Metabolite characterization of ambrisentan, in in vitro and in vivo matrices by UHPLC/QTOF/MS/MS: Detection of glutathione conjugate of epoxide metabolite evidenced by in vitro GSH trapping assay.

The focus of the present study is on in vitro and in vivo metabolite identification of ambrisentan (AMBR) a selective endothelin type - A (ETA) receptor antagonist using quadruple time-of-flight mass spectrometry (QTOF/MS). in vitro metabolism study was conducted by incubating AMBR in rat liver microsomes (RLM), rat and human liver S9 fractions. In vivo study was carried out through the collection of urine, faeces and plasma samples at various time points after oral administration of AMBR in suspension form at a dose of 25 mg/kg to six male Sprague - Dawley (SD) rats. The samples were prepared using an optimized sample preparation techniques involving protein precipitation (PP), freeze liquid extraction (FLE) and solid phase extraction (SPE). The extracted samples were further concentrated and analyzed by developing a sensitive and specific liquid chromatography-mass spectrometry (LC-MS) method. A total of seventeen metabolites were identified in in vivo samples which includes hydroxyl, demethylated, demethoxylated, hydrolytic, decarboxylated, epoxide and glucuronide metabolites. Most of the metabolites were observed in faeces and urine matrices and few were observed in the plasma matrix. Only ten metabolites were identified in in vitro study which was commonly observed in in vivo study. The detailed structural elucidation of all the metabolites was done using UHPLC/QTOF/MS/MS in combination with accurate mass measurements. The toxicity profile of AMBR and its metabolites were predicted using TOPKAT software. In addition, a mass spectrometric method was developed for the detection and characterization of GSH-trapped reactive epoxide metabolitein human liver S9 fraction supplemented with glutathione (GSH) as trapping agent.

Stability-Indicating Reversed-Phase UHPLC Method Development and Characterization of Degradation Products of Almotriptan Maleate by LC-QTOF-MS/MS.

Almotriptan maleate (ALMT), a highly selective 5-hydroxy tryptamine 1B/1D (5-HT1B/1D) receptor agonist used in the treatment of migraine headache was subjected to various ICH (Q1A (R2)) specified guidelines. The drug underwent significant degradation under hydrolytic (acid, base and neutral), oxidative and photolytic stress conditions, while it was stable under thermal stress condition. A total of seven significant degradation products (DPs) were obtained. A simple, selective and reliable UPLC method has been developed for the separation of ALMT and its DPs using Acquity UPLC HSS Cyano (100 × 2.1 mm, 1.8 µm) column with mobile phase consisting of ammonium acetate (10 mM, pH 4.4) buffer and acetonitrile in gradient elution mode. Chromatographic analysis was performed at a flow rate of 0.3 mL/min using a PDA detector at a wavelength of 230 nm. All the DPs (DP-1 to DP-7) were characterized using UHPLC-ESI-QTOF based on mass fragmentation pattern and accurate m/z values. The developed UPLC method was validated in terms of specificity, linearity, precision and accuracy. The developed stability-indicating method helps in quantification of drug in the presence of DPs.