Pulmonary sequestration of amiodarone and desethylamiodarone

We hypothesized that one of the reasons for the particular susceptibility of the lung toward the adverse effects from the antiarrhythmic agent amiodarone (A) could be a high pulmonary accumulation of this drug. This hypothesis was tested using the isolated perfused lungs of Fischer 344 and Sprague-Dawley rats and New Zealand White rabbits. Uptake of a 3 microM starting concentration of a mixture of A and [14C]A by the lung occurred rapidly in each species, and only 25.6, 19 and 16.4% of the initial concentration remained in the perfusate at the end (60 min) of the experiment in Fischer 344, Sprague-Dawley rats and rabbits, respectively. No metabolism of A was detected by the high-performance liquid chromatography technique. Raising the initial concentration of A from 0.3 to 120 microM (n = 26) in the Fischer 344 rats apparently did not saturate the uptake process, and the tissue/medium ratio averaged 122.5. The uptake of desethylamiodarone (DEA), the main metabolite of A in vivo, was more extensive (tissue/medium ratio = 506) than that of the parent compound. DEA also was not metabolized by the isolated perfused lungs. Lung homogenate incubations fortified with cofactors did not metabolize A or DEA. We conclude that in the isolated perfused lungs: A is extensively taken up by the lungs of rats and rabbits; the uptake is not saturated by raising the concentrations over a 400-fold range; DEA is taken up more readily than A; and metabolism of neither compound is observed.