Incurred sample stability of ASP3258 in the presence of its acyl glucuronide

The acyl glucuronide (AG) of ASP3258 was abundant in incurred monkey samples, and because an AG generally back-converts to its aglycone, accurate quantification of ASP3258 in monkey plasma was a challenge. To prevent the back-conversion of ASP3258-AG, cooling and acidification were incorporated during sample collection, storage, and extraction. To demonstrate that the AG did not affect the determination of ASP3258, the present study used incurred samples to examine whole blood stability, short-term stability, freeze-thaw stability, frozen stability, and stability during extraction. The concentration changes were within −11.4% to 15.0% compared with a reference value and were therefore judged acceptable. The present study presents a detailed account of test items, a reference value, sample numbers, sample selection, and an equation for assessment in the incurred sample stability tests. This bioanalytical method was applied successfully to a study of the toxicokinetics of ASP3258 in monkeys.