Metabolism and excretion of asenapine in healthy male subjects.

The metabolism and excretion of asenapine [(3aRS,12bRS)-5-chloro-2-methyl-2,3,3a,12b-tetrahydro-1H-dibenzo[2,3:6,7]-oxepino [4,5-c]pyrrole (2Z)-2-butenedioate (1:1)] were studied after sublingual administration of [(14)C]-asenapine to healthy male volunteers. Mean total excretion on the basis of the percent recovery of the total radioactive dose was ∼90%, with ∼50% appearing in urine and ∼40% excreted in feces; asenapine itself was detected only in feces. Metabolic profiles were determined in plasma, urine, and feces using high-performance liquid chromatography with radioactivity detection. Approximately 50% of drug-related material in human plasma was identified or quantified. The remaining circulating radioactivity corresponded to at least 15 very polar, minor peaks (mostly phase II products). Overall, >70% of circulating radioactivity was associated with conjugated metabolites. Major metabolic routes were direct glucuronidation and N-demethylation. The principal circulating metabolite was asenapine N(+)-glucuronide; other circulating metabolites were N-desmethylasenapine-N-carbamoyl-glucuronide, N-desmethylasenapine, and asenapine 11-O-sulfate. In addition to the parent compound, asenapine, the principal excretory metabolite was asenapine N(+)-glucuronide. Other excretory metabolites were N-desmethylasenapine-N-carbamoylglucuronide, 11-hydroxyasenapine followed by conjugation, 10,11-dihydroxy-N-desmethylasenapine, 10,11-dihydroxyasenapine followed by conjugation (several combinations of these routes were found) and N-formylasenapine in combination with several hydroxylations, and most probably asenapine N-oxide in combination with 10,11-hydroxylations followed by conjugations. In conclusion, asenapine was extensively and rapidly metabolized, resulting in several regio-isomeric hydroxylated and conjugated metabolites.

The in vivo metabolism of tibolone in animal species.

The in vivo tissue distribution and metabolism of tibolone was studied in different animals to further investigate the compound's tissue-specificity. Tibolone's metabolism was studied in vivo in rats and rabbits by administration of [16-3H]-tibolone and the metabolic pattern was determined in urine and faeces after oral administration to female rats and dogs. The main excretory pathway was found to be excretion in the faeces. Important phase-I metabolic routes were the reduction of the 3-keto to the 3a- or 3beta-hydroxy functions with a preference for 3alpha-OH in rats and for 3beta-OH in dogs. To a lesser extent, hydroxylation reactions at C2 and C7, and a shift of the delta5(10)-double bond to a delta4(5)-position also occurred. The main phase-II metabolic route was sulphate conjugation of the hydroxyl groups at C3 and C17. Since the oxidation reactions form only a minor part of the metabolism of tibolone, it is concluded that the cytochrome P450 enzymes do not play an important role in tibolone's metabolism. For both phases, quantitative differences were found between the species. In human similar metabolites are found. Profiling of the target organs in female rats and rabbits showed a tissue-specific distribution of metabolites. The majority of the metabolites existed as sulphate conjugates and no glucuronidated conjugates were observed. The same metabolites were found in both the circulation and the tissues. However, different tissues had quantitatively different metabolic profiles.

Selective tissue distribution of tibolone metabolites in mature ovariectomized female cynomolgus monkeys after multiple doses of tibolone.

Tibolone is a selective tissue estrogenic activity regulator (STEAR). In postmenopausal women, it acts as an estrogen on brain, vagina, and bone, but not on endometrium and breast. Despite ample supporting in vitro data for tissue-selective actions, confirmative tissue levels of tibolone metabolites are not available. Therefore, we analyzed tibolone and metabolites in plasma and tissues from six ovariectomized cynomolgus monkeys that received tibolone (0.5 mg/kg/day by gavage) for 36 days and were necropsied at 1, 1.25, 2.25, 4, 6, and 24 h after the final dose. The plasma and tissue levels of active, nonsulfated (tibolone, 3alpha-hydroxytibolone, 3beta-hydroxytibolone, and Delta(4)-tibolone), monosulfated (3alpha-sulfate,17beta-hydroxytibolone and 3beta-sulfate,17beta-hydroxytibolone), and disulfated (3alpha,17beta-disulfated-tibolone and 3beta,17betaS-disulfated-tibolone) metabolites were measured by validated gas chromatography with mass spectrometry and liquid chromatography with tandem mass spectrometry. Detection limits were 0.1 to 0.5 ng/ml (plasma) and 0.5 to 2 ng/g (tissues). In brain tissues, estrogenic 3alpha-hydroxytibolone was predominant with 3 to 8 times higher levels than in plasma; levels of sulfated metabolites were low. In vaginal tissues, major nonsulfated metabolites were 3alpha-hydroxytibolone and the androgenic/progestagenic Delta(4)-tibolone; disulfated metabolites were predominant. Remarkably high levels of monosulfated metabolites were found in the proximal vagina. In endometrium, myometrium, and mammary glands, levels of 3-hydroxymetabolites were low and those of sulfated metabolites were high (about 98% disulfated). Delta(4)-Tibolone/3-hydroxytibolone ratios were 2 to 3 in endometrium, about equal in breast and proximal vagina, and 0.1 in plasma and brain. It is concluded that tibolone metabolites show a unique tissue-specific distribution pattern explaining the tissue effects in monkeys and the clinical effects in postmenopausal women.

Pharmacokinetic parameters of tibolone and metabolites in plasma, urine, feces, and bile from ovariectomized cynomolgus monkeys after a single dose or multiple doses of tibolone.

Levels of nonsulfated and sulfated tibolone metabolites were determined in plasma, urine, and feces from six ovariectomized, mature female cynomolgus monkeys after a single dose and multiple p.o. doses (including bile) of tibolone using validated gas chromatography/mass spectrometry and liquid chromatography/tandem mass spectrometry assays. In plasma, the predominant nonsulfated metabolite after single and multiple dosing was the estrogenic 3alpha-hydroxytibolone; levels of the estrogenic 3beta-hydroxytibolone were 10-fold lower and of progestagenic/androgenic Delta(4)-tibolone, 5-fold lower. Tibolone was undetectable. The predominant sulfated metabolite was 3alphaS,17betaS-tibolone; levels of 3betaS,17betaS-tibolone were about 2-fold lower, and monosulfated 3-hydroxymetabolites were about 10-fold lower. After multiple doses, areas under the curve of nonsulfated metabolites were lower (2-fold), and those of sulfated metabolites were 25% higher. In plasma, >95% metabolites were disulfated. In urine, levels of all the metabolites after single and multiple doses were low. After a single dose, high levels of 3beta-hydroxytibolone and the 3-monosulfated metabolites (3betaS,17betaOH-tibolone and 3alphaS,17betaOH-tibolone) were found in feces. After multiple dosing, 3alpha-hydroxytibolone increased, and the ratio of 3alpha/3beta-hydroxytibolone became about 1. The predominant sulfated metabolite was 3alphaS,17betaS-tibolone. Levels of all the metabolites in feces were higher after multiple doses than after a single dose. Levels of nonsulfated and 3-monosulfated metabolites were higher in feces than in plasma. Bile contained very high metabolite levels, except monosulfates. This may contribute to the metabolite content of the feces after multiple doses. 3beta-Hydroxytibolone and 3alphaS,17betaS-tibolone predominated. In conclusion, tibolone had different metabolite patterns in plasma, urine, feces, and bile in monkeys. The bile contributed to the metabolite pattern in feces after multiple doses. The major excretion route was in feces.

The in vivo human metabolism of tibolone.

In vivo metabolism of tibolone was studied in three healthy postmenopausal volunteers after daily oral administration of 2.5 mg of tibolone for 5 days and a single dose of 2.5 mg approximately equal 555 kBq of [(14)C]tibolone on day 6. The 0- to 192-h recovery of radioactivity in urine and feces was 31.2 +/- 10.5 and 53.7 +/- 5.1%, respectively. Total 0- to 192-h recovery ranged from 78.5 to 94.2% of the dose and averaged 84.9%. Metabolites were putatively identified using high-pressure liquid chromatography in plasma, urine, and feces. The most important phase I metabolic reactions were reduction of the 3-keto group to 3alpha- and 3beta-hydroxy metabolites, a shift of the Delta(5(10))-double bond to a Delta(4(5))-double bond, a reduction of the Delta(4(5))-double bond to 5alpha,10-dihydro or 5beta,10-dihydro metabolites, and hydroxylation at C2 and C7. The most important phase II metabolic reaction is sulfation of the C17 hydroxy group of tibolone and sulfation of the C3 hydroxy groups. In the circulation, over 75% of tibolone and its metabolites are present in the sulfated form. Local metabolism and local sulfatases may contribute to the tissue-specific activity. Using human microsomes, tibolone, 3alpha-hydroxy tibolone, 3beta-hydroxy tibolone, and Delta(4)-tibolone appeared to be at least 50-fold less potent inhibitors of CYP1A2, CYP2C9, CYP2E1, and CYP3A4 compared with enzyme-selective inhibitors. Tibolone and its metabolites, therefore, are not likely to play a clinically significant role at the level of these cytochrome P450 enzymes with regard to the metabolism of coadministered drugs.