Metabolism of doxophylline by rat liver microsomes

The metabolic transformation of the bronchospasmolytic agent doxophylline (2-(7'-theophyllinemethyl)-1,3-dioxolane) was studied in vitro with phenobarbital-induced rat liver microsomal fraction containing the NADPH-generating system. Doxophylline was poorly metabolized as 95% of the recovered material was parent compound. The major metabolite resulted: 2'-hydroxyethyl ester of theophylline acetic acid. This was an unusual metabolite which possibly arose from dioxolane C2 enzymatic oxydation and subsequent ring opening. Theophylline was a minor metabolite. The per cent ratio of the two metabolites was 4:1; as we did not detected the presence of any compounds formed from N-demethylation, we concluded that doxophylline underwent a regiospecific metabolism on the N⁷ side chain.