The patient’s phenytoin level is low. Which statement correctly interprets this finding?

• A. Increased risk for seizures due to subtherapeutic levels.
• B. No risk; level is not related to seizure control.
• C. Immediate withdrawal of phenytoin.
• D. Seizure risk is decreased.

Answer: (A)

Low trough levels of phenytoin mean there isn’t enough drug in the blood to reliably prevent seizures. Phenytoin has a narrow therapeutic range, so when the level falls below that range, the medication may not adequately suppress neuronal firing, leading to breakthrough seizures. That’s why the correct interpretation is that there’s an increased risk for seizures due to subtherapeutic levels. Levels outside the therapeutic window do relate to seizure control, so saying there’s no risk isn’t accurate. Immediate withdrawal isn’t indicated and would remove protection against seizures, and saying seizure risk decreases with low levels is the opposite of what actually happens.