# Situation: A 52-year-old man with epilepsy is admitted to the medical ward for evaluation of breakthrough seizures. He takes phenytoin 100 mg by mouth three times daily. He has been eating poorly for a month. His total phenytoin level is 12 mcg/mL (therapeutic range 10–20 mcg/mL), and his serum albumin is 2.2 g/dL (normal 3.5–5.0 g/dL). He has new horizontal nystagmus, an unsteady gait, and slurred speech. Which conclusion is BEST supported?

> source: MyMerci (mymerci.kr)  
> url: https://mymerci.kr/pages/nclex_q.php?qn_id=630523  
> language: ko  
> subject: Nursing Practice IV — Care of Clients with Problems in Nutrition and Gastrointestinal, Metabolism and Endocrine, Perception and Coordination

## 문제

Situation: A 52-year-old man with epilepsy is admitted to the medical ward for evaluation of breakthrough seizures. He takes phenytoin 100 mg by mouth three times daily. He has been eating poorly for a month.

His total phenytoin level is 12 mcg/mL (therapeutic range 10–20 mcg/mL), and his serum albumin is 2.2 g/dL (normal 3.5–5.0 g/dL). He has new horizontal nystagmus, an unsteady gait, and slurred speech. Which conclusion is BEST supported?

## 보기

1. The level is therapeutic, so another cause must be found
2. Low albumin raises free phenytoin, so toxicity is likely **✔ 정답**
3. The level is barely in range, so the dose should be raised
4. The findings show that he has been missing his doses

**정답: 2**

## 해설

Phenytoin is highly bound to albumin, and only the free fraction is active. With low albumin, more of the drug is free, so a total level in the normal range can hide a toxic free level; nystagmus, ataxia, and slurred speech are classic signs of phenytoin toxicity. The nurse reports before the next dose, and a free level or albumin-corrected value is obtained.

## 심화 해설

Why a normal total level can hide toxicity
Phenytoin is highly bound to serum albumin, and only the small free (unbound) fraction crosses into the brain and produces both the therapeutic effect and the toxic effect. The usual laboratory test measures the total level, which counts bound and free drug together. The therapeutic range of 10–20 mcg/mL assumes a normal albumin. In this client, albumin is only 2.2 g/dL after a month of poor intake. With fewer albumin binding sites, a much larger share of the drug circulates free, so a total level of 12 mcg/mL can correspond to a free level that is already in the toxic range.

The clinical picture confirms it
The level alone would look reassuring, but the client's findings point the other way. Horizontal nystagmus, an unsteady (ataxic) gait, and slurred speech (dysarthria) are the classic cerebellar signs of phenytoin toxicity. They tend to appear as the free concentration rises: nystagmus first, then ataxia and slurred speech, and later lethargy and confusion. When the numbers and the client disagree, the nurse trusts the clinical signs and asks why the number might be misleading. Low albumin is the explanation here, and it is also common in malnutrition, liver disease, kidney disease, older adults, and critical illness.

| Finding | Value | Meaning |
| --- | --- | --- |
| Total phenytoin | 12 mcg/mL | Looks therapeutic |
| Serum albumin | 2.2 g/dL (normal 3.5–5.0) | Fewer binding sites; free drug rises |
| Nystagmus, ataxia, slurred speech | New | Classic signs of phenytoin toxicity |

Why the other conclusions are wrong
Concluding that the level is therapeutic and that another cause must be found ignores the albumin result and delays recognition of toxicity. Raising the dose because the level is "barely in range" would increase the free drug further and worsen the toxicity he already shows. Missed doses would lower the drug level and could explain his breakthrough seizures, but they do not produce nystagmus and ataxia; those signs come from too much drug, not too little.

Nursing actions
The nurse reports the findings before the next dose so the prescriber can review it. A free phenytoin level or an albumin-corrected value is obtained, and the dose is adjusted. Meanwhile the nurse puts fall precautions in place because of his ataxia, assists with walking, and continues seizure precautions. Nutrition support is also part of the plan, since poor intake caused the low albumin. Other teaching points for phenytoin include good oral hygiene for gingival hyperplasia, consistent timing of doses, and avoiding abrupt discontinuation.

Exam takeaway
Watch out A drug level "within range" does not rule out toxicity for a highly protein-bound drug when albumin is low. Interpret phenytoin levels together with albumin and the client's signs.

## 임상 시나리오

Phenytoin and Low AlbuminReading a total level correctly
Phenytoin is highly bound to albumin; only the free fraction is active. The standard test reports the total level, and its range of 10–20 mcg/mL assumes normal albumin.

With albumin of 2.2 g/dL, more of the drug is free, so a total level of 12 mcg/mL can hide a toxic free level. Nystagmus, ataxia, and slurred speech confirm toxicity.

Report before the next dose, request a free level or corrected value, start fall precautions, and support nutrition.

CautionDo not raise the dose because the total level looks low-normal. In low albumin states, more drug can push the free level further into toxicity.

## 핵심 개념

- **Free phenytoin** — The unbound, active fraction of phenytoin in the blood that produces both therapeutic and toxic effects.
- **Hypoalbuminemia** — A serum albumin below normal, which reduces protein binding sites for highly bound drugs such as phenytoin.
- **Nystagmus** — Involuntary, rhythmic eye movements; horizontal nystagmus is often the first sign of phenytoin toxicity.
- **Ataxia** — Loss of coordination of voluntary movement, seen as an unsteady, wide-based gait.

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