Clinical pharmacokinetics of amiodarone

Amiodarone: pharmacology and antiarrhythmic and adverse effects

Amiodarone is a benzofuran derivative that has been effective for the treatment of both supraventricular and ventricular tachyarrhythmias. It has a large volume of distribution, moderate bioavailability and a long half-life. Its pharmacokinetics are not well understood and its tissue distribution is not typical of a 2-compartment model. Due to ocular, dermatologic, gastrointestinal, neurologic, cardiovascular, thyroid and pulmonary toxicity, amiodarone should be reserved for use in patients with refractory and/or life-threatening arrhythmias.

Rapid liquid chromatographic assay for the determination of amiodarone and its N-deethyl metabolite in plasma, urine, and bile

A rapid high-performance liquid chromatographic assay was developed for the determination of amiodarone (1) and its N-deethyl metabolite (desethylamiodarone, 2) in plasma, urine, and bile. Analysis was performed on a C18 reversed-phase column and precolumn using a mobile phase consisting of methanol:water:58% ammonium hydroxide (94:4:2) delivered at a flow rate of 1.5 mL/min. The eluant was monitored at 244 nm. Under these conditions, 1, 2, and the internal standard eluted with retention times of 5.5, 4.6, and 6.8 min, respectively. Samples (100 microL) of plasma were prepared by precipitating the plasma proteins with acetonitrile containing the internal standard and injecting an aliquot of the supernatant directly onto the column. Samples (100 microL) of urine and bile were prepared for injection by acidifying the sample with concentrated HCl and then extracting the mixture with six volumes of 2,2-dimethoxyproprane. The recovery of 1 and 2 from plasma was virtually complete. The recovery from urine and bile was 80-90% for 1 and 60-65% for 2. The limit of sensitivity of both compounds in plasma was 100 ng/mL. For urine and bile, the detection limits were 1 and 5 micrograms/mL, respectively. Over the plasma concentration range of 0.1-10.0 micrograms/mL, the within-day CV ranged from 1 to 10% for 1 and from 1 to 8% for 2. The between-day CV ranged from 2 to 12% and from 1 to 17% for 1 and 2, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro amiodarone protein binding and its interaction with warfarin

The binding of amiodarone to human plasma protein and to bovine serum albumin was studied by three different methods, ultracentrifugation, equilibrium dialysis and fluorescence spectroscopy. The fraction of amiodarone bound to plasma protein amounted to 96.3%. The changes in the binding properties of 1-anilino-naphthalene-8-sulfonate for bovine serum albumin using warfarin and amiodarone as independent inhibitors were analyzed in terms of binding site specificity. The findings indicated that amiodarone and warfarin have two different binding sites on bovine serum albumin, so a noncompetitive inhibition mechanism was indicated. On the basis of our data we cannot exclude other mechanisms of interaction besides direct displacement of one drug by another; nevertheless, metabolite interference between amiodarone and coagulation cofactors may better explain the enhancement of warfarin's pharmacological action in association with amiodarone.

Suppression of arrhythmias within hours after a single oral dose of amiodarone and relation to plasma and myocardial concentrations

In 65 patients a single oral dose of amiodarone (30 mg/kg) produced an antiarrhythmic effect on supraventricular or ventricular arrhythmias within 3 to 8 hours and lasted for 17 to 19 hours. On the second day a 15-mg/kg dose reproduced this effect within 3 to 9 hours. Plasma concentration of amiodarone increased to a maximum (2.2 +/- 1.7 mg/liter) mean +/- standard deviation) at 6 +/- 3.5 hours and plasma levels of N-desethylamiodarone (NDA) rose to 0.2 +/- 0.08 mg/liter at 12 +/- 6.4 hours. Sixty-one other patients were given a single 30-mg/kg dose 7 hours to 4 days before open heart surgery. Biopsies of the right atrial and left ventricular walls were taken during surgery. Myocardial concentration of amiodarone was maximal in the atrium after 7 hours (13 +/- 8 mg/kg) and in the ventricle after 24 hours (17 +/- 11 mg/kg). NDA myocardial concentration increased progressively until 24 hours and then remained stable over 4 days (1.5 mg/kg). The amiodarone myocardial to plasma concentration ratio was similar in the atrium and in the ventricle and averaged 22 and 10 for amiodarone and NDA, respectively. A significant relation existed between amiodarone concentration and the effect on ventricular premature complexes (r = 0.74, p less than 0.001) and between amiodarone plasma concentration and the effect on the atrioventricular conduction (r = 0.58, p less than 0.001). The plasma concentration of amiodarone corresponding to a 60% decrease in arrhythmias averaged 1.5 to 2 mg/liter.(ABSTRACT TRUNCATED AT 250 WORDS)

Amiodarone kinetics after single i.v. bolus and multiple dosing in healthy volunteers

We studied three healthy volunteers after a single i.v. bolus of amiodarone, during 1 month of chronic oral dosing and after the discontinuation of the drug. Blood concentrations of amiodarone declined rapidly in a bi-exponential fashion after i.v. bolus. The terminal half-life ranged from 10 to 17 h; after discontinuation of chronic treatment the terminal half-lives were 8-21 days. The i.v. data, the trough levels during multiple dosing and the washout phase could be simultaneously fitted using a triexponential equation. The subjects were carefully monitored for cardiac and thyroid function. One subject had to stop taking amiodarone because of profound bradycardia. A reduction of serum TT3 and FT3 concentrations and an increase of serum rT3 and FT4 was found.