Pharmacokinetics of bupropion and metabolites in plasma and brain of rats, mice, and guinea pigs

Recent reports indicate that bupropion, a novel non-tricyclic antidepressant, is metabolized differently in certain species of animals. To further define the disposition of bupropion, a study was done involving three species, the rat, mouse, and guinea pig, as animal models to evaluate bupropion metabolism. The pharmacokinetic profiles of bupropion and its major basic metabolites, BW 306U and BW A494U, were determined following the ip administration of 40 mg/kg bupropion to these animals. Pharmacokinetic profiles of the parent drug and metabolites from plasma and brain samples were obtained using a liquid chromatographic procedure. Further investigation of the reduced bupropion metabolite BW A494U was carried out by the ip administration of this metabolite to these animals and assaying the plasma and brain samples 90 min after dosing. Analysis of the pharmacokinetic data revealed that the rat quickly metabolized bupropion, but no basic metabolites accumulated. The mouse metabolized bupropion predominantly to BW 306U, whereas the guinea pig converted bupropion to reduced bupropion (BW A494U) as well as BW 306U. Brain/plasma ratios of bupropion among these animals did not vary significantly. However, both metabolites showed dramatic differences in their brain/plasma ratios among these species. When reduced bupropion (BW A494U) was injected, almost 3% of the plasma concentration of BW A494U was determined to be bupropion in the rat. Lesser amounts were converted in the mouse and guinea pig. Therefore, we have demonstrated that distinct differences exist in the metabolism of bupropion in various species of animals. The guinea pig, when compared to the rat or mouse, appears to constitute a model that most closely resembles that of human bupropion metabolism.