Page - (000122) - in Biomedical Chemistry: Current Trends and Developments

important to highlight that the bioanalytic methodologies employed to quantify the drugs were at least partially validated in order to confirm their acceptability for each specific compound (Table 2.1.6). 2.1.4.2 Bioanalytic Support of In Vivo ADME/Pharmacokinetic Studies As depicted in Table 2.1.6, most of the in vitro techniques implemented to evaluate the ADME of NCEs are complemented with non-clinical pharmacokinetic studies performed in rodent animals (mice or rats). As expected, the major objectives include the determination and evaluation of the extent and rate of absorption (AUC, Cmax and tmax), distribution (Vd), clearance and duration of exposure (t1/2) of a drug and its metabolites after oral and/or iv administration. UV, MS and MS/MS are the major detection methods used for the quantification of parent drug in biological matrices, but MS and MS/MS have been more frequently used and seem to be preferable for relating metabolite response with that of the parent drug due to higher accuracy and sensitivity. In fact, identification and structure elucidation of the metabolites previously obtained in vitro must be confirmed in non-clinical and then in clinical studies. Similarly, the monitoring of metabolite exposure in non-clinical species and humans are also mandatory and therefore widely investigated in current practice (Table 2.1.6) (Zhu et al., 2009). These results are crucial since, according to the FDA guidelines on MIST and DDI, the relative exposure of metabolite can be obtained from the metabolite profiling of time-averaged AUC-pooled human plasma samples from multiple ascending dose studies. It is interesting to note that similar chromatographic conditions can be employed to investigate the pharmacokinetics of NCEs both in vitro and in vivo, although detection may vary depending on the study objectives and the DDD stage. For instance, Fortuna et al. (2012, 2013) employed a validated HPLC-UV technique to firstly determine the in vitro apparent permeability of nine derivatives of carbamazepine through mice intestine and secondly characterize the plasma and brain pharmacokinetics after oral administration to mice. To attain those objectives, a C18 column was used (Table 2.1.6) and the parent