A client who has been taking phenytoin has a repeat phenytoin level of 4 mcg/mL. What should the nurse do next?

• A. Ask the client if they are taking the medication as prescribed.
• B. Increase the dose as ordered.
• C. Discontinue the medication.
• D. Schedule an MRI.

Answer: (A)

Phenytoin monitoring hinges on keeping the drug within a specific range to prevent seizures while avoiding toxicity. For most patients, the therapeutic trough level is about 10–20 mcg/mL. A repeat level of 4 mcg/mL is below this range, signaling inadequate drug exposure and a higher risk of breakthrough seizures.

The first step is to confirm that the patient is taking the medication as prescribed, including checking for missed doses and whether the timing relative to the last dose is correct. This helps determine if nonadherence or timing issues are causing the subtherapeutic level. If adherence is confirmed, then a clinician would review other possibilities (such as absorption problems or drug interactions) and consider a dose adjustment, but changing the dose or discontinuing the medication would require orders from a clinician. Scheduling an MRI isn’t related to the drug level.