This paper investigated the pharmacokinetics and biotransformation of mirtazapine in healthy human volunteers. The results showed that the area under the plasma drug concentration-time curve (AUC) of mirtazapine in human plasma appeared to be three times higher than the AUC of demethylmirtazapine. As mirtazapine is marketed as a racemic mixture and both enantiomers possess pharmacological properties essential for the overall activity of the racemate, the pharmacokinetics of mirtazapine were examined and appeared to be enantioselective. The R(-)-enantiomer showed the longest elimination half-life from plasma. This was ascribed to the preferred formation of a quaternary ammonium glucuronide of the R(-)-enantiomer. This glucuronide may be deconjugated, leading to a further circulation of the parent compound, thus causing a prolongation in the elimination half-life. The S(+)-enantiomer was preferentially metabolised into an 8-hydroxy glucuronide. Other metabolic transformation pathways found for mirtazapine were demethylation and N-oxidation. Mirtazapine was extensively metabolised and almost completely excreted in the urine (over 80%) and faeces within a few days after oral administration.

1. The biotransformation and excretion of the antidepressant mianserin were studied after oral administration of the labelled drug to rats, mice, rabbits, guinea pigs and humans. Mianserin was well absorbed and almost completely metabolized in all five species. 2. Major metabolic pathways of mianserin were p-oxidation of the N-substituted aromatic ring followed by conjugation, and oxidation and demethylation of the N-methyl moiety, followed by conjugation. Direct conjugation of the N-methyl moiety was observed as a metabolic pathway specific for man. 3. Conjugated metabolites were isolated by h.p.l.c. and identified by 1H-n.m.r. and FAB spectrometry. Novel metabolites such as an N-O-glucuronide in the guinea pig and an N-sulphonate in rat and guinea pig, were identified using these techniques. A quaternary N-glucuronide was found only in man.

ABSTRACT: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 ϳ90%, with ϳ50% appearing in urine and ϳ40% 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, Ndesmethylasenapine, and asenapine 11-O-sulfate. In addition to the parent compound, asenapine, the principal excretory metabolite was asenapine N ؉ -glucuronide. Other excretory metabolites were Ndesmethylasenapine-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.

Previously published metabolites were confirmed in this study and additional metabolites were identified, two of which are discussed to illustrate the advantages of the workflow.

To support the practical implementation of the International Council for Harmonisation (ICH) Q3D guideline, which describes a risk-based approach to the control of elemental impurities in drug products, a consortium of pharmaceutical companies has established a database to collate the results of analytical studies of the levels of elemental impurities within pharmaceutical excipients. This database currently includes the results of 26,723 elemental determinations for 201 excipients and represents the largest known, and still rapidly expanding, collection of data of this type. Analysis of the database indicates good coverage of excipients relevant to real-world drug product formulations and tested element profiles consistent with ICH Q3D recommendations. The database includes the results from multiple analytical studies for an excipient and thus incorporates within it an indication of both excipient supplier and batch-to-batch variability as well as any variability associated with the different testing organizations and methods employed. The data confirm the findings of earlier smaller studies that elemental impurity concentrations in excipients are generally low and when used in typical proportions in formulated drug products are unlikely to pose a significant patient safety risk. The database is now in active use as one line of evidence in ICH Q3D risk assessments.