- Patients taking Itraconazole or Phenytoin will be excluded. Patients must be off of these medications for at least 3 days prior to entering this trial. If the patient is taking phenytoin for seizures at the time of study enrollment, it must be stopped at least 3 days prior to starting therapy and Clonazepam will be substituted during the Busulfex ® infusions and for 24 hours following the infusion.