Gastrointestinal Absorption of Chlorothiazide : Evaluation of a Method Using Salicylazosulfapyridine and Acetaminophen as the Marker Compounds for Determination of the Gastrointestinal Transit Time in the Dog

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Gastrointestinal absorption properties of chlorothiazide was investigated in dogs by a double-marker method using acetaminophen and salicylazosulfapyridine as the markers.The mean absorption time of acetaminophen (MAT_AAP) and the time for first appearance of sulfapyridine in plasma (TFA_SP) were used for the assessment of gastric emptying and oro-colonic transit times, respectively. Chlorothiazide absorption efficiency was increased by pretreatment with atropine sulfate. There was a good correlation between MAT_AAP and the extent of bioavailability of chlorothiazide, however, there was no correlation between TFA<SP> and the extent of bioavailability of the drug. These results indicate that chlorothiazide absorption takes place primarily in a limited segment of the upper small intestine, supporting the assumption reported previously. This double-marker method seems to be a useful tool for the investigation of the relationship between drug absorption and its gastrointestinal transit.