After discovering a low phenytoin level, what should the nurse do next?

• A. Clarify adherence and determine reason for nonadherence.
• B. Increase dose immediately.
• C. Discontinue therapy.
• D. Switch to a different anticonvulsant.

Answer: (A)

When a phenytoin level is low, the most important next step is to verify whether the patient is taking the medication as prescribed and to uncover the reason for any nonadherence. Phenytoin has a narrow therapeutic window, so subtherapeutic levels often reflect missed doses, irregular dosing times, or barriers to taking the drug (such as cost, access, forgetfulness, or side effects) rather than an immediate need to change the regimen.

By clarifying adherence and understanding why it’s not being followed, the nurse can target the underlying issue—provide education, plan reminders, simplify dosing, or address access problems—and monitor if the level rises after those barriers are addressed. Only after confirming adherence and identifying any barriers should adjustments to the regimen be considered; jumping to a higher dose without this check risks toxicity if the patient does eventually take the medication consistently or if interactions or absorption issues complicate the picture. Discontinuing therapy or switching anticonvulsants would not address the immediate subtherapeutic level and could leave the patient at risk for seizures.