Phenobarbital (given with
carbamazepine or phenytoin) has been shown to decrease
itraconazole levels resulting in treatment failure.
Phenobarbital is predicted to decrease
posaconazole and
voriconazole levels. Note that
primidone is metabolised to
phenobarbital and therefore may interact similarly with these
azoles.
Concurrent use should be avoided unless the benefits are expected to outweigh the risks, although note that the manufacturers contraindicate the use of voricona- zole. If concurrent use is necessary it seems likely that the antifungal dose will need to be increased. It would seem prudent to use other alternatives wherever possible or monitor concurrent use very closely.