I am currently being weaned off of Dilantin and on to Keppra XR. I have been taking mg to mg of Dilantin daily for over 20 years and my seizures have always been well controlled and I have had limited side effects. My neurologist recently suggested I switch to a newer drug as she said long term use of Dilantin can. DOSAGE AND ADMINISTRATION The dose, concentration in dosing solutions, and infusion rate of IV fosphenytoin sodium injection is expressed as phenytoin sodium equivalents (PE) to avoid the need to perform molecular weight-based adjustments when converting between fosphenytoin and phenytoin. In convert keppra to dilantin, Coumadin is often disenfranchised as long-term therapy for children with lupus who test positive for.