Value of hepatic computerized tomographic scanning during amiodarone therapy.

Amiodarone therapy is difficult to monitor because of the poor correlation between plasma amiodarone levels and clinical efficacy or toxicity. Monitoring tissue levels may give a better measure of effectiveness, but tissue levels cannot be easily measured. The iodine-containing amiodarone and its major metabolite, desethylamiodarone (DA), are highly tissue-bound, and it has been shown that computerized tomographic (CT) scanning of the abdomen will detect drug deposition in the liver. Ten patients receiving chronic amiodarone therapy were studied by abdominal CT scanning. Liver CT density was increased in 6; 68 to 94 CT units (normal 50 to 65) and liver/spleen relative CT density increased in 5; 1.4 to 2.0 (normal 1.0 to 1.3). Estimates of liver drug levels (based on a calibration curve with inorganic iodide) gave values of up to 3 g of amiodarone and DA per kilogram weight of liver. Absolute and relative liver CT density correlated significantly with plasma levels of DA (r = 0.65, p less than 0.05), but not with amiodarone (r = 0.55, p less than 0.1). No significant correlation was found with QTc intervals. This indirect estimate of liver deposition of amiodarone and DA may prove useful in guiding antiarrhythmic therapy.