For the first time in over 20 years my dilantin levels have spiked to 91, why. i was taking 400 mg a day. i recently had major surgery and i am 59. ?

Other med: An additional med related to the condition for which you had surgery may be the culprit. Liver function changes also should be considered.

Dilantin is peculiar: This drug was developed over 80 years ago, and due to it's zero order kinetics, would never be approved by fda today. Simply, the drug-drug interactions can be a trivial nudge which inhibits liver metabolism and shoots levels sky high. The degree of elevation in you is dangerous, and suggests you would do far better getting off this archaic drug and using a modern, less troublesome medicine.