Clozapine, an
antipsychotic agent of the dibenzodiazepine class, is characterised by relatively weak central dopaminergic activity and displays atypical pharmacological and clinical properties in relation to the classic
antipsychotics. Clinical studies have shown
clozapine to be effective in suppressing both the positive and negative symptoms of
schizophrenia and to be associated with an extremely low incidence of extrapyramidal side effects.
Clozapine has been shown to be of comparable, or on some criteria superior, therapeutic efficacy to
perphenazine,
levomepromazine,
haloperidol and
chlorpromazine in several short term comparative studies in patients with
schizophrenia of predominantly acute symptomatology. Moreover,
clozapine is effective in a substantial proportion (30 to 50%) of schizophrenic patients who are refractory to or intolerant of classic
antipsychotic therapy. Despite its promising therapeutic potential, the relatively high incidence of
clozapine-induced
agranulocytosis (1 to 2% of patients) is a major factor restricting the
drug's wider use in psychiatric practice. In accordance with current guidelines,
clozapine therapy, performed in conjunction with close haematological monitoring, is indicated for the management of severe and chronic
schizophrenia refractory to classic
antipsychotic therapy, and in those unable to tolerate such
therapy. In such appropriately selected patients,
clozapine represents an important alternative to the classic
antipsychotics.