An example of using off-line HPLC–MSC for profiling plasma metabolites
is displayed in Fig. 10.9. Plasma samples containing a total of 400–900 CPM of
radioactivity were injected. A minor metabolite (M3, 9 CPM, Fig. 10.9c),
approximately 3 % of the total radioactivity injected was clearly detected. The
percent distribution of all drug-related components in the plasma sample was
determined in the same analysis (Fig. 10.9). Furthermore, drug and metabolite
concentrations can be calculated by multiplying the percent distributions to the
concentrations of the total radioactivity in the corresponding plasma samples.
As a result, AUC0-8h values of the drug, M3 and M6 were obtained by
calculating their concentrations in multiple plasma samples collected from 0.5
to 8 h.
Interestingly, although the relative concentration (7.7 %) of M6 in the 8 h
dog plasma was much less than that (16.3 %) in the 1 h human plasma, the
AUC0-8hvalues of M6 in dogs and humans were comparable. Based on the
sensitivity provided by TopCount analysis (Table 10.1), samples containing
FIGURE 10.9 Representative plasma metabolite profiles of a radiolabeled drug
candidate in rats (a), dogs (b), and humans (c). The pooled plasma samples from
radiolabeled ADME studies after an oral administration were collected around the
maximum concentration of the drug. The radioactivity profiles were determined by off-
line HPLC–TopCount (four functions per min and 10 min counting time).
Approximately, 400–9000 DPM of radioactivity was injected.
APPLICATION OF NEW RADIOCHROMATOGRAPHY TECHNIQUES 307