RT Journal Article SR Electronic T1 Elucidation of the Metabolic Pathways and the Resulting Multiple Metabolites of Almorexant, a Dual Orexin Receptor Antagonist, in Humans JF Drug Metabolism and Disposition JO Drug Metab Dispos FD American Society for Pharmacology and Experimental Therapeutics SP dmd.112.050120 DO 10.1124/dmd.112.050120 A1 Jasper Dingemanse A1 Petra Hoever A1 Matthias Hoch A1 Alexander Treiber A1 Winfried Wagner-Redeker A1 Tommaso Miraval A1 Gerard Hopfgartner A1 Kasra Shakeri-Nejad YR 2013 UL http://dmd.aspetjournals.org/content/early/2013/02/21/dmd.112.050120.abstract AB Almorexant, a tetrahydroisoquinoline derivative, is a dual orexin receptor antagonist with sleep-promoting properties in both animals and humans. This study investigated the disposition, metabolism, and elimination of almorexant in humans. After oral administration of a 200-mg dose of 14C-almorexant, almorexant was rapidly absorbed (Tmax = 0.8 h) and the apparent terminal t1/2 was 17.8 h. The radioactive dose was almost completely recovered with 78.0% of the administered radioactive dose found in feces and 13.5% in urine. Unchanged almorexant was not found in urine and represented 10% of the administered dose in feces. In total, 47 metabolites were identified of which 21 were shown to be present in plasma. There are 4 primary metabolites, the isomeric phenols M3 and M8, formed by demethylation, the aromatic isoquinolinium ion M5, formed by dehydrogenation, and M6, formed by oxidative dealkylation with loss of the phenylglycine moiety. Most of the subsequent products are formed by permutations of these primary metabolic reactions followed by conjugation of the intermediate phenols with glucuronic or sulfonic acid. The % of dose excreted in urine or feces for any of the metabolites did not exceed 10% of the administered radioactive dose nor did any of the metabolites represent more than 10% of total drug-related exposure.In conclusion, following rapid absorption, almorexant is extensively metabolized and excretion of metabolites in feces is the predominant route of elimination in humans.