A patient of schizophrenia on CPZ (chlorpromazine) develops auditory hallucination again. The next drug to be given is -

Auditory hallucinations (positive symptoms) are the first symptoms to respond. If auditory hallucinations do not respond or reappear while the patient is on treatment, resistant schizophrenia should be suspected. "Clozapine (but not newer atypicals) is more effective than classical agents for resistant schizophrenia"