Isolation and identification of major metabolites of rifalazil in mouse and human

1. Three metabolites of rifalazil have been isolated from dog urine and identified as 25-deacetyl-rifalazil, 30-hydroxy-rifalazil and 25-deacetyl-30-hydroxy-rifalazil. In the current study major metabolites of rifalazil in mouse and human were isolated and identified, and their antimicrobial activities determined. 2. Urinary excretion of rifalazil and its metabolites in six mouse strains, CD-1 (ICR), BALB/c, C57BL/6, C3H/He, DBA/2 and CBA/J, was examined. Two major metabolites were detected in mouse urine obtained after several oral doses, and the proportion of rifalazil metabolites against total urinary excretion varied over a 2-fold range (4.8-8.7 %) in the different mouse strains. 3. One of two major metabolites in mouse urine was 25-deacetyl-rifalazil and the other was unknown: it was isolated from mouse urine and identified by ms and H-1- and C-13-nmr as 32-hydroxy-rifalazil. 4. In human, two major metabolites of rifalazil were detected in urine obtained after administration of a single oral dose. These metabolites were also produced by incubation of rifalazil with pooled human liver microsomes, and identified by lc/ms and lc/ms/ms as 25-deacetyl-rifalazil and 32-hydroxy-rifalazil. 5. The antimicrobial activities of 32-hydroxy-rifalazil against Gram-positive bacteria and mycobacteria were similar with those of the parent compound.