RT Journal Article
SR Electronic
T1 Disposition and Biotransformation of the Antipsychotic Agent Olanzapine in Humans
JF Drug Metabolism and Disposition
JO Drug Metab Dispos
FD American Society for Pharmacology and Experimental Therapeutics
SP 81
OP 93
VO 25
IS 1
A1 Kelem Kassahun
A1 Edward Mattiuz
A1 Eldon Nyhart, Jr.
A1 Boyd Obermeyer
A1 Todd Gillespie
A1 Anthony Murphy
A1 R. Michael Goodwin
A1 David Tupper
A1 J. Thomas Callaghan
A1 Louis Lemberger
YR 1997
UL http://dmd.aspetjournals.org/content/25/1/81.abstract
AB Disposition and biotransformation of the new antipsychotic agent olanzapine (OLZ) were studied in six male healthy volunteers after a single oral dose of 12.5 mg containing 100 μCi of [14C]OLZ. Biological fluids were analyzed for total radioactivity, the parent compound (GC/MS), and metabolites (electrospray LC/MS and LC/MS/MS). Mean radiocarbon recovery was ∼87%, with 30% appearing in the feces and 57% excreted in the urine. Approximately half of the radiocarbon was excreted within 3 days, whereas >70% of the dose was recovered within 7 days of dosing. Circulating radioactivity was mostly restricted to the plasma compartment of blood. Mean peak plasma concentration of OLZ was 11 ng/ml, whereas that of radioactivity was 39 ng eq/ml. Mean plasma terminal elimination half-lives were 27 and 59 hr, respectively, for OLZ and total radioactivity. With the help of NMR and MS data, a major metabolite of OLZ in humans was characterized as a novel tertiaryN-glucuronide in which the glucuronic acid moiety is attached to the nitrogen at position 10 of the benzodiazepine ring. Another N-glucuronide was detected in urine and identified as the quaternary N-linked 4′-N-glucuronide. Oxidative metabolism on the allylic methyl group resulted in 2-hydroxymethyl and 2-carboxylic acid derivatives of OLZ. The methyl piperazine moiety was also subject to oxidative attack, giving rise to the N-oxide and N-desmethyl metabolites. Other metabolites, including the N-desmethyl-2-carboxy derivative, resulted from metabolic reactions at both the 4′ nitrogen and 2-methyl groups. The 10-N-glucuronide and OLZ were the two most abundant urinary components, accounting for ∼13% and 7% of the dose, respectively. In fecal extracts, the only significant radioactive HPLC peaks were due to 10-N-glucuronide and OLZ representing, respectively, ∼8% and 2% of the administered dose. Semiquantitative data obtained from plasma samples from subjects given [14C]OLZ suggest that the main circulating metabolite is 10-N-glucuronide. Thus, OLZ was extensively metabolized in humans via N-glucuronidation, allylic hydroxylation,N-oxidation, N-dealkylation and a combination thereof. The 10-N-glucuronidation pathway was the most important pathway both in terms of contribution to drug-related circulating species and as an excretory product in feces and urine. The American Society for Pharmacology and Experimental Therapeutics