Phenytoin absorption in patients with ileojejunal bypass.

1 The absorption and elimination of phenytoin was studied after a 200 mg oral dose was administered to seven patients with ileojejunal bypass and nine control patients. 2 Analysis of the area under the plasma concentration time curve showed the absorption of phenytoin was decreased in the subjects with ileojejunal bypass (P less than 0.005). 3 The half life of elimination of the drug was shorter in the bypass group (15.1 h) than in the controls (17.8 h, P less than 0.05). 4 Subjects with an ileojejunal bypass receiving phenytoin are likely to require increased oral dosages to achieve an optimal plasma concentration. There is probably malabsorption of other poorly soluble drugs and parenteral therapy may be necessary to ensure adequate bioavailability.