The normal target level for Dilantin or phenytoin, the generic name for this medication, is 10 to 20 microgram per milliliter, reports the U.S. National Library of Medicine. Doctors monitor the level of this drug in patients and adjust the medication to meet therapeutic goals.
Dilantin is commonly used to treat seizure disorders and cardiac arrhythmias, which include heart rhythm problems, such as irregular heartbeats. A blood sample is required to determine a current Dilantin level. This important medication is included on the World Health Organization's List of Essential Medicines, which are critical to a basic health system, notes Wikipedia.