A client on phenytoin has a very low albumin level. The phenytoin level is expected to be which?

• A. High
• B. Low
• C. Normal
• D. Unchanged

Answer: (A)

Phenytoin binds strongly to albumin, so how much albumin is present directly changes how much drug is bound versus free. When albumin is very low, less phenytoin is bound and more remains unbound in the bloodstream. The unbound portion is the pharmacologically active part, so the overall exposure to phenytoin (the corrected or true exposure) is higher than what the total measured level would suggest. In other words, with low albumin, the free phenytoin is increased, and the corrected total phenytoin level is high, even if the standard total level appears normal or low. This is why clinicians pay attention to albumin when interpreting phenytoin levels and may calculate a corrected value to reflect the true exposure.