BSN Tracker

clozapine

Brand: Clozaril, FazaClo, Versacloz

⚠ BBW Beers Criteria TDM Required Prototype Drug
Drug Class: second-generation antipsychotic (SGA)
Drug Family: antipsychotic
Subclass: dibenzodiazepine; atypical antipsychotic
Organ Systems: cns

Mechanism of Action

Unique antipsychotic with weak D2 blockade but potent D4, 5-HT2A, and broad receptor binding. Low D2 occupancy explains near-zero EPS risk. Its precise mechanism of action for treatment-resistant schizophrenia remains incompletely understood but likely involves complex multimodal effects across dopaminergic, serotonergic, and other systems.

D4 dopamine receptor (high affinity)D1 receptorD2 receptor (low affinity)5-HT2A receptormuscarinic receptors (M1-M4)H1 histamine receptoralpha-1 adrenergic receptorGABA-B receptor

Indications

  • treatment-resistant schizophrenia (defined as failure of ≥2 adequate antipsychotic trials)
  • reducing suicidal behavior in patients with schizophrenia or schizoaffective disorder

Contraindications

  • history of clozapine-induced agranulocytosis
  • myeloproliferative disorders
  • paralytic ileus
  • concurrent drugs that markedly suppress bone marrow

Adverse Effects

Common

  • sedation
  • hypersalivation (paradoxical)
  • weight gain (most among SGAs)
  • constipation
  • tachycardia
  • hypotension

Serious

  • agranulocytosis (1-2%; fatal if untreated)
  • myocarditis and cardiomyopathy (especially in first month)
  • seizures (dose-dependent; 3-5% at doses >600 mg)
  • metabolic syndrome
  • ileus and bowel obstruction

Pharmacokinetics (ADME)

Absorption oral bioavailability ~60-70%; food has minimal effect
Distribution protein binding ~97%; Vd ~1.6 L/kg; crosses BBB readily
Metabolism primarily CYP1A2 (major) and CYP3A4; active metabolites include norclozapine
Excretion renal (~50%) and fecal (~30%)
Half-life 8-16 hours
Onset therapeutic response 6-8 weeks; clinical trial minimum 6 months
Peak 2.5 hours
Duration 12-24 hours
Protein Binding 97%
Vd 1.6 L/kg

Drug Interactions

Drug / Agent Mechanism Severity
fluvoxamine potent CYP1A2 inhibition increases clozapine levels 5-10 fold major
carbamazepine CYP3A4 induction reduces clozapine levels AND additive agranulocytosis risk contraindicated
smoking (tobacco) CYP1A2 induction reduces clozapine levels by ~50%; smoking cessation increases levels major
benzodiazepines excessive sedation and respiratory depression, especially at initiation major

Nursing Considerations

  1. Clozapine requires enrollment in the FDA REMS program; absolute neutrophil count (ANC) must be measured at baseline and weekly for 6 months, then biweekly for 6 months, then monthly — clozapine must not be dispensed without documented current ANC.
  2. ANC thresholds: ANC ≥1500/μL to initiate; hold if ANC <1000/μL; permanently discontinue if ANC <500/μL (agranulocytosis); educate patient to report any fever, sore throat, or infection immediately.
  3. Smoking status dramatically affects clozapine levels; if a patient stops smoking while on clozapine, levels can increase by 50-100%, potentially causing toxicity — document and report any smoking status changes.
  4. Hypersalivation is paradoxical (muscarinic agonism via active metabolites) and may be addressed with low-dose anticholinergics or alpha-2 agonists; monitor for aspiration risk in sedated patients.

Clinical Pearls

  • Clozapine is the most effective antipsychotic for treatment-resistant schizophrenia and the only drug shown to reduce suicidality in schizophrenia, yet it is vastly underused due to monitoring burden and fear of agranulocytosis.
  • The clozapine REMS system allows real-time monitoring of ANC across all prescribers and pharmacies; the dispensing pharmacy cannot release clozapine without a confirmed current ANC — this is a safety system of exceptional rigor.

Safety Profile

Pregnancy use-with-caution
Lactation avoid
Renal Adjustment Not required
Hepatic Adjustment Required
TDM Required

Concordance Terms

Cross-referenced clinical concepts — click any term to see all content where it appears.

Reducing Suicidal Behavior In Patients With Schizophrenia Or Schizoaffective Disorder Second-generation Antipsychotic (SGA) Treatment-resistant Schizophrenia (defined As Failure Of ≥2 Adequate Antipsychotic Trials)
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