Clozaril (clozapine) is an antipsychotic approved by the U.S. Food and Drug Administration to treat severely ill patients with schizophrenia who do not respond to other antipsychotics.

Clozaril can also be used to manage psychotic symptoms in patients with Huntington’s disease when other medications fail.

How Clozaril works

From 6-25 percent of Huntington’s disease patients experience psychotic symptoms, which includes delusions and hallucinations.

These symptoms are thought to develop when there are disturbances in chemical messengers or neurotransmitters in the brain known as dopamine and serotonin. Brain damage that occurs in Huntington’s disease affects the delicate balance of these neurotransmitters.

Clozaril is a second-generation antipsychotic. This means that unlike first-generation antipsychotics that only act on dopamine D2 receptors, Clozaril acts on both dopamine D2 receptors and serotonin 5HT2A receptors.

While researchers are still investigating exactly how Clozaril works, its action on these receptors appears to correct the underlying neurotransmitter imbalance, relieving psychotic symptoms.

Clozaril in clinical trials

Clozaril is an established antipsychotic medication in patients who do not respond to other types of antipsychotics. Although there have not been controlled clinical trials specifically in Huntington’s disease patients, the medicine is commonly used off-label for these patients.

While some antipsychotics may be used to treat chorea in Huntington’s, Clozaril typically is not used to manage this symptom. A study of 33 patients with Huntington’s disease who received a daily dose of 150 mg of Clozaril for 31 days did not experience improvements in chorea or voluntary motor movements.

Additional details

Common side effects of Clozaril are drooling due to increased salivation, sedation, drowsiness, fast heart rate, weight gain, dizziness, vertigo, and constipation.

On rare occasions, Clozaril may trigger a person’s bone marrow to produce less or stop producing white blood cells, a phenomenon known as agranulocytosis. Agranulocytosis affects about 1-2 percent of patients who have been taking Clozaril for a year and can be fatal if not detected early.

People who are taking Clozaril should have regular visits to their treating physicians; certain blood tests are necessary to monitor the safety and effectiveness of Clozaril.

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