Antiepileptic effect of phenytoin is increased by all of the following except:
Sucralfate INTERACTIONS Phenobarbitone competitively inhibits phenytoin metabolism, while by enzyme induction both enhance each other's degradation. Cabamazepine and phenytoin increases each other's metabolism. * Valproate displaces protein bound phenytoin and decreases its metabolism: plasma level of unbound phenytoin Increases. * Chloramphenicol, isoniazid, cimetidine, dicumarol and warfarin inhibit phenytoin metabolism & can precipitate its toxicitiy. Phenytoin induces microsomal enzymes and increase degradation of steroids (failure of oral contraceptives), digitoxin, doxycycline, theophyline, * A number of acidic drugs displace it from protein binding sites but this also enhances phenytoin clearance - concentration of free form does not change much. * Sucralfate binds phenytoin in g.i. tract and decreases its absorption.
Isoniazid
Sucralfate
Cimetidine
Warfarin