Question

Scenario #1:

SS, a 26-year-old woman, takes phenytoin 100 mg t.i.d. to control grand mal seizures. SS and her husband are contemplating starting a family. SS complains of frequent “upset stomach” and “bleeding gums” when brushing her teeth and is questioning if other anticonvulsants are more appropriate than phenytoin.

What are the indications of an abnormal phenytoin serum level?

Answer 1

The indications of an abnormal phenytoin serum level are ascertained by obtaining a serum phenytoin level.

The therapeutic range is 10-20 mcg/mL. Total phenytoin levels (mcg/mL) and the corresponding indications i.e. the signs and symptoms are as follows:

• Lower than 10 - Rare
• Between 10 and 20 - Occasional mild nystagmus
• Between 20 and 30 - Nystagmus
• Between 30 and 40 - Ataxia, slurred speech, nausea, and vomiting
• Between 40 and 50 - Lethargy and confusion
• Higher than 50 - Coma and seizures