Phenytoin reduces
itraconazole levels (by about 90%).
Ketoconazole may interact similarly with
phenytoin, and fosphenytoin, a prodrug of
phenytoin, may interact similarly with these
azoles.
Concurrent use of
phenytoin and
itraconazole (and probably ketoconazole) should be avoided unless the benefits are expected to outweigh the risks. It seems highly likely that these
azoles will be ineffective.