MEASUREMENT OF SERUM AMIODARONE AND DESETHYLAMIODARONE BY HPLC - ITS USEFULNESS IN THE FOLLOW-UP OF ARRHYTHMIC PATIENTS TREATED WITH AMIODARONE

Amiodarone is an antiarrhythmic agent used for the treatment of suprav entricular and ventricular arrhythmias. Owing to its narrow therapeuti cal range, monitoring of drug concentration is mandatory. The circulat ing and tissue levels of amiodarone and of ifs main endogenous metabol ite, N-desethyl-amiodarone, are currently measured by means of HPLC pr ocedures, which are tedious and time-consuming, and often beset with p roblems and drawbacks. We have developed a new chromatographic assay f or the simultaneous measurement of amiodarone and N-desethyl-amiodaron e in serum samples., and tested its usefulness in the follow-up of 14 patients (8 men and 6 women, age range 40-65 years) with complex ventr icular arrhythmias, treated with amiodarone for at least 5 weeks. This assay uses trifluoperazine dihydrochloride as internal standard and a preliminary extraction of serum samples with isopropyl ether. The ass ay procedure was the following. 350 mu l patient's serum, to which 1 m u g trifluoperazine was added, were extracted with 280 mu l isopropyl ether. After mixing and centrifugation, 50 mu l of the organic layer w ere filtered and then injected onto the HPLC system (15 cm x 3.9 mm Re solve 5-mu m spherical silica column), the elution rate was 1.8 ml/min (mobile phase, 990 ml of methanol and 80 ml of ammonium sulfate buffe r) in isocratic condition. The rime for a complete assay of each serum sample was less than 20 min, and its working range was 0.1-5.0 mu g/m l of amiodarone. An excellent recovery of the drug from subtherapeutic al values up to toxic amiodarone concentrations was obtained. The infr a-assay precision of amiodarone assay ranged from 5 to 11%, while the between-assay precision from 8 to 13%. Following the results of amioda rone assay, if was possible to adjust the dose of drug administered in all patients, without increasing the amiodarone concentration beyond the toxic threshold level. The plateau of the circulating levels of th e drug was generally reached in about 5-12 days, at the acceptable the rapeutical range, from 0.5 to 2 mu g/ml. In conclusion, this chromatog raphic method for the assay of serum amiodarone levels is sufficiently simple, rapid and reliable to be considered a useful tool in the foll ow-up of arrhythmic patients chronically treated with amiodarone.