Several lines of evidence suggest that Clozapine is more effective than others antipsychotic drugs in treatment-resistant schizophrenia (TRS). It would therefore be extremely valuable if predictors of response to Clozapine could be identified.

The aim of this study was to evaluate the predictive factors of clinical responses to Clozapine in a group of patients with TRS.

We had studied 42 TRS patients (8 males and 34 females) receiving Clozapine. All patients inthis study fulfilled the criteria for refractory schizophrenia according to the UK guidelines for the for the National Institute of Clinical Excellence (NICE).

Psychopathology was evaluated before the initiation of Clozapine therapy and after 4 weeks using the Brief Psychiatric Rating Scale (BPRS), the Scale for the Assessment for Positive Symptoms (SAPS), and the Scale for the Assessment of Negative Symptoms (SANS).

Of the TRS patients on Clozapine, 61.9% achieved a clinical response, defined as at least a 20% decrease in BPRS.

There were no correlation between gender, age, educational level and Clozapine response.

The different subtypes of schizophrenia have shown no differences in therapeutic response.

There was no correlation between response and daily doses of Clozapine (relative to dose per kg of body weight).

A good Clozapine response was more likely when schizophrenia began at a later age (p= 0.007) and when negative symptoms were severe (p= 0.009).

In our study 61.9% of TRS patients on Clozapine had a clinical response. Priority should be given for patients with evident negative symptom.