Phenytoin Levels on the NCLEX
Therapeutic range, free vs total, albumin adjustment.
Phenytoin has a narrow therapeutic index. Levels guide dosing.
Therapeutic
10-20 mcg/mL total. Toxic >20.
Toxicity signs
Nystagmus (early), ataxia, slurred speech, confusion, coma at very high levels.
Albumin adjustment
Phenytoin protein-bound. Low albumin → falsely low total level. Check free phenytoin if albumin low.
Chronic side effects
Gingival hyperplasia, hirsutism, B12/folate deficiency.
Frequently asked
Saturable kinetics?
Phenytoin is zero-order. Small dose increase can cause large level jump at high range.
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