amiodarone, the onset of action is generally 1 to 30 minutes, with therapeutic effects lasting 1 to 3 hours. The steady-state plasma concentration of amiodarone ranges from 0.4 to 11.99 μg/ml; for patients with arrhythmias, it is recommended to maintain a steady-state concentration between 1.0 and 2.5 μg/ml. It is noteworthy that the onset of action of amiodarone may sometimes begin after 2 to 3 days, but typically takes 1 to 3 weeks, even with a high loading dose. The bioavailability of amiodarone varies in clinical studies, averaging between 35% and 65%. Food Effects: In healthy subjects, a single 600 mg dose of amiodarone administered immediately after consuming a high-fat diet resulted in a 2.3-fold increase in AUC and a 3.8-fold increase in Cmax. Food also enhances absorption, reducing Tmax by approximately 37%. Amiodarone is primarily eliminated through hepatic metabolism and bile excretion. Small amounts of desethylamiodarone (DEA) can be detected in urine. In a pharmacokinetic study of 3 healthy individuals and 3 patients with supraventricular tachycardia (SVT), the volume of distribution (VOD) ranged from 9.26 to 17.17 L/kg in healthy volunteers and from 6.88 to 21.05 L/kg in SVT patients. Prescribing information indicates significant individual variability in the VOD of amiodarone, with an average VOD of approximately 60 L/kg. Amiodarone accumulates systemically, particularly in adipose tissue and highly vascularized organs, including the lungs, liver, and spleen. The major metabolite of amiodarone, desethylamiodarone (DEA), is present in higher concentrations in the same tissues as amiodarone. A clinical study showed that the clearance rate of amiodarone after intravenous administration was 220 to 440 ml/hr/kg in patients with ventricular fibrillation and ventricular tachycardia. Another study determined that the systemic clearance of amiodarone after a single intravenous injection ranged from 0.10 to 0.77 L/min. Renal impairment did not appear to affect amiodarone clearance, but hepatic impairment may have reduced it. Patients with cirrhosis showed significantly reduced peak DEA plasma concentrations (Cmax) and mean amiodarone concentrations, but no significant change in amiodarone plasma concentrations. Severe left ventricular dysfunction prolongs the half-life of DEA. Regarding monitoring: There are currently no guidelines for adjusting amiodarone dosage in patients with renal, hepatic, or cardiac abnormalities. Close clinical monitoring is recommended for patients receiving long-term amiodarone treatment, especially elderly patients and those with severe left ventricular dysfunction. Metabolism/Metabolites: This drug is metabolized by CYP3A4 and CYP2C8 enzymes to the major metabolite, desethylamiodarone (DEA). CYP3A4 enzymes are present in the liver and intestine. Hydroxyl metabolites of DEA have been identified in mammals, but their clinical significance remains unclear. Amiodarone's known metabolites include N-deethylamiodarone. Amiodarone is primarily metabolized in the liver via CYP2C8 (less than 1% of the unchanged drug is found in urine) and may affect the metabolism of several other drugs. The major metabolite of amiodarone is deethylamiodarone (DEA), which also has antiarrhythmic effects. Grapefruit juice inhibits amiodarone metabolism, leading to elevated serum amiodarone levels. Elimination pathway: Amiodarone is primarily eliminated via hepatic metabolism and bile excretion; very little amiodarone or DEA is excreted in urine. Half-life: 58 days (range 15-142 days). The terminal half-life of amiodarone varies from patient to patient, but is generally long, ranging from approximately 9-100 days. Half-life data vary depending on the source. According to amiodarone's prescribing information, the mean apparent plasma terminal elimination half-life of amiodarone is 58 days (range 15 to 142 days). The terminal half-life of the active metabolite (DEA) ranges from 14 to 75 days. One study showed that the plasma half-life of amiodarone after a single dose ranged from 3.2 to 79.7 hours.

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The pharmacokinetics of amiodarone are characterized by high lipophilicity and extreme inter-individual variability. Oral absorption is incomplete and variable, with bioavailability ranging from 22% to 86% and oral formulations showing approximately 37% bioavailability. Plasma protein binding is extremely high, at approximately 96%. Amiodarone has an extremely large volume of distribution and is widely distributed into highly lipophilic tissues including fat, muscle, liver, lungs, and skin. Its elimination half-life is extremely long, averaging 9-100 days, and can extend to 14-120 days or longer following chronic therapy. Amiodarone is metabolized by the hepatic CYP450 enzyme system, primarily catalyzed by CYP3A4 and CYP2C8, with the main active metabolite being desethylamiodarone. Excretion occurs mainly via feces (through bile), with only a small amount excreted in urine.

Toxicity Summary
The antiarrhythmic effect of amiodarone can be attributed to at least two main mechanisms. It prolongs the duration of the cardiomyocyte action potential (phase 3) and the refractory period, and acts as a non-competitive α and β adrenergic inhibitor. Toxicity Data
Intravenous injection, mice: LD50 = 178 mg/kg.

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Amiodarone has multi-organ toxicity and carries an FDA black box warning. Pulmonary toxicity is the most prominent, including hypersensitivity pneumonitis and interstitial/alveolar pneumonitis, with rates of clinically manifest disease as high as 17% in some patient series and a fatality rate of approximately 10%. Hepatotoxicity manifests as asymptomatic elevations of liver enzymes (occurring in 15%-50% of patients) and can progress to cirrhosis and even liver failure. Thyroid dysfunction is common (5%-10%) due to amiodarone's structural similarity to thyroxine, causing both hypothyroidism and hyperthyroidism. Cardiac toxicity includes exacerbation or induction of arrhythmias (approximately 2%-5% of patients), QT prolongation, and torsade de pointes. Ocular toxicity primarily presents as corneal microdeposits (occurring in the majority of treated patients, causing symptoms in approximately 10%, reversible) and rare optic neuropathy (which may lead to permanent blindness). Photosensitivity and blue-gray skin discoloration are also very common. Other toxicities include peripheral neuropathy and gastrointestinal reactions. Amiodarone can cross the placenta and cause fetal harm; its use during pregnancy should be avoided. Oral LD₅₀ in rats is >3000 mg/kg.

[1]. Singh, B.N. and E.M. Vaughan Williams, The effect of amiodarone, a new anti-anginal drug, on cardiac muscle. Br J Pharmacol, 1970. 39(4): p. 657-67.

[2]. Clinical efficacy of amiodarone as an antiarrhythmic agent. Am J Cardiol, 1976. 38(7): p. 934-44.

Pharmacodynamics
Intravenous amiodarone relaxes vascular smooth muscle, reduces peripheral vascular resistance (afterload), and slightly increases cardiac index. This route of administration can also reduce cardiac conduction, thereby preventing and treating arrhythmias. However, oral amiodarone does not cause significant changes in left ventricular ejection fraction. Similar to other antiarrhythmic drugs, controlled clinical trials have not demonstrated that oral amiodarone improves survival. Amiodarone prolongs QRS duration and QT interval. Furthermore, it reduces sinoatrial node automaticity and atrioventricular node conduction velocity. The automaticity of ectopic pacemakers is also suppressed. Because amiodarone contains a high concentration of iodine, it can interfere with normal thyroid function; therefore, taking amiodarone may also lead to thyrotoxicosis or hypothyroidism.

C25H29I2NO3

645.31

645.024

1951-25-3

Amiodarone-d10 hydrochloride;1261393-77-4;Amiodarone hydrochloride;19774-82-4;Amiodarone-d4 hydrochloride;1216715-80-8

2157

Colorless to light yellow oil

1.58 g/cm3

635.1ºC at 760 mmHg

156ºC

337.9ºC

4.95E-16mmHg at 25°C

6.936

0

4

11

31

547

0

CCCCC1=C(C(C2=CC(I)=C(OCCN(CC)CC)C(I)=C2)=O)C3=C(O1)C=CC=C3

IYIKLHRQXLHMJQ-UHFFFAOYSA-N

InChI=1S/C25H29I2NO3/c1-4-7-11-22-23(18-10-8-9-12-21(18)31-22)24(29)17-15-19(26)25(20(27)16-17)30-14-13-28(5-2)6-3/h8-10,12,15-16H,4-7,11,13-14H2,1-3H3

(2-butyl-1-benzofuran-3-yl)-[4-[2-(diethylamino)ethoxy]-3,5-diiodophenyl]methanone

Amiodaronum AratacCordarone Amiodarona Nexterone

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Note: Please store this product in a sealed and protected environment, avoid exposure to moisture.

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

DMSO: ≥ 175 mg/mL (~271.2 mM)

Solubility in Formulation 1: 2.5 mg/mL (3.87 mM) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), Suspended solution; with ultrasonication.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of DMSO stock solution (25.0 mg/mL) to 900 μL of 20% SBE-β-CD saline and mix well.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.5 mg/mL (3.87 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), Clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of DMSO stock solution (25.0 mg/mL) to 900 μL of corn oil and mix well.

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 (Please use freshly prepared in vivo formulations for optimal results.)