Overview
Clozapine is an atypical antipsychotic medication primarily used for treatment-resistant schizophrenia. It has a unique receptor binding profile with strong affinity for serotonin, dopamine, histamine, and adrenergic receptors. Due to its risk of severe neutropenia, it requires mandatory blood monitoring through the Clozapine REMS program.
Mechanism of Action
Clozapine acts as an atypical antipsychotic with complex receptor binding. It has high affinity for serotonin 5-HT2A receptors (antagonism) and relatively lower affinity for dopamine D2 receptors compared to typical antipsychotics. It also binds to histamine H1, adrenergic α1, muscarinic M1, and various serotonin receptors, contributing to its efficacy and side effect profile with minimal prolactin elevation.
Indications
- Treatment-resistant schizophrenia in patients unresponsive to standard antipsychotics
- Reducing suicidal behavior in patients with schizophrenia or schizoaffective disorder
Common Doses
- 12.5 mg
- 25 mg
- 50 mg
- 100 mg
- 150 mg
- 200 mg
Dosage
Initial dose typically 12.5 mg once or twice daily, gradually titrated upward based on tolerability. Target dose range is 300-450 mg/day divided into multiple doses, with maximum dose of 900 mg/day. Requires gradual titration over several weeks to minimize orthostatic hypotension and sedation.
Contraindications
- History of hypersensitivity to clozapine or any component of the formulation
- History of clozapine-induced agranulocytosis or severe neutropenia
- Uncontrolled epilepsy
- Paralytic ileus
- Severe central nervous system depression or comatose states
Side Effects
- Sedation/drowsiness
- Hypersalivation (sialorrhea)
- Orthostatic hypotension
- Tachycardia
- Constipation
- Weight gain
- Fever
- Dizziness
- Headache
- Nausea/vomiting
- Seizures (at higher doses)
- Agranulocytosis/neutropenia (requires monitoring)
- Myocarditis
- Metabolic syndrome components
Interactions
- Benzodiazepines and other CNS depressants: increased risk of respiratory depression and hypotension
- Strong CYP1A2 inhibitors (fluvoxamine, ciprofloxacin): increased clozapine levels
- CYP1A2 inducers (carbamazepine, phenytoin, tobacco smoking): decreased clozapine levels
- Drugs that prolong QT interval: additive risk of cardiac arrhythmias
- Anticholinergic agents: increased risk of anticholinergic toxicity
- Warfarin: potential altered anticoagulant effect
Counseling Points
- Mandatory blood monitoring required for neutropenia risk - explain Clozapine REMS program
- Report fever, sore throat, or signs of infection immediately
- Rise slowly from sitting/lying position to prevent dizziness
- Avoid alcohol and other CNS depressants
- Report rapid heart rate, chest pain, or shortness of breath
- Maintain regular monitoring of blood glucose and lipids
- Do not stop medication abruptly due to risk of withdrawal and psychosis recurrence
- Use caution when driving or operating machinery due to sedation