In Vivo Absorption of Phenytoin from Rat Small Intestine and its Inhibition by Phlorizin

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Abstract
In vivo absorption of phenytoin from the small intestine was studied by an in vivo closed segment technique. Phenytoin in concentrations of 1000, 2000 and 4000 .mu.mol/l was administered in dissolved form. Polythylene glycol 4000 was used as a non-absorbable marker. The concentrations of phenytoin in the intestinal lumen, in the mucosa and in cardiac blood were measured by spectrophotometry and by gas chromatography. Phenytoin was absorbed very rapidly, and the proportion absorbed increased with increasing dose. During the first 10 min .apprx. 85% of the largest dose but only 25% of the smallest dose was absorbed. The phenytoin concentration in mucosa and serum increased in an analogous way; maximum values were seen within the first 10 min. The concentrations in mucosa and serum were dose dependent during the first 10 min. Phlorizin 0.01 and 1 mmol/l significantly reduced the transfer of phenytoin (4000 and 2000 .mu.mol/l) from the gut lumen to the mucosa. No inhibition was seen when the initial phenytoin dose was 1000 .mu.mol/l. Apparently an active transport mechanism, sensitive to phlorizin, is involved in the intestinal absorption of phenytoin in the rat.