An adherent patient is receiving 400 mg/day of phenytoin sod…

An adherent patient is receiving 400 mg/day of phenytoin sodium capsules in divided doses and his total phenytoin concentration at steady state is [C1] mg/L. He becomes NPO and requires IV dosing.    Assuming a KM of 4mg/L, what do you expect the steady state phenytoin concentration to be if he is switched to fosphenytoin IV and the daily dose of phenytoin equivalents is decreased by 25mg? (Fosphenytoin is dosed in units of phenytoin base equivalents, so should be considered phenytoin base.  Phenytoin sodium is 92% phenytoin.)