The in vitro metabolism of desglymidodrine, an active metabolite of prodrug midodrine by human liver microsomes.

The human cytochrome P450 (CYP) isoforms catalyzing the oxidation metabolism of desglymidodrine (DMAE), an active metabolite of midodrine, were studied. Recombinant human CYP2D6, 1A2 and 2C19 exhibited appreciable catalytic activity with respect to the 5'-O-demethylation of DMAE. The O-demethylase activity by the recombinant CYP2D6 was much higher than that of other CYP isoforms. Quinidine (a selective inhibitor of CYP2D6) inhibited the O-demethylation of DMAE in pooled human microsomes by 86%, while selective inhibitors for other forms of CYP did not show any appreciable effect. Although the activity of CYP2D6 was almost negligible in the PM microsomes, the O-demethylase activity of DMAE was found to be maintained by about 25% of the pooled microsomes. Furafylline (a selective inhibitor of CYP1A2) inhibited the M-2 formation in the PM microsomes by 57%. The treatment of pooled microsomes with an antibody against CYP2D6 inhibited the formation of M-2 by about 75%, whereas that of the PM microsomes did not show drastic inhibition. In contrast, the antibody against CYP1A2 suppressed the activity by 40 to 50% in the PM microsomes. These findings suggest that CYP2D6 have the highest catalytic activity of DMAE 5'-O-demethylation in human liver microsomes, followed by CYP1A2 to a small extent.