clozapine

Clozapine is an atypical antipsychotic used primarily for treatment-resistant schizophrenia and for reducing the risk of suicidal behavior in schizophrenia or schizoaffective disorder. It is often reserved for patients who have not adequately responded to other antipsychotics due to a risk profile that requires careful monitoring and management.

The exact mechanism of action is not fully understood. Clozapine acts on multiple neurotransmitter systems, including dopamine and serotonin receptors, and has relatively low occupancy at dopamine D2 receptors compared with many other antipsychotics. It has high affinity for 5-HT2A receptors and also interacts with D4, muscarinic, and adrenergic receptors. This broad receptor activity is thought to contribute to its efficacy on both positive and negative symptoms and its lower propensity to cause extrapyramidal symptoms, though it can cause a distinct set of adverse effects.

Clozapine is taken orally and undergoes extensive hepatic metabolism, mainly via the cytochrome P450 system (notably CYP1A2, with contributions from CYP3A4 and others). Smoking and other substances that induce or inhibit these enzymes can alter clozapine levels. Because of its potential toxicity, its use is typically accompanied by specialized monitoring and, in many countries, a formal blood-testing program.

The most important safety concerns are agranulocytosis and neutropenia, myocarditis and cardiomyopathy, seizures at high doses, and metabolic or anticholinergic side effects such as weight gain, sedation, tachycardia, hypersalivation, and constipation. Due to agranulocytosis risk, patients must have regular white blood cell and absolute neutrophil count (ANC) monitoring, with strict thresholds that determine continuation, interruption, or discontinuation of treatment in collaboration with a monitoring program.

Clozapine remains a valuable option for certain individuals with schizophrenia, balancing its potential to improve symptoms and reduce suicidality against substantial safety and monitoring requirements.