Interference of a sulfate conjugate in quantitative liquid chromatography/tandem mass spectrometry through in-source dissociation

Discovery of a novel trimebutine metabolite and its impact on N-desmethyltrimebutine quantification by LC–MS/MS

Hélène Montpetit has a Bachelor of Science in Biochemistry from the University du Québec at Montreal. For the past 15 years, she has worked in the bioanalysis field in CROs environment as well as in a big Pharma. She currently holds a position as scientific reviewer in the method development group at Algorithme Pharma.

Background: A failure in incurred sample reanalysis (ISR) for N-desmethyltrimebutine (NDMT), during the analysis of a trimebutine-containing drug GIC-1001 Phase I study, led to the discovery of a never-before reported metabolite of trimebutine. Results: A positive bias for NDMT during the ISR and post-reconstitution stability evaluations indicated the presence of an unstable metabolite of NDMT. Precursor ion scans performed on freshly extracted samples enabled the identification of this metabolite to be the NDMT glucuronide conjugate and its fragmentation pattern suggested that the glucuronide moiety was attached at the N-terminal of NDMT. Conclusions: An acidification step was introduced in the extraction procedure to completely hydrolyze the glucuronide and measure the total NDMT in plasma, rendering this method a successful fit-for-purpose assay.

A practical approach to reduce interference due to in-source collision-induced dissociation of acylglucuronides in LC–MS/MS

Background: In LC–MS/MS, glucuronide conjugated metabolites may convert back to the parent drug due to in-source collision-induced dissociation (CID). Results: During the bioanalysis of naproxen, it was noticed that naproxen acylglucuronide exhibited intense in-source CID to the naproxen [M+H]+ ion under positive ESI. However, no in-source CID of the acylglucuronide to the naproxen [M+NH4]+ adduct was observed. Furthermore, absolutely no in-source CID was detected under negative ESI. This phenomenon was not only observed for naproxen acylglucuronide but for eight other acylglucuronides compounds. Conclusion: We have shown that monitoring the parent drug [M-H]- or [M+NH4]+ whenever possible could be an easy approach used by bioanalytical scientists to minimize the impact of in-source CID of acylglucuronides to the parent drug.

Potentially new isobaric metabolite of fluvastatin observed by LC–MS/MS during incurred sample analysis

Background: Fluvastatin (Lescol®) is a racemic mixture of two erythro stereoisomers and metabolizes into two threo stereoisomers. A method was developed to chromatographically separate fluvastatin from its threo isomers to support a bioequivalence study. Results: During incurred samples analysis, an additional peak sharing the same mass transition as fluvastatin was observed and interfered with fluvastatin’s quantification. Consequently, the chromatographic conditions were modified in order to resolve fluvastatin and the interference. Extensive evaluations were performed to ensure that the interference is not a degradation product generated during sample processing. Conclusion: An isobaric compound of fluvastatin was discovered, which required chromatographic separation from fluvastatin to obtain a reliable bioanalytical method. The investigation performed suggests that the interference is produced in vivo and is a possible metabolite of fluvastatin.

Impact of oxcarbazepine sulfate metabolite on incurred sample reanalysis and quantification of oxcarbazepine

Background: Recently, incurred sample reanalysis (ISR) has become a requirement in bioanalysis. The general guidance recommends investigating ISR failure to evaluate the suitability of an analytical method. In the case of acceptable ISR evaluation, there were no precise recommendations for further testing when sporadic values were obtained. Results: The ISR evaluation performed during a bioequivalence study for the anticonvulsant drug oxcarbazepine showed acceptable ISR results, but one particular chromatographic anomaly led to a thorough investigation. The finding of these tests showed that an oxcarbazepine phase II metabolite occasionally co-eluted with the drug and impacted oxcarbazepine’s quantitation through in-source conversion. Conclusion: This paper demonstrates the necessity of rigorous interpretation of ISR results and close monitoring of all subject sample results.