DIFFERENTIAL ABSORPTION OF AMOXICILLIN FROM THE HUMAN SMALL AND LARGE-INTESTINE

Differences in extent of amoxicillin absorption from various regions o f the gastrointestinal tract were determined and compared with the sam e dose administered orally. Nine healthy men were intubated at a proxi mal (duodenum or jejunum) or distal (ileum or colon) site with use of a 15-foot double lumen nasointestinal tube. Amoxicillin solutions (375 mg in 120 ml water) were delivered on 2 successive days as a bolus or a 4-hour infusion. Subjects were reintubated at another site and amox icillin administration was repeated. Subjects with colonic intubation received only infusions. Finally, all subjects received an oral dose o f amoxicillin solution. Plasma samples were obtained at 16 time points over a 10-hour period and assayed for amoxicillin by use of an HPLC m ethod. Area under the concentration-time curve and the maximum plasma concentration were computed to evaluate amoxicillin absorption. Amoxic illin absorption was rate and site dependent in the gastrointestinal t ract. The drug was well absorbed in the duodenum and jejunum, with no significant differences in absorption when administered as a bolus or C-hour infusion, but absorption was decreased and rate dependent in th e ileum, where more drug was absorbed as an infusion compared with a b olus. Amoxicillin was unabsorbed when infused in all colonic regions.