**5. Conclusions**

This comparative pharmacokinetic and tissue distribution study of compound K in rats and mice demonstrated the following processes (Figure 10). First, the plasma concentration of compound K in mice was significantly greater than that in rats and the fecal recovery of PPD over 48 h in rats was greater than that in mice although the differences in elimination and metabolism between the two species need further investigation. Second, the plasma compound K was quickly distributed into the liver and underwent biliary excretion rather than renal elimination. The distribution of compound K into other major organs (kidney, heart, lung, pancreas, and testis) was much lower than in the liver for both rats and mice. Third, compound K was metabolized into PPD by the intestinal microbiota and the intestinal PPD metabolite was reabsorbed in the systemic circulation of both rats and mice.

**Author Contributions:** Conceptualization, M.-K.C. and I.-S.S.; Investigation, J.-H.J., B.K., S.L., M.-K.C., S.J. and I.-S.S.; Writing—Original Draft Preparation, J.-H.J. and B.K.; Supervision, M.-K.C. and I.-S.S.; Writing—Review & Editing, M.-K.C. and I.-S.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.
