[Gastrointestinal absorption of nitrofurantoin: evaluation of a newly developed method for determination of the gastrointestinal transit time in dogs].

The relationship between the oral absorption and gastrointestinal transit time of nitrofurantoin was investigated in dogs by the double-marker method using acetaminophen and salicylazosulfapyridine as markers. The extent of bioavailability of nitrofurantoin gave correlations with both gastric emptying time and small intestinal transit time. The results indicate that the slower the passage from the stomach into the small intestine and/or the longer the residence time in the small intestine, the oral absorption efficiency of nitrofurantoin increases. These observations were consistent with the reported findings from in situ absorption study in rats and intestinal intubation study in humans, respectively. Moreover, it was clarified that small intestinal transit time is the most important determinant of absorption of nitrofurantoin, since the good correlation was observed between the small intestinal transit time and the extent of bioavailability. The double-marker method appears consequently to be useful tool for the determination of the gastrointestinal transit time in dogs.