Amiodarone is a clinically effective antiarrhythmic drug shown to cause lung damage in humans and animals. While the mechanism of this pulmonary toxicity is unknown, it may be associated with the accumulation of amiodarone and its principal metabolite, desethylamiodarone, by alveolar macrophages. In the present study, characteristics of the uptake of these drugs by rat alveolar macrophages in vitro were examined. The alveolar macrophages were collected by pulmonary lavage from male Fischer 344 rats. Amiodarone and desethylamiodarone were incubated separately (2.5 microM) with the cells in culture for 1, 2, 4 and 18 hr. High performance liquid chromatography was used to measure drug uptake. At 1 and 2 hr, the uptake of desethylamiodarone by alveolar macrophages was significantly greater (P less than 0.05) than that of amiodarone, but over time, the accumulation of amiodarone began to approach that of desethylamiodarone and was not significantly different by 4 hr. To simulate a more physiological situation, plasma levels achieved in the adult male rat after 1 week of amiodarone treatment (150 mg/kg) were used. Amiodarone (1.95 micrograms/mL) and desethylamiodarone (0.80 microgram/mL) were added together into the cell culture. At 1 and 18 hr, the ratio of desethylamiodarone/amiodarone uptake was significantly greater (P less than 0.05) than in incubation medium containing no cells, indicating an enhanced uptake of desethylamiodarone. Metabolic inhibitors (KCN, 2,4-dinitrophenol, and ouabain) and other cationic, amphiphilic drugs (chlorcyclizine, chlorphentermine, and imipramine) were added individually to the cell cultures containing amiodarone or desethylamiodarone. During 1 hr of incubation, these agents had no effect in blocking the accumulation of amiodarone and desethylamiodarone in the cells. The efflux of amiodarone or desethylamiodarone was measured from cells following incubation for 4 hr with each drug. After this time, the medium was replaced with drug-free medium, and the cells were incubated for another 24 hr. Sixty-three percent of amiodarone was lost as compared to only 31% of desethylamiodarone over the 24-hr period (P less than 0.05). The results of this study are suggestive of a preferential uptake and retention of desethylamiodarone as compared to amiodarone. The accumulation of the drugs appears not to be due to active transport or associated with any carrier protein involved in the transport of other structurally-related compounds.