Serum and myocardial kinetics of amiodarone and its deethyl metabolite after intravenous administration in rabbits.

The serum kinetics of amiodarone and its major metabolite the deethyl analogue were studied in rabbits after intravenous administration. The elimination of the drug and the metabolite from serum occurred as a biexponential function. Both compounds exhibited a rapid distribution phase (6.5 and 4.4 min, respectively) and had elimination half-lives of 136 and 235 min, respectively. There was a rapid uptake of both drugs by the myocardium, with maximal concentrations at 5 and 15 min. The myocardial concentrations were higher than the respective serum concentrations and declined with time. There was a wide scatter in myocardium-serum ratios, which ranged from 1 to 11 for amiodarone and 12 to 29 for the metabolite. Neither the drug nor the metabolite produced significant changes in the surface electrocardiogram after intravenous administration. These data suggest that accumulation of the metabolite does not account for the slow onset of action of amiodarone.