Metabolism of phthalidyl theophylline in rat liver

Phthalidyl theophylline (PH-TH) in rat liver was metabolized by a hydrolase to theophylline (TH) and 2-carboxybenzaldehyde, and the latter was further metabolized to 2-hydroxymethylbenzoic acid by an nicotinamide adenine dinucleotide-dependent reductase. The hydrolase could be strongly inhibited by acetazolamide, therefore, urinary excretion of PH-TH metabolites was significantly retarded when PH-TH and acetazolamide were coadministered to rats. The results from in vivo experiments suggest that PH-TH was efficiently absorbed from the gastrointestines and metabolized extensively by the liver.