Urinary excretion of 4-hydroxyamphetamine and amphetamine in male and female Sprague-Dawley and Dark Agouti rats following multiple doses of amphetamine.

Previous studies have demonstrated that the cytochrome P450 2D subfamily is involved in the 4-hydroxylation of amphetamine in the rat. These studies followed urinary levels of 4-hydroxyamphetamine and amphetamine after a single dose of amphetamine given with the P450 2D inhibitor quinidine or in P450 2D-deficient Dark Agouti (DA) rats. Multiple doses of amphetamine are used by humans and in experimental neurotoxicity studies of amphetamine. We hypothesized that the elimination of amphetamine (as opposed to 4-hydroxyamphetamine) will remain elevated in the DA rat after multiple doses, implying that no alternative pathway is induced to compensate for reduced 4-hydroxylation. Male and female Sprague-Dawley (SD) and DA rats were given daily i.p. injections of 5 mg/kg amphetamine for 5 days. Urine was collected at 12-h intervals and analyzed by HPLC for the presence of amphetamine and 4-hydroxyamphetamine. The amount of amphetamine detected in the urine remained elevated with a corresponding reduction of 4-hydroxyamphetamine in the DA rats when compared to SD rats over the entire time course. This reduction in 4-hydroxyamphetamine was greater in female than male DA rats; no difference was found between male and female SD rats. At the dose used, amphetamine did not increase with time and total amphetamine and 4-hydroxyamphetamine excreted by all rats was not different, implying no accumulation of amphetamine. These results suggest that no alternative pathway is induced following multiple doses of amphetamine in normal SD or P450 2D deficient DA rats.