# Situation: A 30-year-old man with schizophrenia has had persistent hallucinations despite antipsychotic treatment taken as prescribed. His psychiatrist starts clozapine. His baseline absolute neutrophil count (ANC) was 1.2 × 10⁹/L, and hematology has confirmed benign ethnic neutropenia. He smokes about 20 cigarettes a day. He tells the nurse he plans to stop smoking next week. Why should the nurse inform the prescriber?

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> subject: Nursing Practice V — Care of Clients with Maladaptive Patterns of Behavior; Care of Clients with Life-Threatening Conditions, Acute Multi-Organ Problems, High Acuity and Emergency Situations

## 문제

Situation: A 30-year-old man with schizophrenia has had persistent hallucinations despite antipsychotic treatment taken as prescribed. His psychiatrist starts clozapine. His baseline absolute neutrophil count (ANC) was 1.2 × 10⁹/L, and hematology has confirmed benign ethnic neutropenia. He smokes about 20 cigarettes a day.

He tells the nurse he plans to stop smoking next week. Why should the nurse inform the prescriber?

## 보기

1. Nicotine withdrawal will add to clozapine's risk of neutropenia
2. Nicotine patches interact with clozapine in the liver
3. Smoke speeds clozapine breakdown, so quitting raises his level **✔ 정답**
4. Craving for cigarettes will make his hallucinations worse

**정답: 3**

## 해설

Chemicals in tobacco smoke induce the liver enzyme CYP1A2, which metabolizes clozapine. When a smoker stops, enzyme activity falls and clozapine levels can rise sharply, increasing sedation, hypotension, and seizure risk. The prescriber may reduce the dose and monitor levels.

## 심화 해설

Why Smoking Cessation Requires Prescriber Notification

The key issue here is not the nicotine itself, but the polycyclic aromatic hydrocarbons (PAHs) in tobacco smoke. These chemicals act as potent inducers of the hepatic enzyme CYP1A2, which is the primary metabolic pathway responsible for breaking down clozapine [1][2][4].

When a patient smokes regularly, CYP1A2 activity is upregulated, meaning clozapine is cleared from the body more rapidly. This is why smokers typically require higher doses of clozapine to achieve the same therapeutic plasma concentration as non-smokers [2][4]. In this patient, the prescriber has likely titrated the clozapine dose while he was actively smoking 20 cigarettes per day, so his current dose was calibrated against an induced, faster metabolic state.

Once he stops smoking, the enzyme-inducing stimulus disappears. Over the following days to weeks, hepatic CYP1A2 activity gradually declines back toward a non-smoker baseline [2][4]. With reduced enzyme capacity, the same clozapine dose is metabolized more slowly, leading to a sharp rise in plasma clozapine concentration. This can occur even without any change in adherence or dose.

The clinical consequence is an increased risk of clozapine toxicity. Elevated clozapine levels are associated with dose-dependent adverse effects including excessive sedation, orthostatic hypotension, tachycardia, and—most critically—an increased risk of seizures [1][3]. A published case report describes clozapine intoxication with aspiration pneumonia directly triggered by smoking cessation, underscoring how rapidly and severely levels can climb [3].

Watch out! The patient’s baseline ANC of 1.2 × 10⁹/L with confirmed benign ethnic neutropenia is a separate consideration. Smoking cessation does not directly worsen neutropenia, but if clozapine levels rise excessively, the risk of other serious adverse effects increases. The prescriber must be informed so that a proactive dose reduction and/or therapeutic drug monitoring can be planned before the patient quits.

Key point! The correct response is not that nicotine patches interact with clozapine in the liver, nor that withdrawal adds to neutropenia risk. The mechanism is enzyme induction by smoke constituents, not nicotine. Nicotine replacement therapy does not induce CYP1A2, so it would not cause the same interaction [2]. The prescriber may reduce the clozapine dose and monitor plasma levels during the transition to a non-smoking state.

| Factor | During Smoking | After Smoking Cessation |
| --- | --- | --- |
| CYP1A2 activity | Induced (increased) | Gradually declines to baseline |
| Clozapine clearance | Faster | Slower |
| Clozapine plasma level | Lower at a given dose | Rises sharply at the same dose |
| Risk of adverse effects | Lower relative to dose | Increased sedation, hypotension, seizure risk |
| Nursing implication | Assess smoking status at every visit | Notify prescriber before planned cessation; anticipate dose adjustment and level monitoring |

The nurse should recognize that any change in smoking status—whether starting, increasing, or quitting—is a clinically significant event for a patient on clozapine. The prescriber needs this information to adjust the dose preemptively and monitor clozapine plasma concentrations, rather than waiting for toxicity to develop [1][2][3][4].References (research sources)

- [1]Effects of Repeated Smoking and Quitting Cigarettes on Plasma Concentrations of Clozapine and Its N-Desmethyl and N-Oxide Metabolites in a Japanese Patient With Schizophrenia.Research articleIkawa K, Morikawa N, Sakata M, Horikawa N. (2026) · DOI: 10.1002/npr2.70121

- [2][Smoking cessation and drug interactions].Research articleMadsen HKL, Gulløv M, Farver-Vestergaard I, Hjort P, Nielsen LP, Løkke A (2022)

- [3][Side Effects of Smoking Cessation].Research articleBraun R, Huwiler B (2018) · DOI: 10.1024/1661-8157/a002991

- [4][Tobacco smoking and drug interactions].Research articleMolden E, Spigset O (2009) · DOI: 10.4045/tidsskr.08.0122

## 임상 시나리오

Clozapine and Smoking CessationWhy Quitting Raises Drug Levels
Tobacco smoke contains polycyclic aromatic hydrocarbons that induce CYP1A2, the enzyme that breaks down clozapine. Smokers therefore need higher doses to reach therapeutic levels.

When a patient stops smoking, CYP1A2 activity falls over days to weeks. The same clozapine dose is then cleared more slowly, causing plasma levels to rise sharply.

Elevated clozapine levels increase the risk of dose-dependent toxicity: sedation, orthostatic hypotension, tachycardia, and seizures.

CautionNotify the prescriber before any planned smoking cessation. The dose may need reduction and clozapine levels should be monitored during the transition.

## 핵심 개념

- **CYP1A2** — Hepatic enzyme responsible for clozapine metabolism; induced by polycyclic aromatic hydrocarbons in tobacco smoke.
- **Polycyclic aromatic hydrocarbons (PAHs)** — Chemicals in tobacco smoke that induce CYP1A2, accelerating clozapine clearance in smokers.
- **Clozapine toxicity** — Dose-dependent adverse effects including sedation, hypotension, tachycardia, and seizures when plasma levels rise.
- **Benign ethnic neutropenia** — A normal variant of lower ANC not associated with increased infection risk, distinct from clozapine-induced agranulocytosis.
- **Therapeutic drug monitoring** — Measurement of plasma clozapine levels to guide dosing, especially during changes in smoking status.

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