LAMOTRIGINE AND PHENYTOIN
Phenytoin has been associated with reduced lamotrigine serum levels (by almost two- thirds in one study). Lamotrigine has no effect on phenytoin levels.
Phenytoin (and therefore probably fosphenytoin) induces the metabolism of lamotrigine, and the recommended starting dose and long-term maintenance dose of lamotrigine in patients already taking phenytoin is twice that of patients receiving lamotrigine monotherapy. However, note that if they are also taking valproate in addition to phenytoin, the lamotrigine dose should be reduced.
Phenytoin (and therefore probably fosphenytoin) induces the metabolism of lamotrigine, and the recommended starting dose and long-term maintenance dose of lamotrigine in patients already taking phenytoin is twice that of patients receiving lamotrigine monotherapy. However, note that if they are also taking valproate in addition to phenytoin, the lamotrigine dose should be reduced.