The demethylation of imipramine and clomipramine as apparent from their plasma kinetics

The demetylation of imipramine and clomipramine was studied after administration by different routes of single doses of clomipramine hydrochloride and multiple doses of clomipramine as well as imipramine hydrochloride. Five healthy volunteers received 1 mg of clomipramine hydrochloride/kg body weight as single oral and intramuscular doses on different occasions for the purpose of studying the plasma levels of clomipramine and the desmethylclomipramine formed. Desmethylclomipramine was found in the plasma in four of the subjects after oral intake but only in one subject after intramuscular injection. The peak levels of clomipramine were considerably higher after intramuscular than after oral administration. The half-lives of clomipramine after oral administration ranged from 11.6-35.8 h (M = 20.8 +/- 4.0) and after intramuscular administration from 20.1--39.6 h (M = 24.7 +/- 3.7). Twenty subjects received either imipramine or clomipramine both orally and intramuscularly during a period of 3 weeks in a crossover design. The plasma levels of imipramine and clomipramine and their demethylated metabolites desipramine and desmethylclomipramine were determined during the treatment. The ratio between the plasma level of the parent drug and its demethylated metabolite was on average twice as high during intramuscular as during oral treatment.