MEASUREMENT OF TISSUE-BOUND AMIODARONE AND ITS METABOLITES BY COMPUTED-TOMOGRAPHY

Amiodarone is strongly tissue-bound and serum levels are a poor guide to therapeutic efficacy. The electrocardiographic measure of the QT in terval corrected for heart rate (QTc) is a better guide but is unhelpf ul in patients with bundle branch block or U-waves on the electrocardi ogram. Myocardial amiodarone levels are the most accurate guide but ar e not easy to obtain. There is, however, a relationship between myocar dial concentration and hepatic concentration of amiodarone and its met abolites. Since amiodarone contains iodine, and there is hepatic uptak e, the increased hepatic attenuation from single slice computed tomogr aphy was compared with serum levels and the electrocardiographic QTc i n 12 patients before and during amiodarone therapy. Hepatic attenuatio n increased by a mean value of 18.25 HU over a 12 month study period. This increase correlated well with increased QTc (r=0.83) and with ser um amiodarone levels (r=0.89), but less well with serum desethyl amiod arone levels (r=0.43). An iodine-containing phantom was used to constr uct a curve of attenuation against iodine concentration in mol/l. Thus an indirect measurement of amiodarone concentration in g/l wet weight of liver could be determined.