- The therapeutic ranges for phenytoin (dilantin) and phenobarbital in adults are 10 to 20 mcg/mL and 10 to 30 mcg/mL, respectively.
- Phenytoin plasma levels rise more rapidly than phenobarbital levels; therefore, an acute overdose of the two together will likely manifest as phenytoin toxicity before phenobarbital toxicity.
- Phenytoin has a more narrow margin between therapeutic and toxic levels than does phenobarbital.