Clozapine

Jens Richter is editor-in-chief at Since July 2020, the doctor and journalist has also been responsible as COO for business operations and the strategic development of

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Clozapine is a so-called antipsychotic (neuroleptic). It is used in schizophrenia when other drugs do not work or are not tolerated, and in psychoses in the course of Parkinson's disease when standard therapy fails. Before starting treatment, it must be ensured that the patient's blood count is correct. Here you can read everything you need to know about the use, effects and side effects of clozapine.

This is how clozapine works

The active ingredient clozapine is a so-called "atypical neuroleptic". It blocks docking points (receptors) for messenger substances (neurotransmitters) such as dopamine in the central nervous system. An excess of neurotransmitters changes thinking and self-perception and can trigger delusions. Clozapine can therefore normalize brain function by blocking the dopamine receptors.

Clozapine uptake, breakdown and excretion

After ingestion, the active ingredient is almost completely absorbed into the blood through the gastrointestinal tract. It is metabolized almost exclusively in the liver. Clozapine or its metabolic products are partly excreted with the urine and partly with the stool. About 8 to 16 hours after ingestion, half of the active ingredient has already left the body (half-life).

When is clozapine used?

Clozapine is approved for the treatment of:

Schizophrenia, when classic neuroleptics do not work or are not tolerated

This is how clozapine is used

Clozapine is usually given as a tablet, sometimes as an injection (syringe). The dosage is determined individually by the doctor. Therapy is usually gradual: initially a low dose is given, which is then slowly increased to the target dose.Gradually reducing the dose is also recommended to stop therapy.

The prerequisite for treatment is that the patient has normal white blood cell counts before treatment begins: the number of white blood cells and the differential blood count must be normal.

What are the side effects of clozapine?

Blood counts are necessary during treatment and for up to four weeks after the end of therapy because clozapine can cause a deficiency in white blood cells (leukopenia) and a deficiency in granulocytes (agranulocytosis).

Other possible Clozapine side effects are, for example, rest (sedation) up to delirious states, increased salivation at night, weight gain, temporary temperature increase, acute sitting restlessness (akathisia), involuntary muscle twitching (myoclonus), seizures and EEG changes (changes in brain waves ).

Rare side effects are circulatory collapse, acute inflammation of the pancreas, hypoglycaemia (hypergylcaemia) with dangerous metabolic imbalances (ketoacidosis), sudden, severe myocarditis (myocarditis) and sudden, severe liver necrosis (death of liver tissue).

What should be considered when taking clozapine?

Clozapine must not be used in the following cases:

Deficiency of granulocytes: fewer than 3,000 per microliter of blood (granulocytopenia) or even fewer than 500 granulocytes (agranulocytosis) - exception: granulocytopenia / agranulocytosis due to previous chemotherapy
uncontrolled epilepsy
Circulatory collapse and / or CNS depression (drowsiness to deep coma)
acute liver disease with nausea, poor appetite or jaundice

Clozapine must not be used together with drugs that also significantly impair bone marrow function. The combination with so-called depot neuroleptics should also be avoided. The same applies to the combination with the anticonvulsants carbamazepine and phenytoin (anti-epilepsy agents). Other interactions are also possible, which the attending physician must take into account when prescribing.

pregnancy and breast feeding period

If possible, better tested neuroleptics should be used during pregnancy. If a woman becomes pregnant during clozapine therapy and she is well adjusted, it does not necessarily have to be switched to another medication.

Breastfeeding during therapy is conditionally acceptable if the mother is only treated with clozapine alone (monotherapy) and the child is carefully observed by the doctor.