Carbamazepine increases phenytoin serum concentration and reduces phenytoin clearance

Abstract

Addition of carbamazepine to phenytoin monotherapy resulted in the following significant (p less than 0.05) changes: (1) increased mean phenytoin serum concentration; (2) decreased phenytoin clearance, due to decreased production of phenytoin dihydrodiol and p-hydroxyphenyl-phenylhydantoin; (3) increased phenytoin elimination half-life; and (4) increased drug-related toxicity. Close monitoring is required after addition of carbamazepine to phenytoin.