Phenytoin serum levels were compared in a crossover study of a new 300 mg capsule form and three 100 mg capsules administered once daily. The new 300 mg capsule was equivalent to three 100 mg capsules in efficacy of seizure control and maintenance of phenytoin serum levels. This standard 300 mg dose produced a grand mean drug serum level of 7.63 mcg/ml and was below 10 mcg/ml in 15 to 20 patients. The authors recommend monitoring of phenytoin serum levels and clinical response, to detect needed dosage adjustments for optimum therapeutic benefit from phenytoin and to avoid toxic side effects.
