The kinetics of imipramine-N-oxide in rats.

Rats were given imipramine-N-oxide as single intramuscular injection and then as repeated oral doses. Imipramine-N-oxide and the metabolites imipramine and desipramine were analysed in the blood cells, plasma and brain tissue. The concentration of imipramine-N-oxide increased simultaneously in the brain and blood, reaching a peak 45 minutes after a single dose. Imipramine was the quantitatively predominant metabolite in the blood cells and brain, while desipramine reached a higher concentration than imipramine in the plasma. Samples taken at different times after oral doses during continuous treatment showed fairly constant concentrations of imipramine-N-oxide and desipramine in the brain, whereas the concentration of imipramine was more fluctuating.