“Patient frequency … for total carnitine was 20% of all patients (10% for free carnitine), 23% of … receiving valproate (9% for free carnitine), 36% of those receiving phenobarbital (21% for free carnitine), 12% of those receiving phenytoin (8% for … carnitine), and 8% of those receiving carbamazepine (1% for free carnitine).”