Remarks

1 mL will only allow a single test with no repeat
Samples from patients receiving fosphenytoin should be drawn at least 2 hours following IV administration or 4 hours following IM administration per the recommendations of the manufacturer
The change in the phenytoin concentrations is dependent on the amount of time that has elapsed since the administration of fosphenytoin

This is the preferred test for therapeutic drug management in patients with renal failure or conditions that may alter albumin concentrations