Comment on: "In vitro - In vivo metabolism and pharmacokinetics of picroside I and II using LC-ESI-MS method"

The letter highlights the difference in the pharmacokinetic profile of picroside II in Sprague-Dawley rats as reported by Upadhyay et al., in two separate studies. Both the studies have been conducted by the same author, in the same laboratory set-up, using the similar animal species and sex as well as the same dose level of kutkin (Dose: 100 mg/kg bodyweight, which was equivalent to 45 mg/kg of picroside I and 55 mg/kg of picroside II). However, the Cmax and AUC(0-t) observed in the first study were 9-fold and 5-fold higher, respectively, as compared to the recently reported study. The only difference between these two studies was the instrument used for analysing the plasma samples. In the first study, the analyses of the plasma samples were done using HPLC-UV whereas the second study used LC-ESI-MS system for plasma sample analysis. The pharmacokinetic parameters shall not change significantly with the change in analytical instrument. In my opinion, the probable cause for the observed higher Cmax and AUC(0-t) values in the first study may be due to the interference of some metabolite(s)/impurity that got eluted at the same retention time as that of picroside II and contributed to the higher values. The future prospects shall focus on identifying the metabolite(s)/impurity that have co-eluted with picroside II during initial HPLC-UV analysis and contributed to the higher Cmax and AUC(0-t) values by performing parallel analysis of plasma samples using HPLC-PDA and LC-ESI-MS. (C) 2016 Elsevier Ireland Ltd. All rights reserved.