PHENYTOIN AND SIROLIMUS
The manufacturers predict that phenytoin (and therefore possibly fosphenytoin) may lower the serum levels of sirolimus, probably because rifampicin (rifampin), another CYP3A4 inducer, has been shown to do so. This prediction seems to be confirmed by 2 patients who needed an increase in their sirolimus doses when they were given phenytoin.
The extent of any change in sirolimus levels is uncertain, but it would seem prudent to increase the frequency of monitoring sirolimus levels, both during concurrent use and also if phenytoin is withdrawn.
The extent of any change in sirolimus levels is uncertain, but it would seem prudent to increase the frequency of monitoring sirolimus levels, both during concurrent use and also if phenytoin is withdrawn.